Rock Solid - A Scientific Review

Rock Solid?
A GeneWatch UK consultancy report

Rock Solid?
A scientific review of geological disposal of
high-level radioactive waste
Written by Helen Wallace for Greenpeace International
September 2010
Contact details
Greenpeace EU Unit
Jan Haverkamp
Email: jan.haverkamp@greenpeace.org
GeneWatch UK
60 Lightwood Road, Buxton, Derbyshire SK17 7BB
Phone: 01298 24300
Email: mail@genewatch.org Website: www.genewatch.org
GeneWatch
Registered in England and Wales Company Number 3556885
UK
GeneWatch UK consultancy report

September 2010 1
2 September 2010
Acknowledgements
The author is grateful to Dr Rachel Western for drawing her attention to Nuclear Waste Advisory
Associates' Issues Register and a number of the other publications cited; and to Dr. Rianne Teule and
the advisory group from Greenpeace International for their helpful comments on a draft of this report.
Cover
The cover photograph by Eric Shmuttenmaer is licensed under a Creative Commons Attribution-
Share Alike 2.0 Generic license. The world's first nuclear reactor was rebuilt at this site in Red Gate
Woods near Chicago in 1943 after initial operation at the University of Chicago.

September 2010 3
Contents
Executive summary .............................................................................................................7

1. Introduction ..............................................................................................................9
2. Nuclear power and radioactive waste ....................................................................11
2.1. Harmful effects of radioactive wastes .................................................................13
3. The concept of deep geological disposal. .............................................................17
3.1. Safety assessment ...........................................................................................18
3.2. National programmes for geological disposal ................................................... 19
3.3. Potential for significant radiological releases? ...................................................21
4. Literature review of post-closure issues ..............................................................23
4.1. Corrosion of canisters, wastes, and repository structures .................................23
4.1.1. Corrosion of copper................................................................................23
4.1.2. Corrosion of copper by water ............................................................... 24
4.1.3. Role of microbes .................................................................................. 24
4.1.4. Steel corrosion and hydrogen gas generation .......................................25
4.1.5. Creep ....................................................................................................25
4.1.6. Summary of corrosion issues.................................................................26
4.2. Bentonite erosion and loss of buffer capacity...................................................26
4.2.1. Effects of heat and mineral changes on bentonite ................................ 26
4.2.2. Effects of saline water ............................................................................28
4.2.3. Effects of other minerals in clay .............................................................28
4.2.4. Chemical disturbance due to corrosion..................................................28
4.2.5. Effects of gas on the clay barrier............................................................29
4.2.6. The role of microbes: gas production and biomineralisation..................30
4.2.7. Summary of bentonite erosion and loss of buffer capacity ....................31
4.3. Solubility, sorption and transport of radionuclides ...........................................31
4.3.1. Geochemistry and buffer chemistry........................................................31
4.3.2. Colloids and complexation .....................................................................32
4.3.3. The role of microbes...............................................................................32
4.3.4. Release of radioactive gas .....................................................................33
4.3.5. Summary of solubility, sorption and transport of radionuclides ..............33
4.4. Bedrock properties and hydrogeology ...............................................................33
4.4.1. Groundwater flow in the bedrock and fractures .....................................33
4.4.2. Excavation damage................................................................................35
4.4.3. Gas flow ................................................................................................36
4.4.4. Summary of bedrock properties and hydrogeology ...............................36

4 September 2010
4.5. Human intrusion and human error ...................................................................36
4.6. Ice ages and glaciation.....................................................................................36
4.7. Earthquakes .....................................................................................................38
4.8. Transport of radionuclides in the biosphere .....................................................38
5. Overarching unresolved issues ...........................................................................40
5.1. Safety assessment: the evidence base, the
methodology and its limitations .......................................................................40
5.1.1. Unknowns, uncertainties and model validation ......................................40
5.1.2. Potential for bias in the assessment process .........................................42
5.2. Site selection, public opinion and radioactive waste inventories......................43
5.3. Costs ................................................................................................................46
6. Conclusion .............................................................................................................48

September 2010 5
Index of Boxes and Figures
List of text boxes

Box 1: Categories of radioactive waste....................................................................11
Box 2: Nuclear reprocessing ................................................................................. 12
Box 3: Radioactivity ...............................................................................................13
Box 4: Health effects of ionising radiation . .............................................................. 14
Box 5: Radionuclides and deep geological disposal ................................................15
Box 6: Existing difficulties with geological repository programmes ..........................20
Box 7: The Swedish concept...................................................................................21
Box 8: The French concept .....................................................................................21
List of figures
Figure 1: Decay in radiotoxicity of spent nuclear fuel ..................................................16

6 September 2010
Executive Summary
Worldwide, thirteen countries are actively pursuing long-term waste management

programmes for high-level radioactive wastes resulting from nuclear electricity generation,
but no country has yet completed an operational geological disposal facility for such wastes.
The European Commission Joint Research Centre’s 2009 conclusion that the technology of
geological disposal has developed well enough to proceed with stepwise implementation is
based largely on a description of ongoing research projects and nuclear agency reports, and
references only three papers published in scientific journals. Further, the Centre’s report
falsely claims that it is mainly due to a lack of public acceptance that repository programmes
in Germany and the UK have (temporarily) foundered, rather than because of safety issues.
Similarly, the statement of the Organisation for Economic Co-operation and Development’s
(OECD’s) Nuclear Energy Agency (NEA) that “geological disposal is technically feasible” and
that a “geological disposal system provides a unique level and duration of protection for high
activity, long-lived radioactive waste” is based on the collective views of its Radioactive
Waste Management Committee, not on an analysis of the existing scientific evidence.
Based on a literature review of papers in scientific journals, the present report provides an
overview of the status of research and scientific evidence regarding the long-term
underground disposal of highly radioactive wastes.
This review identifies a number of phenomena that could compromise the containment
barriers, potentially leading to significant releases of radioactivity:
l Copper or steel canisters and overpacks containing spent nuclear fuel or high-level
radioactive wastes could corrode more quickly than expected.
l The effects of intense heat generated by radioactive decay, and of chemical and
physical disturbance due to corrosion, gas generation and biomineralisation, could
impair the ability of backfill material to trap some radionuclides.
l Build-up of gas pressure in the repository, as a result of the corrosion of metals and/or
the degradation of organic material, could damage the barriers and force fast routes
for radionuclide escape through crystalline rock fractures or clay rock pores.
l Poorly understood chemical effects, such as the formation of colloids, could speed up
the transport of some of the more radiotoxic elements such as plutonium.
l Unidentified fractures and faults, or poor understanding of how water and gas will flow
through fractures and faults, could lead to the release of radionuclides in groundwater
much faster than expected.
l Excavation of the repository will damage adjacent zones of rock and could thereby
create fast routes for radionuclide escape.
l Future generations, seeking underground resources or storage facilities, might
accidentally dig a shaft into the rock around the repository or a well into contaminated
groundwater above it.
l Future glaciations could cause faulting of the rock, rupture of containers and
penetration of surface waters or permafrost to the repository depth, leading to failure
of the barriers and faster dissolution of the waste.
l Earthquakes could damage containers, backfill and the rock.
Although computer models of such phenomena have undoubtedly become more
sophisticated, fundamental difficulties remain in predicting the relevant complex, coupled

September 2010 7
processes (including the effects of heat, mechanical deformation, microbes and coupled gas
and water flow through fractured crystalline rocks or clay) over the long timescales
necessary. In particular, more advanced understanding and modelling of chemical reactions
is essential in order to evaluate the geochemical suitability of repository designs and sites.
The suitability of copper, steel and bentonite as materials for canisters, overpacks and
backfill also needs to be reassessed in the light of developing understanding of corrosion
mechanisms and the effects of heat and radiation.
Unless and until such difficulties can be resolved, a number of scenarios exist in which a
significant release of radioactivity from a deep repository could occur, with serious
implications for the health and safety of future generations. In this light, the existence in a
number of countries of ‘road maps’ for the implementation of deep disposal, and the
rejection of other options, do not automatically mean that deep disposal of highly radioactive
wastes is safe.
At present, the following issues remain unresolved and have implications for policy
development:
l the high likelihood of interpretative bias in the safety assessment process because of
the lack of validation of models, the role of commercial interests and the pressure to
implement existing road maps despite important gaps in knowledge. Lack of (funding
for) independent scrutiny of data and assumptions can strongly influence the safety
case
l lack of a clearly defined inventory of radioactive wastes, as a result of uncertainty
about the quantities of additional waste that will be produced in new reactors,
increasing radioactivity of waste due to the use of higher burn-up fuels, and
ambiguous definitions of what is considered as waste
l the question of whether site selection and characterisation processes can actually
identify a large enough volume of rock with sufficiently favourable characteristics to
contain the expected volume of wastes likely to be generated in a given country
l tension between the economic benefits offered to host communities and long-term
repository safety, leading to a danger that concerns about safety and impacts on
future generations may be sidelined by the prospect of economic incentives, new
infrastructure or jobs. There is additional tension between endorsement of deep
disposal as a potentially ‘least bad’ option for existing wastes, and nuclear industry
claims that deep repositories provide a safe solution to waste disposal and so help to
justify the construction of new reactors
l potential for significant radiological releases through a variety of mechanisms,
involving the release of radioactive gas and/or water due to the failure of the near-field
or far-field barriers, or both
l significant challenges in demonstrating the validity and predictive value of complex
computer models over long timescales
l risk of significant escalation in repository costs.

8 September 2010
1. Introduction
This report examines the current state of scientific evidence regarding the geological disposal of
spent nuclear fuel and other high-level and long-lived radioactive wastes.
The European Atomic Energy Community (Euratom), which was founded in 1957 to promote the use
of nuclear power in Europe, has been financing research in the area of geological disposal of high-
level radioactive waste for more than three decades and has provided considerable support to
1
national research and development programmes.
Worldwide, thirteen countries are actively pursuing long-term waste management programmes for
high-level radioactive wastes resulting from nuclear electricity generation, but no country has yet
2
completed an operational geological disposal facility for such wastes.
The 2009 Euratom-funded Vision Document of the European Implementing Geological Disposal of
Radioactive Waste Technology Platform (IGD-TP) states that “a growing consensus exists” that deep
disposal is the most appropriate solution to disposing of spent nuclear fuel, high-level waste and
other long-lived radioactive wastes, and that it is time to proceed to licensing the construction and
operation of deep geological repositories for radioactive waste disposal.3 This conclusion is
supported by the 2009 report of the European Commission’s (EC’s) Joint Research Centre (JRC),
which states that “our scientific understanding of the processes relevant for geological disposal has
developed well enough to proceed with step-wise implementation”.4
The IGD-TP Vision Document has been prepared by an Interim Executive Group with members from
the nuclear waste management organisations SKB (Sweden), Posiva (Finland) and Andra (France)
and the German Federal Ministry of Economics and Technology (BMWi). It adopts the vision that by
2025 the first geological disposal facilities for spent nuclear fuel, high-level waste and other long-
lived radioactive waste will be operating safely in Europe. The Director of Energy (Euratom) for the
European Commission’s Directorate-General for Research states in the Foreword:
These will not only be the first such facilities in Europe but also the first in the world. I am
convinced that through this initiative, safe and responsible practices for the long-term
management of hazardous radioactive waste can be disseminated to other Member States
and even 3rd countries, thereby ensuring the greatest possible protection of all citizens and
5
the environment both now and in the future.
The IGD-TP states that inherent in “all the successful outcomes to date in European nuclear waste
management programmes” are judgements that safe geological disposal of spent nuclear fuel, high-
level waste, and other long-lived radioactive waste is achievable: “In this context, the future RD&D
[Research, Development and Demonstration] issues to be pursued, including their associated
uncertainties, are not judged to bring the feasibility of disposal into question.” This statement reflects
the view expressed by the Radioactive Waste Management Committee (RWMC) of the OECD’s
Nuclear Energy Agency (NEA)6 that “geological disposal is technically feasible” and that a “geological
disposal system provides a unique level and duration of protection for high activity, long-lived
radioactive waste”.
However, the OECD/NEA position is merely a collective statement, based on the views of the
RWMC, not an analysis of the existing scientific evidence. Similarly, the IGD-TP report relies on a
road map towards radioactive waste management developed by the European Nuclear Energy
Forum7, and includes no references to papers in scientific journals. The EC’s JRC report is largely a
description of ongoing research projects; it cites only three papers published in academic journals
(one of which dates from 1999) plus lists of background reports, largely published by the NEA and
International Atomic Energy Agency (IAEA), and a few conference papers. The report makes no
obvious links between these summaries of research activity and its conclusion that Europe is ready
to proceed to implementation of deep geological disposal.8 In a rare example of a referenced claim,
the JRC’s statement that corrosion of steel (and the generation of hydrogen gas by this process) will
not compromise the safety of a repository is based solely on an unpublished note of a panel
discussion held in Brussels in 2007. Further, the report falsely claims that repository programmes in

September 2010 9
Germany and the UK have “(temporarily) foundered mainly for reasons of public acceptance”, rather
than because of safety issues.
In contrast, the present report is based on a literature review of research on deep disposal published
in peer-reviewed scientific journals. It provides an overview of the status of research and scientific
evidence regarding the long-term underground storage of highly radioactive wastes, and asks
whether this evidence supports the view that such wastes can be disposed of safely underground. It
finds that significant scientific uncertainties remain and it accordingly questions whether strong
conclusions in favour of deep disposal can be drawn until all the relevant issues have been
addressed.

10 September 2010
2. Nuclear power and radioactive waste
9
Nuclear reactors are used to generate electricity in 31 countries in the world. Currently, there are
438 operational nuclear power plants in the world, with a total net installed capacity of 372.038
GW(e).10
The IAEA lists 61 nuclear power reactors as currently under construction, mainly in China, Russia,
11
South Korea and India. In Europe, new reactors are being built at Olkiluoto in Finland, Flamanville
in France and Mochovce in the Slovak Republic. Globally, China is expected to be the fourth largest
12
generator of nuclear power by 2025, behind the USA, France and Japan.
Nuclear electricity generation creates large quantities of radioactive wastes, not only in nuclear
power plants themselves, but at all stages of the nuclear chain, from uranium mining to
decommissioning of nuclear facilities. The most highly radioactive wastes are those which are
produced in the core of the reactor. The focus of this report is on spent nuclear fuel: this is nuclear
fuel that has been involved in the nuclear chain reaction at the heart of the reactor (see Box 1).
Some countries intend to dispose of spent nuclear fuel directly, but in other countries it is first
reprocessed (Box 2). Reprocessing changes the characteristics of the wastes that will ultimately be
sent to a repository.
The amount of radioactive waste produced in a reactor depends on the reactor type. On the basis of
data from 1992, the IAEA estimates that one year’s operation of a Light Water Reactor (LWR)
producing 1GW of power typically results in spent fuel assemblies containing a total of 30 to 50
metric tonnes of heavy metal , with an initial activity of around 5 to 8.3 million TBq of radioactivity.13
According to the IAEA, current reprocessing procedures would separate about 15m3 of vitrified high-
level radioactive waste from this quantity of spent fuel. These figures are indicative only and have
changed significantly with time. More modern reactors using higher burn-up fuel will produce smaller
quantities of spent fuel but with higher levels of radioactivity per fuel rod. These changes can have
14
significant implications for the safety case for a repository.
Box 1: Categories of radioactive waste

Naturally Occurring Radioactive Material (NORM) includes radioactive wastes created by
mining and milling of naturally occurring uranium ores in order to produce fuel for nuclear
reactors.
Low-Level Waste (LLW) makes up the bulk of the volume of waste produced in the nuclear fuel
chain. It consists of materials such as paper, rags, tools, clothing and filters, which may contain
small amounts of mostly short-lived radioactivity.
Intermediate-Level Waste (ILW) contains higher levels of radioactivity and normally requires
shielding. It includes resins, chemical sludges, metal fuel cladding, and contaminated materials
from the decommissioning of reactors or from nuclear reprocessing. Short-lived ILW is typically
disposed of in shallow land burial, but long-lived ILW is destined for geological disposal.
High-Level Waste (HLW) and Spent Nuclear Fuel both contain fission products (radioactive
elements created when atoms are split in the nuclear chain reaction) and transuranic elements
(see Box 5) generated in the reactor core. These are highly radioactive and generate heat due
to radioactive decay. In countries where spent nuclear fuel is reprocessed, liquid high-level
waste is separated from other radioactive waste streams (see Box 2) and is vitrified (turned into
glass blocks) before disposal. Depending on the waste disposal concept the heat-generating
spent fuel and high-level waste require a cooling period of up to several decades prior to
ultimate disposal.

September 2010 11
Box 2: Nuclear reprocessing
Nuclear reprocessing involves treating spent nuclear fuel by means of a chemical process
15
(usually by dissolving it in nitric acid ) after it has been removed from the reactor and stored for
several years. The spent fuel is separated into plutonium, uranium, and high-level and
intermediate-level wastes, and radioactive waste streams are also discharged as liquids into the
sea or other water courses and as gases to air.
Liquid high-level wastes are stored in tanks, which require constant cooling, and are later
vitrified (turned into glass blocks). The volume of high-level waste contained in these glass
16
blocks is smaller than the volume of the original spent nuclear fuel. However, reprocessing
increases the total volume of radioactive material, and creates a large volume of long-lived
intermediate-level wastes, which are usually also considered to require deep underground
17
disposal.
Four countries (France, India, Russia and the UK) currently have reprocessing plants which take
spent nuclear fuel from non-military reactors on a commercial scale, while Japan and China
18
have pilot plants and aim to reprocess commercially in the future. Reprocessing facilities were
originally developed to extract plutonium from spent nuclear fuel in order to make nuclear
weapons. The separated plutonium from commercial reprocessing is now mainly added to
existing stockpiles, although small quantities are used in the production of mixed-oxide (MOX)
nuclear fuel. Separated uranium was originally intended to be reused as nuclear fuel, but at
present this rarely happens, probably as a result of its poor quality compared with fresh uranium
(due to contamination with unwanted uranium isotopes).
France, the UK, Russia and China are nuclear weapons states with a significant legacy of
wastes from nuclear reprocessing for weapons production, as well as from their ongoing civil
nuclear programmes. Reprocessing in these countries continues to generate large amounts of
19
liquid high-level wastes. Japan has sent large quantities of spent fuel to the UK and France but
is now planning to reprocess its own fuel. The USA reprocessed spent nuclear fuel in the past,
although not on a commercial scale. It ceased the practice in 1997 due to concerns about the
nuclear proliferation risks associated with separated plutonium, along with a combination of
severe technical, economic and safety problems.20
In Europe, the Sellafield site in England and La Hague in France are the main reprocessing
plants. Significant radioactive discharges to sea and air have been made from both sites over
the past 60 years.21 The Strategy on Radioactive Substances adopted by the Oslo and Paris
Convention (OSPAR) in 1998, which covers discharges to sea in the North-East Atlantic area,
requires that by the year 2020 the discharges, emissions and losses of radioactive substances
be reduced to levels where the additional concentrations in the marine environment above
22
historic levels resulting from such discharges, emissions and losses are close to zero. With the
exception of UK and France, OSPAR member states interpreted the Strategy to mean that
reprocessing should cease and be replaced with storage of spent nuclear fuel (the non-
23
reprocessing option). The UK and France have disputed the implications for reprocessing, but
the UK has accepted that operational discharges from Sellafield from reprocessing should have
fallen to zero by 2020.24
A number of other European countries have sent their spent nuclear fuel for reprocessing
abroad. However, this practice has largely ceased due to concerns about costs, the harm to
human health and the environment caused by the radioactive discharges, and the nuclear
25
proliferation risk associated with separated plutonium. Vitrified high-level wastes and plutonium
from past reprocessing are intended to be returned from the UK and France to the countries of
origin. However, the return of intermediate-level wastes will be limited.
In total, over 10,000 metric tonnes of spent nuclear fuel are being produced globally each year. The
global inventory of spent nuclear fuel is expected to more than double to over 445,000 metric tonnes
26
by 2020, with the highest percentage increases in developing countries. Yet, to date, no country has
27
achieved an effective solution for the long-term management of spent nuclear fuel.

12 September 2010
28
According to 2004 statistics cited by the IGD-TP, the annual production in the EU Member States of
radioactive waste and spent fuel considered suitable for deep geological disposal is 5,100m3 of long-
lived low- and intermediate-level waste (excluding that produced in Germany which is to be disposed
3
of in the Konrad mine), 280m of high-level waste and 3,600 tonnes heavy metal of spent fuel. At the
3 3
end of 2004, an estimated 220,000m of long-lived low- and intermediate level waste, 7,000m of
high-level radioactive waste and 38,000 tonnes of heavy metal of spent fuel were stored in Europe.
However, there are considerable uncertainties in these figures.
In reprocessing countries such as the UK and France, spent nuclear fuel and reprocessed plutonium
and uranium are not currently classified as nuclear waste, on the grounds that spent fuel is a
recyclable material and that reprocessed uranium and plutonium might be used to make fresh fuel.
This situation results in large volumes of radioactive material that may ultimately be buried in a
29
repository not being included in the official inventories of radioactive waste in these countries.
Plutonium (which is a nuclear weapons material) has no currently licensed disposal route and in
practice most separated uranium is not reused.
Spent nuclear fuel requires interim storage, to allow time for cooling after it is first removed from a
reactor during refuelling. Wet storage involves keeping the spent fuel rods in racks under water in
cooling ponds. Dry storage requires the use of casks designed to cool the waste by air convection
and to protect it from fires and mechanical impacts. Interim storage in Europe is normally at the
reactor sites or at centralised interim storage facilities; concerns about the safety of such facilities are
30
beyond the scope of this report. In countries with reprocessing plants, spent nuclear fuel, liquid and
vitrified high-level wastes and other radioactive wastes are stored at the reprocessing plant before
and after reprocessing. Even if repositories are established by the projected dates in Sweden and
Finland (the only countries which have so far selected sites), the amount of waste generated
annually will account for much of the quantity scheduled to be transferred annually to the repository:
hence it will take decades to reduce the amount of on-site radioactive waste significantly even once
31
repositories are constructed.
The focus of this report is on deep geological disposal of spent nuclear fuel and high-level nuclear
wastes from reprocessing, i.e. heat-generating wastes. Long-lived intermediate-level wastes from
reprocessing are also considered, but in less detail.
2.1. Harmful effects of radioactive wastes

Nuclear waste generates concerns because the radiation it emits (known as ionising radiation) can
cause cancer and other serious illnesses in humans, and harm other living organisms (see Boxes 3
and 4). High-level nuclear waste is so radioactive that exposure to it is deadly: high doses of
radiation cause skin burns, radiation sickness and death. Lower doses of radiation damage human
cells in a way that increases the risk of diseases such as cancer; the higher the dose the greater the
risk. If radioactive wastes leak from an underground repository they will expose people to low levels
of radiation which can harm health and the environment; the safety assessment for a repository is
required to take account of this.
Box 3: Radioactivity
The basic constituents of radioactive wastes are called radionuclides. These are atoms which
are unstable and change to other more stable forms in a process known as radioactive decay,
until a stable form is reached. The unit of radioactivity is the becquerel (Bq), defined as one
decay per second. The half-life is a measure of how quickly a particular radionuclide decays: it
is the time taken for the radioactivity to decay to half of its initial value. Different radionuclides
have different half-lives, varying from fractions of a second to millions of years.32
After the decay of a radionuclide atom, the remaining nucleus can be either stable (i.e. non-
radioactive) or unstable. If it is unstable, it will decay again: for some radionuclides long chains
of decays result as one atom changes to another and then another, emitting radiation at each
step.
When a radionuclide decays it can emit alpha, beta or gamma radiation.
Alpha radiation consists of two protons and two neutrons bonded together in a particle that is

September 2010 13
identical to the nucleus of a helium atom. It can be emitted when a heavy radionuclide decays.
Alpha particles are easily blocked (for example by a sheet of paper), but can be very dangerous
if they are emitted inside the human body (for example, from a radionuclide breathed into the
lungs, or ingested by eating or drinking contaminated food or water).
Beta radiation consists of high-energy electrons (or positrons). It is more penetrating than alpha
radiation and can penetrate living matter to some extent. However, it is less damaging, so the
same amount of exposure does less damage than exposure to alpha radiation.
Gamma radiation consists of electromagnetic radiation of very high energy. It is often produced
at the same time as alpha or beta particles, or at the end of a long chain of decays. Gamma rays
act like powerful X-rays which can pass through the human body, necessitating protection by
thick shielding (for example lead or concrete).
The harmfulness of radiation varies with the kind of radiation and its energy.
Box 4: Health effects of ionising radiation

33
The health effects of ionising radiation are not fully understood. The estimates of harm are
based mainly on the ongoing study of survivors of the Hiroshima and Nagasaki bombings in
1945, supplemented by some more recent studies (e.g. of the effects of medical exposures to
radiation and the Chernobyl accident).
People can be exposed to radiation either externally, when radionuclides decaying outside the
body expose it to ionising radiation, or internally if radionuclides are breathed in or swallowed
(for example, by eating radioactively contaminated food). Some radionuclides bioaccumulate:
i.e. they build up in the food chain, reaching higher concentrations in fish or seafood than in the
surrounding water, and thereby posing a risk of increased radiation dose to anyone eating the
contaminated food.
Radiation can cause genetic damage to cells. Sometimes this damage can be repaired by
mechanisms within the cell, but sometimes it can lead to the out-of-control growth of cancer
cells. Damage to eggs or sperm can be passed on to future generations.
Radiotoxicity is a measure of how harmful a radionuclide is to human health when inhaled or
ingested: it depends on the type and energy of the radiation emitted and the radionuclide’s
biochemical behaviour in the human body (for example, whether it is excreted quickly or builds
up in bones or organs). The harm that is done depends on the dose of radiation received. But
calculating this dose is not straightforward.
The absorbed dose (measured in grays or Gy) is defined as the average amount of energy (in
joules or J) that is deposited per unit mass (in kilograms or kg) of tissue from an exposure to
radiation. The effective dose (measured in sieverts or Sv) is calculated by weighting for how
harmful the type of radiation is thought to be (its estimated Relative Biological Effectiveness,
RBE) and the relative sensitivity to radiation of the organs in the body which are expected to be
exposed (e.g. lungs, liver, etc.). A sievert is the dose of a given type of radiation in grays that is
expected to cause equivalent damage in humans to 1 Gy of X-rays or gamma radiation: but this
is not known exactly.
The International Commission on Radiological Protection (ICRP) is an advisory body which sets
international standards on the calculation of doses and radiological protection.34
High-level radioactive wastes are so radioactive that the decay process generates significant
amounts of heat. They contain a wide variety of radionuclides, each with different physical and
chemical properties. Each radionuclide decays differently and has a different half-life. The physics of
radioactive decay is well understood, but the inventory of radionuclides in the wastes is not well
known. In addition, the chemistry of how wastes will behave in a repository is very complicated,
because each element can take different forms and form a variety of compounds: some of these
chemicals may dissolve easily and leak out of the repository in groundwater, while others may attach
to the backfill or the surrounding rock and thus be contained more easily. Some can also

14 September 2010
bioaccumulate in the food chain once they reach the living environment (known as the biosphere),
and each one may have different health effects on humans exposed to it. A few of these
radionuclides and their relevant properties are described in Box 5.
Box 5: Radionuclides and deep geological disposal

A chemical element is a pure chemical substance containing one type of atom. Each element
has a different number of protons in its nucleus – known as its atomic number. Isotopes are
atoms of the same element but having different numbers of neutrons. Unstable isotopes are
radioactive.
Actinides. The actinides are a series of elements with atomic numbers from 90 to 103 (thorium
to lawrencium, including uranium and plutonium). They are all radioactive and have a number of
different radioactive isotopes. Only thorium and uranium occur in significant quantities in nature.
Elements that are heavier than uranium are known as transuranic. Many actinide isotopes have
long half-lives (tens of thousands of years) and are also highly radiotoxic. They exist in large
quantities in spent nuclear fuel; successful containment of actinides is therefore very important
in the safety case for a geological repository.
Mobile radionuclides. Some radionuclides are expected to escape more easily from deep
repositories in significant quantities because they are highly mobile in groundwater and have
long half-lives, meaning that they are likely to reach the biosphere before they have decayed
and so pose a risk to living organisms. These are mainly negatively charged (anionic) species
(forms in which chemicals exist), which are not expected to be significantly retarded in the
backfill or the rock. The main radionuclides of concern are iodine-129 (129I, half-life 15.7 million
years), chlorine-36 (36Cl, half-life 300,000 years), selenium-79 (79Se, half-life 295,000 years) and
technetium-99 (99Tc, half-life 212,000 years).35 These radionuclides are less radiotoxic than the
actinides, but occur in large quantities in high-level radioactive wastes. Radioactive iodine that is
ingested by humans tends to concentrate in the thyroid gland, where it can cause thyroid cancer
and other problems. Technetium-99 bioaccumulates in the food chain, particularly in shellfish
36
such as lobster. Selenium is an essential micronutrient for many organisms and selenium-79
can also bioaccumulate in the food chain.
14
Carbon-14 ( C) has a half-life of 5,715 years and undergoes beta-decay into nitrogen-14. It is
relevant to radioactive waste disposal because it is the main radionuclide that might escape
from a repository as gas, in the form of carbon dioxide (CO2) or methane (CH4). In nuclear
wastes, carbon-14 exists mainly in irradiated metals (especially steels). Smaller quantities in
irradiated uranium can also impact on safety if the corrosion rate is high. There are particular
problems with carbon-14 in the UK inventory of intermediate-level waste from nuclear
reprocessing.37
Figure 1 shows how the radiotoxicity of spent fuel decays with time, on the basis of published
calculations for spent fuel from an LWR with a burn-up of 33 GWd per tonne of heavy metal, initial
enrichment 3.2% of uranium-235, and five years’ cooling.38 The radionuclide content and hence the
decay curve will differ for higher burn-up spent fuels and those from different reactor types.

September 2010 15
Figure 1: Decay in radiotoxicity of spent nuclear fuel
39
Adapted from Bombini et al. (2009).
1 – total radiotoxicity of spent nuclear fuel; 2 – plutonium and decay products; 3 – minor actinides and
decay products; 4 – fission products; 5 – uranium and decay products. 6 – (for comparison)
radiotoxicity of uranium ore. Units are Sieverts per million metric tonnes (Sv/Mt).

16 September 2010
3. The concept of deep geological disposal
Research on nuclear waste disposal began in the1950s but a concerted attempt to solve the problem
did not begin until the late 1970s.
In 1976 the influential Flowers Report, published by the UK Royal Commission on Environmental
Pollution, concluded that “There should be no commitment to a large programme of nuclear fission
power until it has been demonstrated beyond reasonable doubt that a method exists to ensure the
40
safe containment of long-lived radioactive waste for the indefinite future.” In April 1977, the Swedish
Parliament passed the groundbreaking Nuclear Stipulation Act (Villkorslagen) that reinforced this
standpoint by requiring the operators of nuclear power plants to have “proven how and where a
completely safe final storage facility” could be constructed for spent nuclear fuel or reprocessed high-
level waste before operating permission was granted. In the USA, the Interagency Review Group on
Nuclear Waste Management called for the development of geological repositories for high-level
41
nuclear waste disposal in 1979.
Since the adoption of these policies in the late 1970s, the focus of high-level nuclear waste disposal
has been on burying wastes underground. Other options – such as firing the waste into space in
rockets, burying it under the Antarctic ice sheet or dumping at sea – have been progressively ruled
out as unfeasible and/or unsafe. As a result deep geological disposal has dominated research
42
priorities for over 30 years.
The option of deep geological disposal would involve excavating a repository in rock, hundreds of
metres underground. The radioactive waste would then be put in containers which would in turn be
placed in deposition holes in tunnels in the rock. Tunnels would be backfilled to keep the containers
in place and to slow the release of radionuclides from the waste once the containers had corroded.
The site is supposed to be chosen so that the flow of water through the waste and back to the
surface would be slow enough for the radioactivity to decrease significantly before the living
environment above the repository could become contaminated. The release of gas from corroding
canisters and other structures, and radioactive gas from the waste itself, also needs to be
considered, as does the risk of future earthquakes or glaciation affecting the repository. The geology
of the chosen site and the engineered barriers around the waste are intended to be passively safe
(i.e. not to require human intervention) after the closure of drifts and shafts. However, some designs
would also allow retrieval of wastes should future generations decide to undertake this. The
geological disposal concept involves multiple barriers in an attempt to ensure the long-term
protection of the living environment.
The key stages for implementation of geological disposal are:
l establishment of the waste inventory
l development of concepts and technologies
l site selection and characterisation
l design of the deep geological repository
l safety demonstration based on scientific knowledge and demonstration of technology
l licensing
l construction and manufacturing
l waste emplacement
l backfilling and sealing
l final closure.
Siting a repository may take several decades and construction is expected to take another decade.
Final closure is expected to be at least several decades more after the start of the operational phase.
As well as the repository itself, encapsulation facilities would also be needed: here spent fuel or the
vitrified waste from reprocessing would be placed in canisters or overpacks. Long-lived intermediate-
level waste is often encapsulated in concrete or bitumen and may be placed in steel barrels.

September 2010 17
A transportation system would also be necessary to transport the highly radioactive wastes from the
interim storage facilities to the encapsulation plant and on to the geological disposal facility.
3.1. Safety assessment

Before a proposed repository can be licensed for use, a safety assessment must be produced and
approved by the relevant government regulators.
The IAEA manages the Joint Convention on the Safety of Spent Fuel Management and on the Safety
43
of Radioactive Waste Management. It has published guidance documents on the siting of geological
44 45
repositories and safety standards for their operation. The NEA has also developed guidelines for
46
the post-closure safety case.
The ICRP bases its recommendations on three fundamental principles – justification of exposures,
dose optimisation, and dose limits (which are not to be exceeded).47
The principle of justification requires that nuclear activities must be justified in the sense of doing
more good than harm. The ICRP states that “no practice involving exposures to radiation should be
adopted unless it produces sufficient benefit to the exposed individual or to society to offset the
detriment it causes”. This principle also requires the collective dose (the average dose for a group
exposed multiplied by the number of people in the group) to be weighed against the benefits of the
practice (such as the generation of electricity). The collective dose gives an indication of the number
of cancers and other adverse health effects that can be expected. Such cost-benefit analyses are
inevitably subjective but, importantly, the requirement to consider the collective dose is intended to
prevent the safety case being overly dependent on dilution and dispersion of radionuclides in the
environment.48 There is no known safe dose of radiation, and a high collective dose can arise if a
large number of people are collectively exposed to very low individual doses over time.
The ICRP has set a dose limit of 1 milli-Sievert (mSv) per year for exposure situations where
individuals received planned exposures from activities which are of no direct benefit to them
49
(unplanned activities – such as major nuclear accidents – might sometimes exceed such limits). A
lower ‘dose constraint’ is set as an upper bound on the predicted dose that is allowed from planned
future exposures such as that caused by waste leaking from an underground repository. For
prolonged exposure to gradually accumulating long-lived radionuclides from a deep underground
repository, the ICRP dose constraint is 0.1mSv per year (equating to a risk of death of one in a million
50
per year). However, the ICRP is an advisory body and in practice different countries have taken
different approaches to regulatory requirements. A 2007 review by the NEA found that dose
constraints set by individual countries span a range of 0.1–0.3mSv per year, while risk constraints are
51
set at one in 100,000 or one in a million per year. A major issue in the case of deep underground
repositories is whether these limits can be met in practice, due to the difficulties of predicting the
radiation exposures that will actually be experienced by future generations. Nevertheless the
regulatory system is intended to reflect key principles, including the concept of ‘inter-generational
equity’ or the idea that there should be no undue burden on future generations as a result of
52
producing nuclear electricity today.
The dose constraint is always lower than the dose limit and represents a basic level of protection
which sets an upper bound for a process known as dose optimisation. Optimisation is an iterative
process that involves the identification of possible protection options and the selection and
implementation of the best option under the prevailing circumstances. It is intended to ensure that
doses are ‘as low as reasonably achievable’ (ALARA), economic and social factors being taken into
53
account.
The most recent (2007) ICRP recommendations also expand the concept of radiological protection to
protection of the environment, including the maintenance of biological diversity, the conservation of
species and the health and status of natural habitats. However, the environmental impact of
radionuclides has only recently begun to be considered and the main focus of safety assessments
remains human exposures.
Safety assessment requires the post-closure behaviour of the radioactive wastes in a repository to be
predicted hundreds of thousands to millions of years into the future. The limitations of the computer
models that are used to make these predictions and the difficulties of validating them – i.e. of

18 September 2010
confirming that they will give sufficiently reliable predictions over such long timescales – are among
54,55
the key issues for safety assessment. Computer models of the evolution of the engineered
barriers and interaction between the multiple barriers have to be developed, to include all the
complex thermal, mechanical, hydrogeological, chemical, and microbiological processes which will
56,57
affect migration of the wastes as they are released from the containers. The release of radioactive
water and gas through the rock also calls for complex computer models, taking account of chemical
interactions with the rock, the transport of water and gas through cracks and fissures, and any
potential fast routes for escape, such as via the backfilled tunnels and shafts of the repository or
fractures and faults in the host rock.58,59,60 The effects of earthquakes (which can affect underground
water flow or damage packaging, even when they are not major events), long-term climate change
(which can alter sea level and underground hydrology) and the behaviour of future generations (who
might for example dig a well above the repository at some point in the future) also need to be
considered. Because many of the complex processes involved are poorly understood and many
model assumptions impossible to verify, the question of whether computer predictions are sufficiently
reliable to underpin a repository safety case is a matter of considerable debate.
The chemical conditions inside the repository are very important because they will influence which
chemical reactions can occur and at what rate. This in turn will affect the corrosion rates of the waste
containers, the properties of the bentonite clay expected to be used as backfill, and how quickly the
wastes dissolve and migrate through the backfill and rock. For example, corrosion of metals involves
61
both oxidation and reduction. Relevant chemical properties in a repository will include how acidic or
alkaline the groundwater becomes (its pH) during the lifetime of the repository and its redox
(reduction-oxidation) potential. Solutions with a pH less than 7 are said to be acidic and solutions
with a pH greater than 7 are said to be basic or alkaline. Reduction potential (Eh) is a measure of the
tendency of a chemical species to acquire electrons and thereby be reduced. Both Eh and pH
influence the type of chemical reactions that can occur. Eh-pH diagrams are commonly used in
geology for assessment of the stability fields of different minerals and dissolved substances: they
62
show under which conditions a mineral or chemical species is the most stable form. Understanding
and predicting the rate of the complex chemical reactions which will occur underground is central to a
robust repository safety case. However, many gaps in knowledge and uncertainties remain.
In order to meet the safety requirements, predicted doses to a ‘reference person’ living near the
proposed repository are supposed to be calculated many generations into the future. The habits used
as a basis for this calculation (e.g. consumption of foodstuffs and use of local resources) should be
63
typical of the small number of individuals expected to be most highly exposed. There are obviously
considerable uncertainties in defining these habits, as well as disagreements regarding the impacts
64
of radiation on vulnerable groups such as children, babies and developing embryos.
Because of the role that the geological surroundings are expected to play in containment of the
65
wastes, site selection is a key part of the safety case.
The inventory of wastes is also important because it determines the quantities of different
radionuclides, the chemical reactions that will take place, the volume of rock likely to be needed and
the amount of heat that will be generated by radioactive decay. Because high burn-up fuel contains
increased amounts of long-lived hazardous radionuclides in the spent fuel, such as americium,
curium and plutonium, for the same amount of energy produced, and generates significantly more
heat, the proposed use of high burn-up fuel in new nuclear reactors could have significant
66
implications for repository safety cases.
3.2. National programmes for geological disposal

Repository programmes are at different stages in various countries, and involve several different
approaches to containing highly radioactive wastes.67
To date, major problems with repository programmes have been encountered in several countries, for
example the UK, Germany and the USA (Box 6).

September 2010 19
Box 6: Existing difficulties with geological repository programmes
United Kingdom: A planning inquiry into a proposal to build the first stage (known as a ‘Rock
Characterisation Facility’) of a deep repository for long-lived intermediate-level wastes led to the
rejection of the plans in 1997. The planning inspector concluded that the site near Sellafield was
unsuitable for a repository for safety reasons.68,69,70 Various generic problems with deep disposal
and the site selection process were also highlighted in the rejection of the plans. Although the
proposal did not explicitly include high-level wastes, it was expected that the repository, if
approved, would have been expanded to include these in the future. Following the advice of the
71
House of Lords Science and Technology Committee (which reportedly advocated returning to
72
the site ), the UK Government subsequently changed planning law so that in future the scientific
evidence concerning safety at a site would not be cross-examined.73 It is now seeking volunteer
communities for a repository close to the original Sellafield site, with the intention of starting a
new programme to develop a repository which would accommodate high-level wastes and spent
nuclear fuel as well as intermediate-level wastes. A recent change in government may mean that
the planning process is revised again.
Germany: In Germany, the deep disposal concept has been based on the use of rock salt as the
host geological formation. From 1967 until 1978 the Asse II salt mine was used for disposal of
low- and intermediate-level radioactive wastes, including some long-lived wastes. In January
2010, the German authorities decided that all the waste from Asse II needs to be retrieved and
74
repackaged due to safety problems, including the leaking of saline water into the chambers. It
has not yet been decided where the waste will be stored. The costs of this expensive operation
will fall largely on German taxpayers. Repository shafts were constructed in 1985–90 in another
salt dome site at Gorleben, selected for disposal of spent nuclear fuel as well as high-level
waste from overseas reprocessing.75 However, in 2000 a moratorium was placed on activities at
Gorleben as a result of continuing concerns about the suitability of rock salt for geological
disposal. This moratorium was lifted in March 2010 to examine further whether Gorleben would
be a suitable site for the final storage of spent nuclear fuel.76 The target date for commencing
operation of a repository for spent nuclear fuel and high-level waste in Germany is still 2035, but
this does not appear to be in any way realistic.
United States: Yucca Mountain, Nevada was identified in 1987 as the sole US site to be
investigated for a high-level waste repository.77 Plans at Yucca Mountain differed from those in
other countries in that the waste was supposed to be placed above the water table, where it
would not be in contact with the groundwater that flows through most rocks. However, a major
concern was its siting in a geologically active area where there has been significant volcanic
activity and faulting. The programme was halted in 2010 after the Obama administration
announced that a new plan would be developed.78
Currently active programmes are mainly limited to two different approaches: the first developed by
the Swedish Nuclear Fuel and Waste Management Company (SKB), and the second largely by the
French nuclear waste management company ANDRA. The Swedish approach involves the disposal
of spent nuclear fuel in copper canisters in crystalline rock (Box 7). The French approach involves the
disposal of vitrified high-level waste in steel overpacks in clay rock formations (Box 8).
Finland and Sweden plan to start operating deep geological repositories for direct disposal of spent
nuclear fuel in 2020 and 2023 respectively, following the Swedish deep repository concept. Canada
and South Korea intend to follow a similar approach, as does the UK for disposal of unreprocessed
spent nuclear fuel from new nuclear reactors.
France plans to start operating a deep geological repository for vitrified high-level waste from
reprocessing in 2025. Belgium and Switzerland are also investigating a similar approach using clay
host rocks.

20 September 2010
79
Box 7: The Swedish concept
In the Swedish concept for a deep geological repository, spent nuclear fuel will be placed in cast
iron frames surrounded by 5cm thick copper canisters. The canisters will be deposited in granite
bedrock at a depth of 500m and surrounded by highly compacted bentonite clay.
Once the repository is closed, groundwater will come into contact with the canisters containing
the wastes. The copper canisters are expected to corrode very slowly in the absence of oxygen:
the target lifetime for containment of radioactive waste in the canisters is 100,000 years.
The bentonite and surrounding crystalline bedrock are water-conducting, so the only absolute
barrier to radionuclide migration will be the copper canisters, for as long as they remain intact.
Once the canisters have corroded, radionuclides are expected to leak into the surrounding
water. The bentonite clay is intended to act as a chemical buffer, slowing the movement of some
radionuclides, particularly the highly radiotoxic actinides (see Box 5). It also gives the canisters
mechanical support, as it swells in water.
The bentonite clay and bedrock are expected to slow the movement of radionuclides to the
biosphere. However, absolute containment until the waste has decayed is not expected and
some of it will migrate to the surface in groundwater or as gas.
Once radionuclides are close to the surface, the safety case relies on their dilution and
dispersion in the aquifer above the repository and in the biosphere to limit the doses that
humans receive through drinking or eating contaminated water or food.
80
Box 8: The French concept
The French concept for deep disposal differs from the Swedish one in two main respects. Firstly,
the rock type will be clay, not crystalline; secondly, vitrified high-level wastes will be placed in
steel overpacks rather than copper canisters. Steel is expected to corrode more rapidly than
copper, so the safety performance of the repository will be more reliant on the surrounding
bentonite and clay rock.
Russia has been investigating the feasibility of salt, granite, clay and basalt as possible host rocks for
geological repositories, but has no projected date for completion of a repository. China is
investigating five potential repository sites, including a proposed underground research laboratory
site in the Gobi desert, but is not expected to have an operational disposal facility until 2040 at the
81
earliest.
In Finland a disposal site has already been selected at Olkiluoto. In Sweden a site has been selected
at Forsmark, on the east coast. In France the zone for disposal – the village of Bure in Lorraine – has
been selected and the final site is to be specified by 2013. The Swedish, Finnish and French
proposals are therefore the main focus of the remainder of this report.
3.3. Potential for significant radiological releases?

A number of low- and intermediate-level radioactive waste disposal sites have operated over the last
50 years. However, many of these supposedly final disposal sites have already caused unexpected
environmental contamination, highlighting how difficult it is to predict what will happen to buried
wastes, even over short timescales. Examples are the Dounreay nuclear waste shaft in Scotland,
which exploded in 1977,82 the Centre de Stockage de la Manche storage site in France, where water
83 84
supplies in the aquifer have become contaminated, and the Asse II salt mine in Germany (see Box
6). Moreover, the disposal of high-level wastes raises unprecedented challenges because of the very
long half-lives and radiotoxicity of these wastes.
Enthusiasts for deep geological disposal argue that there are examples (known as natural
analogues) which demonstrate that geological formations are capable of isolating highly volatile and
flammable substances such as oil and gas underground for hundreds of millions of years.85
Concentrated natural uranium deposits have been largely confined for millions of years at sites such

September 2010 21
as Cigar Lake in Canada, and there is even an example of a natural underground nuclear reactor
86
containing uranium and fission products in Oklo, Gabon.
However, the emplacement of high-level waste in an underground repository would entail a major
perturbation of the geological system, involving:87
(i) a large number of tunnels covering an area of several square kilometres
(ii) the release of significant amounts of heat, initially of the order of tens of thousands of
kilowatts per square kilometre
(iii) intense radiation and significant quantifies of highly toxic radionuclides, each with its own
complex chemistry.
Nuclear Waste Advisory Associates, a UK-based consultancy, has listed over a hundred scientific
and technical issues that remain to be resolved in relation to producing a robust safety case for the
88
deep disposal of radioactive wastes. Significant releases of radioactivity from an underground
repository could occur if the near-field or far-field barriers were breached in ways that allowed
radioactive groundwater or gas to escape faster than expected.
The current state of knowledge about these issues is considered in the literature review that follows.

22 September 2010
4. Literature review of post-closure issues
4.1. Corrosion of canisters, wastes, and repository structures

Copper or steel canisters or overpacks will be used to contain the spent nuclear fuel or high-level
waste when it is placed in the repository. As groundwater from the surrounding rock flows into the
repository, these canisters or overpacks will begin to corrode and eventually their radioactive
contents will be released into the groundwater.
The focus of this report is on the Swedish and French designs in which the waste is below the water
table and the backfill is expected to become saturated with water soon after the repository is closed.
In the USA, the Yucca Mountain proposed site (now abandoned) was above the water table.
However, rainwater was still expected to enter the repository and to cause corrosion.89,90
The Swedish safety case assumes that copper canisters 5cm thick will contain the wastes for
100,000 years, but there are serious question marks about the assumptions that have been made
regarding the low corrosion rate of copper91 (discussed further below). Steel is expected to corrode
much more rapidly than copper: with a typical design life of 1,000 years. Actual life may be
significantly longer than design life and the predicted lifetime of the steel overpacks is of the order of
10,000 years.92 However, the safety case for the French approach remains much more dependent
than its Swedish counterpart on the performance of the clay backfill and bedrock, due to the faster
corrosion of steel.
An inner material is also needed between the insides of the canisters and the spent fuel assemblies
they contain, to prevent the gap filling with water and a criticality (nuclear chain reaction) from
occurring. A cast iron insert will be used in the Swedish copper canisters; other materials (for
example, glass or depleted uranium), each of which has different advantages and disadvantages,
93
are being considered as possible alternative inserts in steel canisters in other countries.
Corrosion of steel, and perhaps of copper, will release hydrogen gas into the repository. Corrosion of
some wastes can also release carbon dioxide or methane, which may be radioactive (containing
carbon-14). The build-up of gas pressure could be harmful, since a sudden release of pressure (or
explosion) could damage the repository. Alternatively, slow release of gas could open up fractures in
the backfill or rock, and speed up the release of some radionuclides from the repository.94
These issues are discussed in more detail below.
4.1.1. Corrosion of copper

The Swedish concept for deep disposal uses copper canisters because the corrosion rates are
expected to be extremely slow. The corrosion behaviour of copper canisters is expected to change
with time as the conditions within the repository evolve from warm and oxidising initially to cool and
95
anoxic in the long term. Copper corrodes in air due to the presence of oxygen, forming copper
oxides. There will be air in the repository during the decades when it is operational (i.e. while the
waste is being emplaced). However, after the repository is closed, safety cases assume that all the
oxygen will be rapidly used up by the metabolism of oxygen-using microbes (aerobes) and other
chemical reactions, so that the copper canisters can no longer corrode in this way.
Nevertheless, there remains concern about the rate of corrosion of copper during the first 100 years
or so, when oxygen and heat are both likely to be present. In Canada, coating copper canisters with
a polymer is being considered as an option to provide protection during this early emplacement
96
phase.
After all the oxygen has been consumed, it is assumed that sulphide will be the primary corrosive
agent for copper canisters in a repository, and corrosion will proceed with the formation of copper
97,98,99
sulphide and hydrogen gas, although corrosion rates are predicted to be very slow.

September 2010 23
In general, it is presumed that the canisters will corrode in a uniform way, rather than through
localised corrosion such as pitting.100,101 However, in reality, pitting may also occur and one of the
102
scenarios that may result in early release of radioactivity is water flow into a defective canister.
4.1.2. Corrosion of copper by water

It has long been assumed that water alone does not corrode copper in an oxygen-free environment. If
this assumption is wrong, the copper canisters used in the Swedish deep repository concept could
corrode much more quickly than the current estimates suggest. The Swedish scientist Gunnar
Hultquist first questioned this assumption in 1986, when he measured an increase in hydrogen
103
concentration in the gas volume above copper in water. The results of his experiments are open to
question due to problems with the probe used to measure hydrogen pressures. Nevertheless, an
additional experiment published in 1989 supported the initial findings.104 These experiments have now
been repeated: the researchers conclude that the results show that copper corrodes in water free of
105
dissolved oxygen, forming a hydrogen-containing corrosion product. The hydrogen produced by
corrosion in pure water is apparently found in the metal, the corrosion product and the water as well
106
as in the gas phase. If this conclusion is correct, it has serious consequences for the repository
safety case: calculations based largely on observations of corroded copper coins recovered from the
Swedish Vasa warship, which sank in 1628, suggest that the copper canisters would need to be more
107
than 1m thick, rather than 5cm, in order to last 100,000 years.
One response to the experiments suggests that corrosion of copper by pure water alone cannot
occur and that there is an alternative explanation for the measurements: namely that the hydrogen
evolution observed was caused, not by the reaction of liquid water with copper but by the reaction of
adsorbed water with the stainless steel walls of the vacuum container in which the experiment was
conducted.108 Further, supporters of the Swedish safety case argue that the coins from the Vasa ship
109
may have corroded because the water was polluted by sewage and contains hydrogen sulphide.
110,111
However, the original authors disagree and have defended their findings. Other authors have
suggested that the Eh-pH diagram for copper may differ from that currently assumed in the safety
case, adding weight to the experimental evidence of Hultquist and colleagues that the corrosion of
112
copper in water is not fully understood.
In 2009, the Swedish National Council for Nuclear Waste (Kärnavfallsrådet) held a seminar to
discuss this dispute. The report of the seminar includes the views of experts on the findings to date
113
and on additional research that should be conducted.
4.1.3. Role of microbes

It has been known since the 1980s that microbes might survive in a deep geological repository and
114
that the effects of microbial activity could have profound impacts on waste containment. In 1987,
115
microbiology became a part of the Swedish scientific programme for deep disposal. Microbes could
have a number of adverse effects on the safety of a nuclear waste repository, including causing
corrosion of metal waste containers.
There is now little doubt that life could survive in a repository in the form of microbes, despite the heat
and radioactivity generated by the wastes. In experiments conducted in Canada’s Underground
Research Laboratory, culturable populations of microbes were found at all locations studied in the
bentonite-based sealing materials.116 The microbes included heterotrophic aerobes, anaerobes and
sulphate-reducing bacteria (SRB). (A heterotroph is an organism that cannot synthesise its own food
and is dependent on complex organic substances for nutrition.) The microbes identified were more
abundant at interface locations and absent only in those samples affected by heat and extreme
drying (desiccation). Aerobic populations (those requiring oxygen) were significantly higher in the
interface environments, especially at the rock–bentonite interface. Conditions in the backfill region
also appeared to be conducive to microbial activity, causing a reduction in oxygen, followed by a
decline in aerobic populations and an increase in anaerobic populations (ie those not requiring
oxygen, including SRB). The viable population was considerably larger than the culturable
population, suggesting potential for future increased activity if conditions became more favourable.

24 September 2010
Increased heat (and possibly some radiation) was found to increase nutrient availability in bentonite-
based materials and to have a stimulating effect on microbial activity.117 Migration of micro-organisms
through the bulk of the buffer appeared to be slow, but migration along the metallic holder–buffer
interface was rapid, suggesting that cracks or interfaces may form preferred pathways for
migration.118 The buffer used in the experiments was a mixture of sand and clay, rather than 100%
bentonite. However, other experiments conducted in Sweden have found that the sulphate-reducing
bacterium Desulfovibrio africanus is present in commercially available bentonite, and survives and is
viable after exposure to high salt concentrations (which may occur in groundwater at depth) and
119
temperatures of 100ºC for 20 hours. SRB are also a characteristic component of the Opalinus Clay
formation, investigated as a potential repository host rock in Switzerland.120
SRB reduce sulphates to sulphides. Sulphides react with copper and could potentially corrode
copper canisters in a repository. However, extrapolation from underground experiments suggests that
121
the reaction rate is too low to significantly reduce the predicted lifetime of the canisters.
In concepts where the repository is to be kept open for a long period of time, to allow for monitoring
and possible retrieval of wastes, there may be added difficulties with microbes due to the presence in
the ventilated caverns of a humid, oxygen-filled environment. This could provide many potential
niches for microbial growth, which could then affect the integrity of the storage canisters.122
4.1.4. Steel corrosion and hydrogen gas generation

In a deep repository, hydrogen will be produced by anaerobic corrosion of iron. In the French
concept, iron will be present in the steel overpacks for the vitrified high-level waste. In the Swedish
concept, the canisters will contain iron, which will be exposed only once the copper has been
corroded or damaged. Hydrogen can also be produced by radiolysis (the dissociation of molecules
by radiation) of the organic waste contained in some waste packages: for example, in the long-lived
intermediate-level wastes generated by reprocessing in the UK and France. If copper corrodes in
water alone, as some evidence has suggested (see Section 4.1.2), hydrogen may also be produced
123
by this reaction.
The corrosion rate of iron and steel may be significantly increased by the presence of gamma
radiation. Experiments involving the measurement of hydrogen produced by corroding steel in
artificial groundwaters suggest that the corrosion rate could be increased 10- to 20-fold in bentonite-
equilibrated groundwater exposed to high levels of gamma radiation.124 The reasons for this are not
fully understood.
The pressure rise in a repository due to the formation of dissolved hydrogen, and the subsequent
production of gas bubbles, might be sufficient to break or fracture the barriers (this is discussed
further in Section 4.2.5). Hydrogen embrittlement of the corroding metal might also occur, with
125,126
detrimental effects on the mechanical characteristics of the overpacks or canisters.
4.1.5. Creep
Creep is the tendency of a solid material slowly to move or deform permanently under the influence
of stresses. Creep in copper occurs readily at the high temperatures expected in a nuclear waste
repository. In safety assessments calculations are necessary to show that the canisters will not
rupture under the stresses to which they will be subjected. Calculations based on a creep model of
the Swedish deep disposal canisters under the pressure and temperature conditions expected in the
repository suggest that there will be very high stresses at the edges of the canisters, where creep
rates will therefore be high, and that the cylindrical canisters will distort to an hour-glass shape in the
repository due to elastic and creep deformation. However, the creep strain at the edges is still
expected to be less than would be needed to rupture the canisters.127

September 2010 25
4.1.6. Summary of corrosion issues
The mechanisms for corrosion – including the role of bacteria – are not fully understood. This could
result in both copper canisters and steel overpacks corroding more quickly than expected, allowing
faster than predicted release of radionuclides into groundwater. A key issue is whether copper
canisters corrode in water in the absence of oxygen: if so, their design life has been significantly
overestimated. The intense radiation in the repository is also likely significantly to increase the
corrosion rate of steel.
4.2. Bentonite erosion and loss of buffer capacity

The bentonite surrounding the canisters or overpacks is expected to provide physical support and to
influence the chemistry of the repository, acting as a buffer and slowing the movement of some
radionuclides – particularly the highly radiotoxic actinides. However, a number of physical and
chemical processes can affect bentonite in ways which could compromise safety.
Groundwater transport through bentonite remains poorly understood, with diffusion probably taking
place through the interlayers of clay particles.128
4.2.1. Effects of heat and mineral changes on bentonite

The heat from the high-level waste in the repository will heat up the buffer/backfill and the
surrounding rock of the different repository tunnels over a period of several decades as they are
successively filled with the waste.129 The different components in a repository all have different
expansion coefficients and the way they move and compress may lead to a significant change in the
hydraulic properties of the interfaces between them. Heating could also cause significant pore
pressure changes, particularly in clay rock, affecting the stress distribution, which could in turn
damage the structure of the clay rock so that water flows through it more easily. Furthermore, the
heat could induce convective flow of groundwater in the surrounding rock, along with significant
vaporisation of groundwater, which may be ventilated in the pre-closure stage. This phenomenon
complicates the prediction of how conditions in the repository will change with time, since the effects
of water vapour as well as liquid water need to be considered.
Experiments show that predicting the combined effect of heating and wetting on the bentonite
requires coupled thermo-hydro-mechanical models.130,131 Complex interactions need to be included in
these computer models, such as the effects of the wetting and swelling of the bentonite on water, gas
and thermal flows and the effect of the changing thermal gradient on the transport of water vapour in
the bentonite.
Once the repository is sealed, there will be no escape of moisture and the excavated cavity will
become re-saturated with groundwater, causing the bentonite to swell.132 The temperature will build
up to a peak, which will be reached after some decades near the canister but may take hundreds of
years in the far field. This is also the period when the hydraulic pressure will be rebuilt in the
backfilled and sealed repository opening. Thermally induced flow or convection and coupled thermal-
mechanical processes will last much longer than the temperature pulse and could peak at about
10,000 years.
The heat in a repository could have a significant negative impact on the properties of clay. The
bentonite clay intended to be used in repositories consists mainly of montmorillonite, which is a
member of the smectite group of minerals. Smectite is considered to be a good buffer material
because it swells in contact with water – slowing groundwater flow and also holding the waste
canisters firmly in place – and because it can retain radionuclides by sorption (a process in which
they become incorporated in, or stick to, the clay particles). The swelling bentonite is expected to
133
exert a swelling pressure on the canisters of up to 15MPa, generating considerable stresses (see
Section 4.1.5).
The high-level waste placed in a repository is expected to increase temperatures considerably until
its radioactivity has decreased significantly. When smectite clay is exposed to high temperatures and

26 September 2010
the geochemical conditions of a repository for a long time it could be transformed into other minerals
with different physical and chemical properties.
Smectite is converted to illite – a clay-sized but non-expanding mineral – in a reaction which
becomes faster as the temperature increases. There are two possible chemical reactions, which
depend on the chemical conditions. Experiments conducted in South Korea found that smectite
134
transforms into randomly interstratified illite–smectite layers, and eventually into illite. The
experiments showed that this reaction can affect the barrier properties of smectite clay which are
required for a repository. When the temperature in the experiment increased (from 90ºC to 200ºC),
the percentage of the expandable smectite layers in interstratified illite–smectite decreased and its
sorption capacity was very significantly reduced (with a decrease in sorption distribution coefficient
135
Kd of more than 90% for the caesium and nickel ions tested).
The Swedish repository concept currently assumes that the negative effects of illite production can be
limited by spacing the spent fuel canisters far enough apart to keep temperatures to less than 100ºC.
However, the rate of conversion of montmorillonite to illite is in fact not yet known, and other
mineralogical changes can also take place which are not yet well understood.
A geological site where bentonites occur naturally at Kinkulle in Sweden suggests that a reduction of
50–75% in the proportion of montmorillonite may have taken place over about 1,000 years, at
temperatures estimated to have reached a maximum of 150ºC; this may imply much quicker changes
136
in a repository than has been assumed, which could have serious implications for the safety case. A
data synthesis reports that experiments at temperatures lower than 100ºC have also identified
significant changes in the buffer: these include drops in swelling pressure of more than 50% in a
Czech experiment, and a hundredfold increase in hydraulic conductivity (due to changes in particle
structure) found in an experiment conducted in SKB’s underground laboratory.137 The most obvious
change observed in experiments is the dissolution of minerals such as calcite and feldspar, which are
present in the clay, but dissolution of montmorillonite also occurs. This happens in all experiments in
a large part of the buffer. Precipitation of iron and silicon then welds the stacks of clay particles
together, giving rise to a permanent increase in hydraulic conductivity and a drop in sealing pressure
– meaning that water flows more easily through the heat-damaged clay, which loses its important
sealing properties. A more detailed analysis of the Czech experiments suggests that the typical radius
of the larger pores (macropores) in a mixture of 85% bentonite, 10% sand and 5% graphite increases
threefold at 85ºC. The authors suggest that the observed microstructural changes in the experiment
can be explained by mineralogical transformations, which have a serious impact on the geotechnical
properties of the bentonite-based mixture.138
Altered mineralogy may also impact on other properties of the clay. For smectites, the risk of failure
due to creep (the deformation of the clay under long-term strain, such as the weight of the canisters)
is believed to be very small, with canisters expected to sink only a very small distance – of the order
139
of 10mm – over a million years. The drop in sealing pressure in heat-damaged clay observed in the
Czech experiments might affect this, although the author of this report is not aware of any in-depth
studies of creep in heat-damaged clay.
Because of the expected adverse impacts of heat on bentonite clay, SKB has developed thermal
design criteria based on an upper temperature limit of 100ºC. The maximum expected bentonite
temperature is a function of the thermal properties and geometry of the bentonite barrier, the thermal
properties of the surrounding rock mass and the deposition geometry, i.e. the spacing between
individual canisters and between tunnels. SKB has developed a computer model to predict maximum
140
temperature based on these parameters. It has also conducted heating experiments in the Äspö
Hard Rock Laboratory and used ‘inverse modelling’ to try to calculate the thermal conductivity of the
rock, on the basis of how the temperature changes.141 Uncertainties in the predictions appear to be
dominated by spatial variability in the thermal properties of the rock. Some of the experimental
measurements also appear to be influenced by groundwater movements. Allowing a margin of error,
these studies can be used to determine the spacing of canisters that will be needed to meet the
142
100°C temperature limit.
The spacing of the canisters is one of the parameters with most impact on the size and cost of a
repository (see Section 5.3). If the maximum temperature limit were lowered in order to meet

September 2010 27
concerns about the effects of temperatures below 100ºC on bentonite this could significantly increase
costs and make it more difficult to dispose of a given quantity of waste in the available volume of
bedrock at a potential repository site.
Heating can also release gases from clay host rocks. In a study performed in the Opalinus Clay in
Switzerland, carbon dioxide and hydrogen sulphide were the most prominent gases released, both of
which could interact directly with waste containers or wastes and/or change the chemical conditions
143
in a repository. In the experiment, the clay rock in the test field was found not to be gas- tight.
4.2.2. Effects of saline water

The salinity of groundwater can also affect the properties of bentonite. In experiments, mineral
alteration of bentonite due to the accumulation of magnesium occurred in saline water at
temperatures of 60°C and 90ºC. The cation exchange capacity (CEC) decreased as the amount of
magnesium increased – presumably due to occupation of the internal surfaces – and the distribution
coefficient Kd for caesium in the altered bentonite was half that in the original, suggesting that the
144
thermal alteration of bentonite in saline water affects the caesium sorption capacity. Caesium-137
was used in the experiment, as a chemical analogue for caesium-135, which has a much longer half-
life and is considered to be one of the most important radionuclides in the safety assessment for a
Japanese repository. The precipitated magnesium may also prevent the swelling of the bentonite.
The CEC is a measure of the quantity of positively charged ions (cations) the clay can hold, so a
reduced CEC combined with a higher hydraulic conductivity is likely to mean faster escape of some
radionuclides.
Preliminary experiments conducted in Spain show that swelling induced by the dissolution of salt
145
crystals in clays may be significant in saline groundwaters.
4.2.3. Effects of other minerals in clay

Bentonite clay can also contain other minerals such as carbonates, quicklime, apatite and oxides.
These minerals can be formed and dissolved in the matrix. For example, various sizes of carbonate
nodule are found in bentonite mines, forming and dissolving as conditions change, and potentially
creating large pores or gaps in the clay. Studies in Japan have shown that these minerals can be
dissolved in acid, potentially opening spaces in the rock. However, this process may not be similar to
what happens in nature.146
4.2.4. Chemical disturbance due to corrosion

Bentonite is expected to be well-buffered, leading to stable pH conditions in the repository backfill.147
However, chemical disturbance due to corrosion could change the properties of the backfill.
In the French repository concept, steel overpacks rather than copper canisters are expected to be
used. The interactions between the corrosion products of steel, the surrounding groundwater and the
bentonite are expected to create a chemical disturbance inside the engineered barrier system.
Modelling of the system over 100,000 years predicts that the porosity of the bentonite will increase,
due to changes in its mineralogy, and that both the Eh and pH will change significantly. However, the
model suggests that there will be a feedback effect, involving the clogging of pores in the clay near
each steel overpack, which will slow the initial high corrosion rate and its influence on the
148
mineralogy.
Iron frames used for spent fuel (which are to be contained inside the copper canisters in the Swedish
design) will also create a chemical disturbance in the same way. The incorporation of corroded iron
into clay can in theory act as a pump to accelerate corrosion. A UK model again shows slowing of
corrosion after time due to clogging of pores in the clay, but the chemical reactions assumed to take
place differ significantly from the model developed in France. The authors conclude that meaningful
application of the model requires key missing data, such as solubilities and free energies at the
mineral–fluid interface. In addition, the chemical reactivity of hydrogen gas (which is assumed to be

28 September 2010
inert and diffuse away into the rock) may need to be taken into account.149 Experiments suggest that
high concentrations of iron ions can be reached in bentonite without any mineralogical
transformations but that CEC and swelling pressure may be reduced and hydraulic conductivity
150
increased. As with magnesium accumulation (see Section 4.2.2), a reduced CEC combined with a
higher hydraulic conductivity is likely to mean faster escape of some radionuclides.
Large quantities of cement are also expected to be used in the repository for construction and
sealing. The highly alkaline cement pore fluid may have adverse effects on bentonite, significantly
151
reducing its swelling pressure and CEC. A number of minerals are expected to form as a result of
cement-bentonite interactions and computer models of this process have been developed.153 The
152
creation of highly alkaline fluids is expected to degrade the clay rock at the interface with the barriers
in the French repository concept, and concrete engineered barriers may also be susceptible to attack
by groundwater containing dissolved sulphates.154
4.2.5. Effects of gas on the clay barrier

Corrosion of steel in the repository would lead to the generation of hydrogen gas in the backfilled
tunnels, which could seriously affect repository safety if pressure build-up were to force fast routes
through the bentonite or host rock or explosively damage their structure.
Four principal mechanisms have been identified by which gases can pass through clay barriers:155
l two-phase (water plus gas) advective flow (i.e. due to bulk motion through the rock), under the
control of a combination of capillarity (the pull through the clay pores due to the attraction of
molecules to the clay) and hydraulic gradient (difference in pressure)
l diffusion of gas through intervening fluid to neighbouring voids in the clay with lower gas
concentration
l deformation of the clay, creating larger pores to accommodate gas flow
l fissuring and fracturing caused by gas breakthrough if the gas pressure becomes too high
(i.e. if it does not dissipate fast enough through the other mechanisms).
Gas breakthrough is considered to be a serious potential problem as it could permanently damage
the engineered barriers and surrounding rock. Diffusion is expected to be limited through the highly
compacted clay. Experiments and computer modelling have therefore focused on demonstrating that
gas could escape through advective flow before the gas pressure built up sufficiently to cause
fissuring. However, advective flow could also have safety consequences because water would be
pushed through the clay ahead of the gas. Advective gas flow could therefore speed up the transfer
of radionuclides to the surface once groundwater had become contaminated (i.e. when the canisters
or overpacks had corroded sufficiently to expose the wastes): this issue is considered further in
Section 4.4.3.
The mechanisms for gas breakthrough appear to be strongly dependent on the conditions of the
156
tests. Gas breakthrough in bentonite is often abrupt, perhaps indicating channelling of gas or
fracturing. In illite, the gas breakthrough pressure appears to be lower and less clearly defined:
breakthrough seems to develop sequentially through many flow channels. Increased resistance to
breakthrough can come from either an increase in saturation or an increase in clay density: the key
consideration is the openness of potential flow channels. Above a certain degree of saturation
(estimated at 93% in pure bentonite), breakthrough pressure rises sharply. Breakthrough is at least
partly time-dependent and can occur at low pressures after a long period of time.
Modelling has suggested that hydrogen gas breakthrough could occur in the conditions expected in a
repository following the French concept (i.e. using steel overpacks or canisters) and that the gas
problem is a key issue for the long-term performance of the clay barrier and hence for disposal
157
safety. Hydrogen gas will form at the interface between the steel and bentonite and this could lead
to over-pressurisation (gas build-up). Preferential pathways could form through fissuring of the rock,
but could be closed again by the self-healing properties of clay, leading to a cyclical process in which
158
the gas pressure again built up. However, a more recent model that includes feedback

September 2010 29
mechanisms suggests that the degree and physical extent of gas pressure build-up may be much
159
smaller than earlier models found. In this model, the gas pressure increases initially at the canister,
but later decreases and eventually returns to a stabilised pressure that is slightly higher than the
background pressure.
In the Swedish repository concept, it has been assumed to date that corrosion of copper in the
absence of oxygen will not occur and that the design life of the copper canisters is 100,000 years. If
these assumptions are correct, hydrogen generation will be limited until the iron inside the copper
canisters is exposed much later in the lifetime of the repository. If however corrosion of copper by
water can occur in the absence of oxygen (see Section 4.1.2) the hydrogen generated by this
reaction might also have significant implications for the safety case; however, the author of the
present report is not aware of any studies that have attempted to quantify this.
Additional steel may be introduced into a repository for other reasons, e.g. as structural support
during excavation (necessary to keep structures open in the case of clay rocks160); or in the form of
steel barrels containing long-lived intermediate-level wastes. Hydrogen generation from the corrosion
of this steel also needs to be considered in the safety case.
4.2.6. The role of microbes: gas production and biomineralisation

Microbes can corrode compacted bentonite, but current models suggest this would occur very slowly
(at a rate of a few millimetres in 10,000 years).161 Nevertheless, other potential effects of microbes on
the backfill, in particular their alteration of the mineral composition of bentonite or their generation of
162, 163
gases, may have significant implications for a repository’s safety case. Microbes can both
164
produce and consume gases and microbial gas production could cause a build-up of gas in a
repository, potentially reducing the effectiveness of the clay-based barrier. The generation of carbon
165
dioxide and other gases could also enhance radionuclide solubility and transport. Microbial
processes could in addition affect adsorption/precipitation of radionuclides, chemical conditions and
the creation of colloids (see Section 4.3.2).
At the Severnyi repository of intermediate-level liquid radioactive wastes in Siberia, Russia, injection
of waste has been shown to stimulate methane and hydrogen sulphide production by microbes,
which existed at all depths investigated (up to 405m).166 Experiments in the Canadian Underground
Rock Laboratory have shown that the production of gas (methane) in backfill is possible and could
167
occur in the prevailing chemical conditions. The 1996 FEBEX experiment found that significant
amounts of hydrogen, carbon and hydrocarbons were formed due to either thermal or microbial
168 3
decomposition in the bentonite. More than 0.35m of carbon dioxide per 100kg of bentonite was
formed, which may indicate that the gas could enhance the transport of radionuclides and micro-
organisms. The gas could also have a significant impact on the permeability of the buffer material by
disrupting its mechanical structure, e.g. by increasing the size and frequency of the clay pores in the
bentonite near the canisters, and hence its permeability.
Microbial degradation of organic material within radioactive wastes, the main component being
cellulose, can lead to generation of gases: this was a particular issue for the UK Nirex safety
assessment programme due to the inclusion of large quantities of cellulose in the intermediate-level
169
wastes destined for the proposed repository at Sellafield. Degradation products of cellulose can
also enhance the solubility of radionuclides such as plutonium.
Bacteria often play an important role in the production of minerals in a process known as
biomineralisation.170 Depending on the conditions and micro-organisms available, biomineralisation
can clog pores in rock by means of precipitation or enhance permeability due to decreased solid
content.171 The conversion of montmorillonite to illite in the bentonite backfill (or surrounding clay
rock) may have significant impacts on a repository’s safety case, as described above (Section 4.2.1).
Findings that micro-organisms can dissolve smectite at room temperature (by reducing Fe(III)) have
been described as a major challenge in the context of deep geological disposal, since they suggest
172
that this process may happen much faster than predicted, even in the absence of significant heat.

30 September 2010
4.2.7. Summary of bentonite erosion and loss of buffer capacity
The effects of intense heat on the bentonite backfill of a repository could seriously damage its ability
to trap some radionuclides. Chemical and physical disturbance due to corrosion, gas generation and
biomineralisation could also adversely affect the properties of the bentonite backfill.
4.3. Solubility, sorption and transport of radionuclides

4.3.1. Geochemistry and buffer chemistry
The longer it takes for a given radionuclide to diffuse across the clay buffer, the lower the rate of
release of that radionuclide from the near-field engineered barrier system will be, thanks to
173
radioactive decay. Radionuclides released from the waste will precipitate when their concentrations
in the pore water exceed their solubility in the water. This will limit the concentrations of many
radionuclides in the buffer and thus their release rates to the surrounding rock.
The chemical conditions of the buffer are expected to delay significantly the release of some
radionuclides but not others. For example, in the French safety case, the mobile radionuclides
chlorine-36, iodine-129 and selenium-79 are assumed to be non-sorbing in the clay rock, and are
consequently expected to be the only three radionuclides that enter the biosphere during a million-
year timeframe (although it is possible that the solubility of selenium may be reduced by other
174
complex chemical mechanisms).
In contrast, the release of actinides, such as plutonium, is expected to be delayed by the chemical
properties of the buffer. Thus the thickness of the buffer is expected to have a major impact on the
release of relatively short-lived actinides, such as plutonium-241 (formed by the decay of curium-
245) and plutonium-239.175 However, the effectiveness of the buffer will depend on the chemical
conditions (such as pH and Eh) and also on the physical and chemical form of the radionuclides.
The speciation of radionuclides is the distribution of a radionuclide among different chemical
species in a system. Species are defined by a wide variety of properties, such as charge, oxidation
state, structure and degree of complexation.176 Safety can be significantly affected by issues such as
whether radionuclides exist as particles (which may be more easily trapped in the bedrock or clay) or
colloids (which may be much more mobile, see Section 4.3.2). There is particular concern that
actinides, such as plutonium, might be transported long distances on colloids.
Estimation of the transport of radionuclides from a repository requires careful prediction of the
chemical and physical interactions of the radioactive waste with the bentonite buffers and
surrounding rock over extremely long periods of time. The complex mechanisms involved include
advective-diffusive transport of radionuclides in groundwater (including advection, diffusion, and
osmotic and ion restriction effects) and geochemical reactions (complexation, exchange,
precipitation, adsorption and desorption) under different temperatures and pressures. Preliminary
safety assessments have assumed that the chemical retardation of radionuclides in the buffer can be
calculated using a constant retardation factor, Kd. However, more sophisticated computer modelling
of the interactions between the different chemical species and the buffer suggest that using the Kd
approach does not provide a good approximation of contaminant transport and can result in
significant errors.177 In particular, temperature has a great impact on the expected concentrations of
contaminants in groundwater. Coupled thermo-hydro-mechanical-chemical processes will occur,
178
which require complex modelling. The results show that there are still significant shortcomings to
geochemical modelling and its applicability to real-world repository conditions.
The geochemical suitability of a repository site is determined by the composition of the host rock and
groundwater, which influence radionuclide solubility, chemical buffer capacity and radionuclide
retention. However, selection of suitable conditions is generally not straightforward because of the
multitude and complexity of the reactions involved.179 The chemical parameters used in reactive
transport models are not known accurately due to the complex and heterogeneous conditions and
there can be multiple alternative conceptual models, none of which explain the data.180

September 2010 31
Hydrogen produced by the corrosion of canisters and overpacks could act as a reducing agent and
change the chemical conditions in a repository. In particular, the reduction of aqueous or mineral
sulphates and other oxidised species present in the site could change the original geochemical
conditions. Experiments suggest that reaction rates are highly dependent upon temperature but can
181
probably be ignored in nuclear waste performance assessment. However, further investigations are
needed.
4.3.2. Colloids and complexation

A colloidal system is a type of mixture in which one substance (the colloid) is dispersed evenly
throughout another. Milk is an example of a colloidal system, consisting of globules of fat dispersed in
a water-based liquid. Colloid particles have diameters ranging from 1nm to 1µm and have a high
182
surface area. Many radionuclides easily sorb onto colloids suspended in water and this can make
them highly mobile and more easily transported through rock. Computer models that do not account
for transport by colloids can therefore significantly underestimate the rate of transport of
183
radionuclides in groundwater.
Migration on colloids is of particular concern in the case of actinides, such as plutonium, which can
be transported large distances in groundwater as colloids, and as a result could potentially be
184
washed out of the bentonite buffer of a repository, rather than being retained there. There are still
significant gaps in the understanding of the transport of actinides bound to minerals and colloids.
However, experiments suggest that actinide speciation may be dominated by colloid forms.185
Humic matter is decayed organic matter, which is an important constituent of soil. Clay is an
186
important source of humic colloids, which can have significant effects on radionuclide migration.
The bentonite backfill of a repository could generate colloids, which could adsorb or incorporate
radionuclides and transport them over long distances, or retain them by interaction with mineral
187,188,189
surfaces or by agglomeration (gathering together as a mass). Bentonite colloids can diffuse
190
within granite.
Both solid particles and colloids could be detached from bentonite at the bentonite/granite interface in
a repository and mobilised by the water flow. It has been shown that these colloids are very stable in
low saline and alkaline waters, and could facilitate radionuclide transport in the fracture network of
the excavation disturbed zone (EDZ) in the granite around a repository.191
Naturally occurring rare earth elements (REEs) can be used as chemical analogues for studying the
behaviour of actinides. Preliminary studies at the Swedish Forsmark site suggest a strong
association of REEs with colloids in the groundwater in the overlying aquifer but limited mixing and
192
no evidence of transport from the bedrock groundwaters to the aquifer.
The presence of oxidants can also enhance actinide transport significantly, due to the formation of
complex species, which may increase solubility by orders of magnitude and potentially enhance
mobility.193
Cementitious materials are commonly used to stabilise some radioactive wastes, such as long-lived
intermediate-level wastes, which may be co-disposed with high-level wastes in some countries (such
as the UK). In such wastes, cellulosic materials present in the wastes (tissues, cotton or paper) can
exacerbate the above difficulties by forming organic compounds, which may then form complexes
with actinides.194
4.3.3. The role of microbes

Microbiological processes must be taken into account when modelling groundwater
hydrogeochemistry: they are expected to be involved in many reactions which would not occur in a
lifeless underground environment. Experiments in the Äspö Hard Rock Laboratory in Sweden
confirmed the presence of SRB, which produce sulphide corrosive to copper, and autotrophic
acetogens, which produce acetate from hydrogen and carbon dioxide. The analyses also showed
that different rock fractures can have very different hydrogeochemical characteristics and

32 September 2010
microbiological profiles.195 Measurements of the redox state (Eh) and pH at Forsmark and other sites
in Sweden suggest that the waters are buffered by sulphate reduction, consistent with the presence
196
of SRB. The presence of bacteria is important because microbes can affect the mobility of
197,198
radionuclides in a number of ways. They can enhance radionuclide migration by sorption, or
reduce it by immobilising radionuclides in biofilms. They can also influence the release of
radionuclides by altering bulk water chemistry (especially pH and redox), by producing organic
complexing ligands, or by direct accumulation onto or into cells. These complex biological effects on
radionuclide transport are poorly understood but must be considered in a repository safety case.
4.3.4. Release of radioactive gas

The principal source of gas in repository designs that use steel waste containers is expected to be
hydrogen produced by the corrosion of the steel (see Section 4.1.4). The concerns relate to any
damage to containment that might be caused by pressure build-up (see Section 4.2.5) and to the
potential role of the gas in pushing radioactively contaminated water upwards out of the repository.
However, carbon dioxide and methane are other gases that might be produced in a repository. These
gases are likely to contain radioactive carbon-14 and may pose a radiological hazard in themselves
as they leak from the repository.
Carbon-14 has a high production rate in nuclear reactors and is released to the environment in
199
discharges as well as through the disposal of radioactive waste. It has a long half-life (5,730 years)
and high mobility in the environment. The majority of carbon-14 produced in reactors is either trapped
in the spent nuclear fuel, structural materials or graphite moderator, or else produced in the reactor
coolant. A large inventory of carbon-14 produced in nuclear power plants is captured in ion-exchange
resins, which are not heat-generating and hence not classified as high-level wastes. However,
carbon-14 is also contained in spent nuclear fuel, and in some countries long-lived non-heat-
generating wastes may also be co-disposed with high-level wastes in a deep repository.
In the case of a repository for low-level radioactive waste, carbon-14 is the only radionuclide that is
expected to contribute significantly to radiation exposure via the gas pathway, as all other gaseous
radionuclides can be neglected due to their short half-lives, low inventories or low radiological
200
relevance. For example, the Asse salt mine in Germany showed a continual release of carbon-14
during its operational phases as a result of mine ventilation, providing evidence of ongoing reactions
in the waste.201 In many low-level waste facilities, the carbon-14 inventory is the limiting factor in
meeting regulatory requirements. Carbon-14 can be released in groundwater or as carbon dioxide or
methane gas. It is taken up by food crops and vegetables through photosynthesis and by root uptake
from soils, and can then be ingested by humans. For the proposed US deep repository at Yucca
Mountain, the collective dose due to carbon-14 was predicted to exceed the Environmental
Protection Agency’s limit, although the dose per person was low.202
4.3.5. Summary of solubility, sorption and transport of radionuclides

Poorly understood chemical effects, such as the formation of colloids and the role of microbes, could
speed up the transport of some of the more radiotoxic elements such as plutonium. Build-up of gas
pressure in a repository could damage the barriers and force fast routes for radionuclide escape
through crystalline rock fractures or clay rock pores. Radioactive carbon dioxide and methane could
also be released.
4.4. Bedrock properties and hydrogeology

4.4.1. Groundwater flow in the bedrock and fractures
Crystalline rocks contain fractures and faults, which are of critical importance in determining the flow
of radionuclides out of a repository. In contrast, for clay rocks, used in the French concept, a key

September 2010 33
assumption of the safety case is that transport would be by slow diffusion through the clay, rather
203
than through cracks and fissures, which are assumed to be self-healing.
Groundwater flow through crystalline rock takes place mainly through fractures, as the rock itself has
very low permeability. However, flow through both fractures and porous rock needs to be considered
in a safety assessment. This poses particular problems because of the very large degree of
structural variation (known as heterogeneity) in the fracture systems, which means that the
permeability of each piece of rock is different, and varies in different directions.204 The hydraulic
conductivity can vary by one or two orders of magnitude at different points, leading to very different
thermo-hydro-mechanical properties at different points in space.
Despite the progress that has been made in scaling up the measured properties of fractured rock to
try to predict overall flows, the problem is so complex that it has yet to be resolved. Producing
accurate models of fractures in the rock – through which radioactive water and gas can flow – is
difficult because it is hard to extrapolate from measurements on the surface of a block of rock in
order to describe correctly the network of fractures inside it. This means that markedly different
fracture densities, hidden in the rock, could be consistent with the same experimental data.205 An
attempt to characterise a three-dimensional fracture network in a 1m3 block of granite has recently
206
been published: however this is the first data-set of its kind.
At the Forsmark repository site in Sweden, three major sets of deformation zones have been
identified, plus a fourth subvertical zone. Two gently dipping brittle deformation zones seem to play
an important role in determining the properties of the site, such as the distribution of stress, fracturing
207
and transmissivity within fractures. Four main groundwater types are present. The complex
groundwater evolution and patterns are a result of many factors, including present-day topography
and proximity to the Baltic Sea; past changes in hydrogeology related to glaciation/deglaciation, land
uplift and repeated marine/lake water regressions/transgressions; and organic or inorganic alteration
of the groundwater composition caused by microbial processes or rock/water interactions. A major
conclusion from site investigations is that changes from glacial rebound and hence hydrology seem
to have a major influence on groundwater chemistry.208 Currently, the confidence concerning spatial
variation is low due to relatively few observations having been made at depth, and there are
significant uncertainties and discrepancies between models of the site as a result of the different
assumptions made.209 Pore water in the rock has exchanged with water circulating in fracture
networks over extremely long periods of time.210
Mixing models have been used in an attempt to understand how groundwater chemistry has
developed at Forsmark and the alternative Swedish repository site Simpevarp/Laxemar through
mixing of the main groundwater types along with water/rock interactions and biological reactions.211,212
However, the robustness of the model outputs is quite sensitive to the variables included. In addition,
similar mixing proportions and mass transfers can be obtained using different reactions. Further,
when chemical reactions produce an important compositional change the model may not correctly
213
reproduce the mixing proportions.
A coupled model of regional groundwater flow and solute transport, applied to the Simpevarp area,
suggests that the main sensitivities are to the top surface flow boundary condition, the influence of
variations in fracture transmissivity in different orientations (anisotropy), spatial heterogeneity in the
regional deformation zones and the spacing between water-bearing fractures (in terms of its effect on
diffusion through the rock matrix). Again, the best match to the observations may not be unique,
214
introducing additional uncertainty.
The large volume of accessible pores in fractured granitic rock may retard the migration of
215
radionuclides through sorption onto the rock. However, the effects depend on the radionuclide, with
experiments in Sweden suggesting that some actinides are retarded in the rock, while others (e.g.
neptunium) may break through with hardly any retardation.216
Data from the Callovo-Oxfordian clay formation at Bure in the eastern Paris basin – the proposed
French repository zone – suggests that groundwater residence times may be very long, although
significant uncertainties remain due to the complexity of the hydrogeological system.217 The
conductive layers in the clay are heterogeneous and there are several such layers identified as

34 September 2010
218
‘porous zones’. There is also an overpressure – a pressure difference compared to the surrounding
rock – of 20–60m within the Callovo-Oxfordian argillite, which has not yet been explained. The
current preferred hypothesis is that this is due to chemical processes (chemical osmosis in which the
219,220
rock behaves as a semi-permeable membrane). Osmotic flow of water has been shown to occur
221
in samples of Opalinus Clay from Switzerland.
4.4.2. Excavation damage

Excavation causes significant stresses in rock and can change the apertures of fractures, which are
important for determining the future groundwater flow through the wastes in a repository and the
surrounding rock.222 Reduction of pore pressure will also occur during excavation as water is taken
out of the system and gases that were under pressure in the water are released. These processes
can influence fracture size and permeability, making it harder to predict water and gas flows after
closure. After closure, it is not expected that the system will return to pre-excavation conditions,
because of mechanical hysteresis (the effects of past stresses retained in the system).
Excavation damage depends on local geological conditions and the excavation method: for example,
it is greater in the case of drill and blast excavation than with mechanical excavation. The EDZ
consists of a failed zone, in which blocks or slabs may detach completely from the surrounding rock;
a damaged zone containing micro-cracks and fractures; and a larger disturbed zone where rock
stress and water pressures may be altered. If high groundwater flow occurs in the EDZ, concerns
include the possibilities that harmful chemical species may be transported from the surface to the
engineered barriers, diffusion of radionuclides from the wastes into groundwater will be increased
223
and fast routes for release of radionuclides could be created.
When the stresses on the boundary of an underground excavation reach the rock mass strength,
failure occurs. In good-quality hard rock, the failure process involves splitting and cracking, known as
spalling. Calculations in Sweden suggest that the probability of spalling is low down to a depth of
about 550m but that the probability increases below this.224 Explosive spalling (rock bursts) can occur
in hard, brittle rock at these depths.
At depth, it is likely that the excavations will induce stress concentrations above the rock mass
strength. In addition, the heating from the spent nuclear fuel in a repository will increase stresses due
to thermal expansion of the rock. These stresses could affect the stability of the rock mass pillars that
225
surround the canisters and must be taken into account in the design.
Repository construction will require the excavation of many underground openings. In the Swedish
concept these range in size from the 1.8m diameter emplacement holes for the spent fuel, of which
about 4,500 are needed, to an 8m wide x 15m high cavern required for the underground operations
needed to transship spent fuel to different locations in the repository. The excavation-induced
stresses form an EDZ in which hydromechanical and geochemical modifications induce significant
changes in flow and transport properties.226 Strength degradation of the rock may occur over time due
to micro-cracking or micro-fracturing.227
In clay rocks such as those in France, methods are being developed to limit the flow of groundwater
228
through the EDZ by creating radial slots filled with bentonite to interrupt the flow. Clay-based seals
229,230,231
may be key components in repository designs.
In clay rocks studied in France and Belgium, an unpredicted hydraulic perturbation was found at a
large distance (greater than 30m) from excavation in both clays. Herringbone fractures were
observed ahead of the gallery excavation front and boreholes, and eye-shaped fracture patterns
were also observed around boreholes.232
In the Opalinus Clay in Switzerland it has been found that the possibility of temperature-induced
233
deformation of clay rocks due to the emplacement of high-level wastes cannot be neglected. At the
surface, an uplift of up to 1m has been predicted. This is expected to occur smoothly and over a wide
area, so is not considered likely to cause major damage to surface structures. However, below the
surface significant damage could occur to tunnels and to tunnel linings, unless they are sufficiently
strong or flexible.

September 2010 35
4.4.3. Gas flow
It is now recognised that the ability to understand and predict underground gas migration is crucial to
the design and management of nuclear waste repositories. However, computer models of combined
water and gas migration (known as two-phase flow) in an underground nuclear waste repository are
still at an early stage of development.234,235,236,237,238 Considerable complexity exists due to the highly
different porous media that may surround the gas-generating waste packages: concrete buffers or
plugs, bentonite backfill, and damaged or fractured zones in different host rocks. Heat-damaged
(cracked) bentonite backfill or clay rock and excavation-damaged or fractured rock may provide fast
routes for gas escape.
4.4.4. Summary of bedrock properties and hydrogeology

Unidentified fractures and faults, or poor understanding of how water and gas will flow through faults,
could lead to the release of radionuclides in groundwater much faster than expected. Excavation of a
repository could create fast routes for radionuclide escape through the part of the rock damaged by
the excavation.
4.5. Human intrusion and human error

239
Other scenarios which should be considered include human intrusion. Spaces deep below ground
may be subject to hydrocarbon or mineral extraction and increasingly used for geothermal energy
production or for storage: for example, storage of gas for energy in salt caverns, or potentially
240
storage of hydrogen or of CO2 as part of planned carbon capture and storage systems. This raises
the possibility that future generations seeking to access such spaces may inadvertently drill into a
repository and be exposed to potentially high levels of radiation. Repository sites are supposed to be
chosen to minimise the risk of human intrusion by avoiding sites likely to be subject to the extraction
of raw materials (minerals, coal, oil, gas) or drinking water or used for geothermal energy
241
production. However, in practice it may be impossible to anticipate how future generations will wish
to use underground space and resources. If human intrusion takes place in the form of underground
drilling, radioactive wastes could be rapidly released. Solid material, which might be highly
radioactive, could be rapidly ejected from a repository into a borehole during an exploratory drilling
operation if the gas pressure in the repository exceeded the pressure of the column of drilling mud.242
Deliberate intrusion is also possible in that the contents of repositories could be attractive to some –
some of the wastes would be suitable for the manufacture of nuclear weapons and dirty bombs for
thousands of years and the sites will also contain very substantial amounts of precious raw materials.
Human error during the process of disposal is one of the hardest scenarios to identify and evaluate.
Issues include the use of damaged canisters or overpacks and the disposal of poorly catalogued
materials. If fresh, rather than irradiated, nuclear fuel were buried, it could undergo a nuclear chain
reaction (criticality) while underground, potentially causing significant damage to the engineered
barriers and the surrounding rock.243
4.6. Ice ages and glaciation

One of the greatest long-term threats to the integrity of deep repositories is likely to be the effects of
future glaciation. Despite global warming, the next glaciation is expected to occur at 10,000 to
100,000 years in the future, and glaciation/deglaciation is likely to cause the most significant
244
perturbation to a repository in this timeframe. There have been at least five ice ages in earth’s
history; several factors are thought to be important in causing them, including changes in the earth’s
orbit around the sun and variations in the sun’s output. The last glaciation ended more than 8,000
years ago but its effects on geology and groundwaters are still visible. Post-glacial rebound – the
slow upward movement of rocks which occurs after the weight of the ice has been removed – is still
occurring in regions that were under ice sheets, such as northern Europe and Canada.
Repository sites in Europe and Canada are likely to be affected by future glaciations because future
ice sheets are likely to extend over similar regions to those in the past.245 Direct erosion of glacial

36 September 2010
troughs and fjords by ice in Europe was confined to Scandinavia, Scotland and the Alps, but more
minor incisions and meltwater channels extended over a much larger area. Major fault displacements
(scarps) occurred in northern Sweden and smaller ones in Finland and Canada. Sites near the
margins of future ice sheets will be subject to repeated glacial advances and retreats and will thus
undergo repeated rock stresses and hydrological changes. The greatest problems are likely in
lowland regions exposed by the rapid retreat of thick ice fronts, where large lakes on or under thick
warm-based ice are dammed by more distant cold-based ice. Groundwater in fractures dilated
(opened up) by glacial unloading may reach over-pressures capable of hydraulically lifting blocks of
bedrock or eroding more permeable rocks to depths of about 360m. When the load of grounded ice is
lifted, deep accumulations of hydrocarbon gases may be capable of blowing craters or caves in
bedrock. Rapid retreats of future ice sheets may therefore represent the horizon to practical safety
assessments for nuclear waste repositories.
Ice meltwater, which is alkaline, could significantly change the composition of the pore water around
a repository and the chemistry of the bentonite buffer.246 An oxidising environment at depth would
increase the solubility and mobility of many radionuclides and the corrosion of the canisters. Melting
of glaciers is likely to be accompanied by oxidation and the formation of iron oxides, although studies
in Sweden suggest that oxygenated waters do not readily penetrate beyond a depth of 100m, so a
247
deep repository may be well-protected. However, modelling suggests that oxygen could reach long
distances downwards during the lifetime of a repository and penetration will depend on hydraulic
properties that may vary significantly with location, with, for example, oxidising conditions occurring
after a relatively short time if a fracture connects the repository with a highly conductive fracture
zone.248 The presumed depth of dissolved oxygen migration is greatly influenced by the assumptions
249
that are made in the conceptual models.
Research using samples of brines occurring in crystalline rocks in Canada, Finland and Sweden
suggests that these waters have been concentrated from seawater, by freezing during glacial times.250
The researchers calculate that these brines were formed relatively recently (within a few hundred
thousand years during the Pleistocene period, which began more than 2 million years ago and ended
around 10,000 years ago) and that the consequent dynamic behaviour of the cryogenic fluids is in
disaccord with the established consensus that the hydrological system in deep crystalline basement
rocks is stagnant. They state that this finding should raise concern about the planning and
construction of high-level nuclear waste repositories in such rocks.
Measurements of minerals deposited in fractures at Forsmark show that different generations of
fracture minerals are common, which implies that the fractures have been conductive several times
and probably for long periods. Waters of quite different chemistry have been present at different times
over the past million years as a result of repeated glaciation/deglaciation and
transgression/regression of the Baltic Sea251. There are also many older fracture-filling events
252,253,254
involving the migration of fluids many millions of years ago.
A study of the release of uranium from the Palmotto natural uranium analogue site in Finland
suggests that release occurred in two or three violent episodes in the last 300,000 years, probably
due to repeated inflows of oxic glacial meltwater.255 At the UK Sellafield site, borehole measurements
suggest that cold climate recharge occurred at depths of about 700m, probably during the
Pleistocene glacial periods between 2 million and 10,000 years ago.256
Modelling of the effects of a future glaciation on a hypothetical repository in the Canadian Shield,
based on the last glacial cycle between about 60,000 and 11,000 years ago, suggests that under
extreme conditions permafrost is able to develop down to the assumed 500m repository depth or
lower. During ice sheet advance, there is a rapid rise in hydraulic head (pressure due to the ice
sheet), high groundwater velocities (two to three orders of magnitude higher than under non-glacial
conditions) and deeper recharge from surface water. During ice sheet retreat, the gradients reverse.
In the fracture zones, the upward hydraulic gradient lasts for about 100 years, whereas in the rock
matrix at depth it can last for tens of thousands of years.257 The effects of temperature, salinity, stress-
dependent permeability, permafrost and large-scale isostasy (i.e. the effects of the weight of the ice
on the rock) were omitted from the coupled hydro-mechanical computer model of water flow in the
rock underneath the ice, although the formation of permafrost may have significant effects on
258
groundwater flow and chemistry. The modelled head distribution is 3D, reflecting the 3D nature of

September 2010 37
259
the geometry of the fracture zones in the rock and the subglacial drainage channels. The details of
the fracture network modelled significantly affect the response.
A model of the effects of glacial cycles on the Bure potential repository site in France has identified a
memory effect of the last glaciation at depth, where as much as 80% of the last glacial maximum
head disturbance may remain.260
The long-term effects of glaciation on repository safety could be very serious, potentially involving a
large release of radionuclides due to glacial flushing from a damaged repository zone. Future
glaciations could cause faulting of the rock, rupture of containers and penetration of surface and/or
saline waters to the repository depth, flushing out radionuclides as the ice melts. Future glaciations
therefore place a serious limit on the predictability of containment of the buried wastes.
4.7. Earthquakes
Inactive faults may be reactivated during the lifetime of a repository and earthquakes could severely
damage the containment system, including the canisters, backfill and the rock.
Networks of monitoring stations in north-west Europe have identified the positions of seismic events
since the 1970s. In Britain, there are two regional-scale clusters of seismicity, one occupying the
length of onshore western Britain and the southern North Sea, the other in the northern North Sea.
However, this seismicity data only represents a few decades of observations and it could be argued
that this length of historical record is not very relevant to earthquake hazard assessment over periods
of tens of thousands of years. Seismic reflection data indicate that the fault density is as great in the
areas of the UK that have been seismically quiet in the historical period as it is anywhere else; given
the difficulty in declaring a fault extinct, such faults could become seismic hazards during the lifetime
261
of a repository.
The Pärvie Fault system in northern Sweden contains faults that have been reactivated since the
Precambrian and which are strong candidates for future movement under suitable stress
conditions.262 In Finland and Sweden, changes in the mass of glacial ice sheets associated with
periodic advances and retreats of ice are associated with very strong earthquakes. It is difficult to
predict the extent to which faults may be reactivated by glaciations.
4.8. Transport of radionuclides in the biosphere

Once radionuclides reach the biosphere, they may expose humans to radiation in a variety of ways.
As part of the safety assessment of a proposed repository, computer models are used to calculate
expected doses to humans via pathways such as ingestion of radionuclides in drinking water and
263
food, inhalation of radionuclides, and external radiation from radionuclides in soils.
Computer models of the behaviour of relatively well-known radionuclides in scenarios such as a
nuclear accident can give reasonable predictions. For example, a comparison of nine computer
models of ecological transfer and thyroid doses resulting from the release of iodine-131 following the
Chernobyl nuclear accident found agreement within a factor of ten with dose measurements.264
However, different radionuclides move in different ways in the near-surface environment, including in
265
soils, lakes and streams. There may be multiple migration mechanisms involved, including
266
transport by air, water, particulate matter and biota, which further complicate dose estimates.
Estimates of the effects of radionuclide exposure on health may also be revised in future as scientific
267
understanding improves.
The speciation of radionuclides is of great importance for biological uptake, accumulation and
biomagnification.268 Radionuclide transfer from soils to food crops can vary considerably with the
radionuclides, plant species, soil types and times of deposition, and there is considerable uncertainty
269
regarding these transfer factors. Many data gaps also remain in factors governing the transfer of
radionuclides in animal feedstuffs to domestic farm animals, which will contaminate the human food
chain via meat and milk.270 Repositories located near to the coast are expected to discharge some
radionuclides into the marine environment and here too there are uncertainties regarding the
bioaccumulation of radionuclides in different species of fish and shellfish, and particularly in the rates

38 September 2010
of sorption and re-release (desorption) of radionuclides into and from seabed sediments over long
271
timescales.
Until recently, it was assumed that plants did not play an important role in the transport of actinides
such as plutonium in the biosphere. However, studies of the US plutonium-contaminated site at
Savannah River have shown that a large proportion of the buried plutonium has unexpectedly
migrated upward. Simulations indicate that because plants create a large water flux, small
concentrations taken up in plants over long periods may result in a measurable concentration of
272
plutonium on the ground surface. This finding will not be relevant to repository safety if actinides are
contained by sorption in the bentonite backfill deep in the repository. However, the concentration of
plutonium by plants could be an issue of concern if it is transported to an aquifer faster than
expected, perhaps in the form of colloids (see Section 4.3.2).
Plutonium has also been detected in groundwater in the prevailing flow direction in a borehole close
to the vault at the Maišiagala shallow radioactive waste repository in Lithuania. Investigation of
possible colloid-mediated transport is planned. The presence of tritium and carbon-14 in groundwater
at the Maišiagala site (which operated from 1963 to 1989) also suggests possible uptake of these
273
radionuclides in plants, with measurements confirming the transfer of tritium to plants.
Other mechanisms of radionuclide transport and accumulation, as well as impacts, may be missed
because the current approach to radiological protection is based on simplification of systems, rather
274
than acknowledging and addressing complexity. A more ecosystem-focused approach would
recognise multiple feedbacks (such as the ways that organisms can affect environmental
concentrations of radionuclides, as well as vice versa), the limitations of extrapolations and the
275
potential importance of indirect and ecosystem effects over long timescales. One example of an
area that is only just beginning to be studied is the accumulation of radionuclides in invertebrates,
including beetles, ants, spiders and millipedes, which are a major dietary component of many animals
276
and therefore one potential route into the human food chain.
Climate change – including both global warming and future glaciation – will change ecosystems
significantly, including drastic changes from aquatic to terrestrial systems and vice versa as sea
levels rise or fall at a particular location. This prospect poses additional challenges for radiological
protection.277 Currently, different climate states are considered in safety assessments, but not the
transitions between them: this means that some scenarios that might result in higher releases – such
as the accumulation and then release of radionuclides below an ice shield during a glaciation event –
are not included in the models.278 Processes at the biosphere/geosphere transition zone (such as
groundwater recharge rates) are also neglected, although they may be essential for modelling
radionuclide mobility during climate transition phases.
A typical scenario for future exposures presumes the existence of a group of people living above a
repository and deriving all its water from a well in the aquifer above the waste. The water is used for
drinking by humans and animals, exposing people directly via the water and via meat, milk and eggs
from the livestock; and also for irrigation, exposing people via soil contamination, plant uptake, and
ultimate ingestion of soil and plants, as well as via external exposure and inhalation of suspended
soil.279 There are significant social uncertainties regarding future human behaviour, as well as
uncertainties in the physical, chemical and biological behaviour of each radionuclide. Further,
because radionuclides are assumed to be diluted in the well, the above scenario may not always be
the highest exposure route for future generations, compared with, for example, consumption of fish or
280
shellfish in which radionuclides have bioaccumulated.

September 2010 39
5. Overarching unresolved issues
5.1. Safety assessment: the evidence base, the methodology and its limitations
The literature review set out above suggests that significant releases of radioactivity from a deep
underground repository could occur in a number of ways:
l The effects of intense heat generated by radioactive decay, and of chemical and physical
disturbance due to corrosion, gas generation and biomineralisation, could impair the ability of
backfill material to trap some radionuclides.
l Build-up of gas pressure in the repository, as a result of the corrosion of metals and/or the
degradation of organic material, could damage the barriers and force fast routes for
radionuclide escape through crystalline rock fractures or clay rock pores.
l Poorly understood chemical effects, such as the formation of colloids, could speed up the
transport of some of the more radiotoxic elements such as plutonium.
l Unidentified fractures and faults, or poor understanding of how water and gas will flow through
fractures and faults, could lead to the release of radionuclides in groundwater much faster
than expected.
l Excavation of the repository will damage adjacent zones of rock and could thereby create fast
routes for radionuclide escape.
l Future generations, seeking underground resources or storage facilities, might accidentally
dig a shaft into the rock around the repository or a well into contaminated groundwater above
it.
l Future glaciations could cause faulting of the rock, rupture of containers and penetration of
surface waters or permafrost to the repository depth, leading to failure of the barriers and
faster dissolution of the waste.
Although computer models of some of these processes have undoubtedly become more
sophisticated, fundamental difficulties remain in predicting the relevant chemical and geochemical
reactions and complex coupled processes (including the effects of heat, mechanical deformation,
microbes and coupled gas and water flow through fractured crystalline rocks or clay) over the long
timescales necessary.
To date, preliminary safety assessments have been produced for the selected sites in Forsmark,
281 282 283
Sweden and Olkiluoto, Finland and the selected region of Bure, France. All these assessments
have been produced by the nuclear waste management organisations SKB (Sweden), Posiva
(Finland) and Andra (France) themselves. Safety assessments have also been produced in the past
for the Yucca Mountain site (now abandoned) and for the failed plan to bury long-lived radioactive
wastes near Sellafield in the UK.284
According to the Finnish nuclear waste disposal company, Posiva, the following issues are still
285
pending final resolution and will be addressed in future updates:
l the initial state of the site (e.g., in situ stresses, the fracture network, hydrogeochemical
conditions at repository depth)
l the impact of the EDZ and thermal spalling on the hydraulic evolution
l the evolution of buffer/backfill saturation (e.g. time to reach full swelling pressure) and its
consequences for the performance of the engineered barrier system

40 September 2010
l flow paths to and from the repository (e.g. groundwater flows at canister scale, release paths
for radionuclides)
l reaction rates and (experimental) evidence of the sequence of hydrogeochemical reactions in
the near field, especially with respect to the reactions leading to the production of sulphide
l the impact on the engineered barrier system of cementitious materials and other stray
materials used in repository construction
l the long-term performance of repository closing and sealing materials and the consequences
for safety
l the impact of external conditions related to glaciations – e.g. taliks (unfrozen layers of ground
in regions of permafrost) and glacial meltwater intrusion – on the long-term performance of
the engineered barrier system.
However, there remain fundamental difficulties in resolving these issues, as discussed below.
5.1.1. Unknowns, uncertainties and model validation

A landmark paper published in 1994 argued that verification and validation of numerical models of
natural systems is impossible.286 This is because natural systems are never closed and because
model results are always non-unique. Models can be confirmed by the demonstration of agreement
between observation and prediction, but confirmation is inherently partial. Computer models can only
be evaluated in relative terms, and their predictive value is always open to question.
The objective of site investigations for a nuclear waste repository is not primarily to produce a
geoscientifically ‘true’ model, but rather to provide a basis for good decisions. Results are subject to
uncertainty not only due to inherent variability but also due to ‘lack of knowledge’ (epistemic)
uncertainties, including systematic bias, which can have a large influence on the results. It is usually
assumed that the underlying physics or chemistry of the problem being modelled is fairly well
understood and that there is no fundamental misunderstanding of the problem prior to investigation.
However, there are situations where an investigation may provide surprising information, calling for a
287
revised conceptual model of the problem. Historic examples include collapses in fish stocks, the
288
effects of CFCs on the ozone layer, and the harm to health caused by X-rays and asbestos.
One problem is that many different models may be consistent with the available data.289
Therefore even perfectly calibrated models (e.g. those that fit the data at a particular site) may have
limited or no predictive value (i.e. they may not adequately represent the necessary processes as
290
conditions change with time). Similarly, models that work well in the laboratory may not apply to
real-world conditions. For example, the advection-diffusion equation is used to predict the transport
of solutes in soils. However, it neglects the possibility of preferential fast transport routes, particularly
on colloids, and therefore failed to predict the unexpected pollution of steams and groundwaters with
pesticides and other contaminants.291
Another problem is the difficulty in finding a parameter set that adequately represents a given
location, because places are unique in their characteristics and boundary conditions and their
uniqueness is inevitably to some extent unknowable.292 This means that a model that has been
refined to be ‘fit for purpose’ at one location will not necessarily work at another, or in different future
circumstances, if the parameters used to define the new site or circumstances are inadequate to
represent important processes.
Theoretically, it should be possible to take a pragmatic approach which would allow researchers to
consider all the possible models that might fit the data and, by hypothesis testing using experimental
data, rule out those models that breach safety requirements.293 However, most safety assessment
programmes remain wedded to the idea that there is a single ‘best fit’ model, rather than focusing on
exploring possible alternative models of the site, some of which may show the proposed repository to
breach safety requirements. Further, it is by no means clear that sufficient data can be collected, or
sufficiently safe sites exist, to rule out scenarios which involve significant radiological releases.

September 2010 41
5.1.2. Potential for bias in the assessment process
Scientific bias has been well studied in the medical research literature, where several types of
interpretative bias (bias in the analysis of data, rather than in the measurements themselves) have
been identified:294
l confirmation bias – evaluating evidence that supports the scientist’s preconceptions
differently from evidence that challenges these convictions
l rescue bias – discounting data by finding selective faults in the experiment in order to
‘rescue’ the original hypothesis
l mechanism bias – being less sceptical when underlying science furnishes credibility for the
data, meaning that the interpretation of results is in line with prior expectations
l “time will tell” bias – the phenomenon whereby different scientists need different amounts of
confirmatory evidence, because deciding when evidence is sufficient to make a decision is
inevitably subjective
l orientation bias – the possibility that the hypothesis itself introduces prejudices and errors
and becomes a determinate of experimental outcomes.
In the field of deep disposal, the likelihood of interpretative bias is high and the potential safety
implications considerable, because the wastes involved remain highly dangerous for thousands to
millions of years and there is no mechanism to validate computer model predictions over the long
timescales involved. In systems whose properties are spatially and temporally heterogeneous
(variable) at different scales the concept of the observer as an impartial, totally unbiased bystander
becomes meaningless.295 Models of environmental systems, including radioactive waste disposal,
involve numerous subjective choices about system structure, boundary conditions, feasible values
for parameters, characterisation of input data, scenarios for future predictions and how the
performance of the model should be evaluated.296 Environmental models are therefore
mathematically ill-posed or ill-conditioned, meaning that the information content available to define a
297
modelling problem does not allow a single mathematical solution.
Failure to recognise this can easily lead to overconfidence in a particular computer model or the
assumptions that underpin it. It is clear from historical and contemporary examples drawn from many
fields – a recent example being the credit crunch of 2007 – that highly expert regulators and private
risk modellers sometimes exhibit ‘herd behaviour’ and may fail to anticipate rare and unexpected
events. Such dangers are greatest when the discussion of the issues and computer model-building
are highly complex and are comprehended only by a highly expert group, because they are then less
likely to be open to public scrutiny or challenge by outsiders.298
Numerous articles in the medical literature have also found that bias is strongly influenced by
299,300,301,302,303,304
commercial interests. This suggests that the selection of a particular computer model
and set of parameters may be not only subjective, but also easily biased towards giving the preferred
outcomes.
Availability of alternative expertise and funding can therefore strongly influence whether there are
sufficient critical perspectives to identify problems with the safety case for a radioactive waste
repository.
For example, at the UK Nirex planning inquiry, the objecting groups had a total budget one hundredth
that of Nirex but nevertheless succeeded in demonstrating significant problems with the safety case
by involving sufficient alternative expertise. Nirex produced seven expert witnesses to discuss the
technical, geoscience and engineering issues: all except one were directly employed by Nirex.305 For
the objectors, Cumbria County Council produced five experts (one employed by it), focusing on site
selection, hydrogeology and overall risk. Greenpeace presented five experts (one employed by it) to
discuss site selection, geology, hydrogeology, flow modelling, geochemistry, and comparable
investigations worldwide. Friends of the Earth fielded nine experts (two employed by it) to tackle
government policy, geology, site 3-D structure, hydrogeology, fluid flow in fractures, engineering and
geochemistry. In one example of the expert evidence presented, alternative groundwater flow
modelling by researchers at the University of Glasgow, funded by the Greenpeace Environmental

42 September 2010
Trust, suggested that much faster groundwater return flow times than those calculated by Nirex were
306
more consistent with its borehole measurements, implying that Nirex’s risk calculations might be
two orders of magnitude in error.307
Similarly, much of the work highlighting concerns about the potential for copper to corrode in water
(see Section 4.1.2) has been unfunded. The official research programme did not identify this
problem.
These examples suggest that other problems may remain unidentified due to lack of sufficient
independent scrutiny.
Bias can be exacerbated by claims that deep disposal must be workable because ‘road maps’
towards its implementation exist in a number of countries, significant amounts of research have been
done, and other alternatives have been discarded as technically or economically unfeasible or
unsafe.308,309
In Finland, a Posiva researcher speaking anonymously to the Finnish Broadcasting Company in May
2010 expressed concerns about pressure on scientists to meet the schedule for approval of the
Olkiluoto repository despite doubts about the reliability of the copper canisters, bentonite backfill and
tunnel backfill. The researcher reportedly said: “The results of research are decided beforehand.
Then we find data that gives the desired result. If there is information that does not back up the
result, it is ignored”..310
It seems likely therefore that there could exist other serious problems with deep repository proposals,
which have not been identified due to lack of resources and funds for independent scrutiny of data
and assumptions. In each country with a deep disposal programme, regulators are responsible for
reviewing safety cases and ultimately for licensing facilities.311 Although this can include some
independent research and development to support decision-making, regulators are in practice largely
dependent on the data collection, analysis and computer modelling produced by the nuclear waste
disposal companies.
The majority of the funding for research, development and demonstration (RD&D) in waste
management comes from the nuclear industry and follows the research agenda set by the industry’s
312
implementing organisations. Reliance on industry-funded research, although consistent with the
principle that the polluter pays, is likely to introduce interpretative bias in repository safety
assessments. On the other hand, significant sums of public money invested via Euratom are not
being used to fund independent scrutiny. It is of particular concern that Europe’s IGD-TP states that it
is open only to stakeholders “endorsing the vision and willing to contribute positively and
constructively to the objectives and goals of the platform” – in other words, critics of deep disposal
are supposed to be excluded from the research programme and hence from Euratom funding.313
Greenpeace has now joined the IGD-TP but only on condition that it is not required to subscribe to
the vision. Members of the Executive Group consist of organisations either responsible for
implementing a waste management programme or formally responsible for the RD&D programme
needed for implementation.
It is difficult to see how adequate independent scrutiny of data and assumptions can take place in
such circumstances.
5.2. Site selection, public opinion and radioactive waste inventories

Sweden has involved local communities in the decision-making process and given them a veto at
each stage of the site selection process for a deep repository. Following the example set by Sweden
and the past failures of site selection processes in many countries, there has been a shift in most
countries since the 1980s away from finding the best geological site for disposal towards finding a
site that is considered good enough and where repository construction is considered politically as
well as technically achievable. The site selection process then takes more account of other factors,
particularly acceptability to the local population and proximity to existing nuclear facilities.314
The UK and Canada have been particularly active in attempting to be seen to follow the Swedish
approach by introducing new public participation and consultation programmes for nuclear waste
disposal decisions.315

September 2010 43
The Canadian nuclear waste management programme settled on deep disposal as a solution by the
mid-1970s, initially projecting site selection by the mid-1980s, construction of a repository by the late
1980s, and an operating repository by 2000. Intense public opposition thwarted this programme,
which failed to gain popular acceptance at a public inquiry, but a new process of site selection is
currently under way.316 It remains to be seen whether technical problems and scientific uncertainties
are truly open to public scrutiny, or whether official claims that deep disposal has been “found to be
safe from a technical perspective” will remain unchallenged.
In the UK, proximity to existing nuclear facilities previously led to a focus of investigations on the
suitability of Sellafield as a site for the planned Nirex intermediate-level waste repository, which was
rejected in 1997. The new approach therefore differs little on one level in that the same area has now
been shortlisted again; however, this time people living near the final site are expected to be offered
compensation. On the other hand, planning law has been changed so that the scientific evidence
cannot be cross-examined (see Box 6).
Site selection processes based on ‘volunteerism’ typically now involve some form of financial
compensation for the local population and perhaps other benefits, such as employment and new
roads or other infrastructure. For example, in Slovenia two communities close to the country’s only
nuclear power plant competed for the financial compensation available for hosting a repository for
low- and intermediate-level waste.317
However, a voluntarist approach to site selection for a deep geological repository presumes that a
number of sites that are both geologically suitable and publicly acceptable exist, and that safety will
not be compromised by offering financial incentives to poor or marginalised communities. In practice,
offering financial compensation risks undermining the requirement to ‘optimise’ radiological protection
(i.e. to use the best available techniques to minimise radiation exposures in the future). Further, as
the European Commission’s JRC acknowledges, a suitable site might simply not exist in a given
318
country seeking to implement the deep disposal option.
A study of the siting of a low-level waste repository in South Korea identified four factors that
influenced local acceptance: perceived economic benefit, risk perception (which has strong negative
319
effects), trust and perceived competition for the facility. In Sweden, one study has suggested that
people in the two municipalities shortlisted for a spent nuclear fuel repository have less precautionary
attitudes to risk than the general population.320 There is thus a danger that concerns about repository
safety and impacts on future generations may be sidelined in communities which volunteer to host a
repository, especially if they are economically dependent on the compensation, infrastructure or jobs
offered to them.
A recent survey of public attitudes in Finland provides strong evidence that residents in the
municipality of Eurajoki, where the Olkiluoto disposal site is to be situated, perceive a threat to the
safety, health and well-being of future generations from the planned repository.321 The site was
shortlisted when the use of purely geological criteria had been abandoned, and was inserted onto a
list of 101 potential sites as an ‘exception’, based on the short transport distance that would be
required for the wastes already stored at the nearby nuclear reactors. The survey, based on 606
responses which qualified for analysis, found that 63% expected a positive effect on employment and
economic development in the area, but that the facility was widely expected to have a harmful impact
on rural non-farm livelihoods (fishing, hunting, forest product gathering etc.), the state of the
environment near the facility and the image of the area (to outsiders). Nearly 60% of respondents
agreed with the statement “Nuclear waste poses a continuous threat to the lives of future
generations” and only 23% disagreed with it. A majority felt that the repository posed a threat to the
safety of future generations (55%), the health of future generations (55%) and the well-being of
future generations (52%).
The information provided by the survey is important because this is the first municipality in the world
where the views of local residents have been able to be studied following a site selection decision for
a deep underground repository for spent nuclear fuel. The survey suggests that, far from being
convinced about the long-term safety of the proposed facility, residents have reservations and a high
level of concern about future generations. However, these reservations have not led to the
community vetoing the site, thanks to a package of economic benefits negotiated between the
322
municipality and the nuclear industry in 1999–2000.

44 September 2010
This tension between long-term safety and short-term economic incentives has also been seen in the
UK, where compensation is now being offered to communities that volunteer to host a repository.
Selection of the Sellafield site in 1991 for a repository for long-lived intermediate-level waste involved
a process which gave zero weighting to safety criteria on the grounds that all short-listed sites could
meet regulatory requirements. However, the chosen site met none of the geological criteria or
323
guidelines that had ever been developed to identify appropriate sites. The rejection of planning
permission for a Rock Characterisation Facility (the first phase of the planned repository) at this site
in 1997 was the third time the then UK disposal company Nirex had its plans rejected.324 A key issue
at the inquiry was the site selection process and Nirex’s failure to optimise radiological protection
using best available techniques. The site was chosen for non-scientific reasons, in a decision-making
process which concealed its true geological problems, leading geologists who gave evidence against
the plans to conclude that the planning inspector’s comprehensive dismissal of the site would make it
hard to return to it.325,326 Over a decade later, a new planning system has now been adopted to
327
facilitate the construction of new nuclear reactors and the associated nuclear waste repositories.
New geological criteria which do not exclude the Sellafield area have been developed, despite
continued concerns that the area is geologically unsuitable.328,329 Volunteer communities are being
sought for a repository, to receive high-level as well as intermediate-level wastes from past and
current reprocessing, plus spent nuclear fuel from new nuclear reactors, and three communities near
Sellafield have expressed an interest.330,331 The new planning system thus appears designed to allow
construction of a repository to proceed at or near the previously rejected site. It remains to be seen
whether this process is successful at building public confidence.
In several countries, including Canada, the UK, Sweden and Finland, the difficulties of implementing
deep disposal have been exacerbated by government decisions to build new nuclear reactors,
threatening to create new wastes before a solution has been agreed or implemented for existing
wastes. Rather than reiterating the conclusion of the 1976 Flowers report that new reactors should
not be constructed in the absence of a safe means of containing the wastes, the UK Government has
adopted an active programme of new reactor construction, claiming that there is now a consensus
that deep geological disposal is safe. In a sign of tension, the UK Committee on Radioactive Waste
Management has clearly stated that its conclusions and recommendations regarding deep disposal
are intended to apply only to committed wastes, not to wastes generated by new nuclear power
stations.332 Issues include the ethical concerns associated with producing new wastes before a
solution has been demonstrated, and the increased difficulty of finding a suitable volume of rock.
In Finland, where a new reactor is currently under construction, the nuclear waste company Posiva
has rejected the proposal that it dispose of waste from the new reactor, which is owned and
managed by a different company.333 The construction of new reactors will increase not only the
volume of wastes to be disposed of but also the average level of radioactivity per rod of spent
nuclear fuel, since next-generation reactors are likely to use higher burn-up fuel. This may have
implications for repository safety cases.334
Thus, in addition to the tension between the economic benefits being offered to host communities
and long-term repository safety, there is a tension between endorsement of deep disposal as a
potentially ‘least bad’ option for existing wastes, if the scientific and technical difficulties can be
resolved at some point in the future, and nuclear industry claims that deep repositories provide a
safe solution which will allow the ‘sustainable’ expansion of the industry.
Yet there is little public support for the idea that the problem of high-level nuclear waste has been
dealt with in the sense that it can now be ‘got rid of’ safely. According to a 2008 Eurobarometer
survey, in Greece, Sweden, France, Germany and Finland around 80% of respondents “totally” or
335
“tend to” agree that there is no safe way of getting rid of high-level radioactive waste. Of EU
residents as a whole, 41% totally agreed that there is no safe way of getting rid of such waste, while
under a third (31%) tended to agree. Only 14% disagreed and a similar percentage did not know or
had no opinion on the issue. The idea that there is no safe way of getting rid of high-level waste had
slightly more support in Finland in 2008 than in 2005, while Cypriot, Lithuanian, Hungarian, Latvian
and Dutch respondents seemed to have become more convinced by the opposite statement, i.e. that
there is a safe way of getting rid of it.

September 2010 45
The 2008 Eurobarometer survey also found that public opinion was rather divided across the EU over
deep underground disposal of high-level waste. In Finland, Sweden and Hungary this idea received
more support than anywhere else in the 27-member EU. Majorities in Luxembourg and Belgium did
not agree that deep underground disposal represents the most appropriate solution and the largest
single response in France, Poland, Italy and Latvia was also disagreement. In some countries very
high proportions of citizens answered that they did not know whether deep underground disposal is
the best solution.
The respondents were asked which things would worry them the most if a disposal site for radioactive
waste was built in the area where they live. The main issues of concern were the possible effects on
the environment and health (51%) and the risk of radioactive leaks (30%). Of all those surveyed,
eight out of ten responded that one of these two issues would worry them the most. EU residents
would clearly want to be directly consulted and would like to participate in the decision-making
process, should this hypothetical situation take place – well over half of respondents (56%) indicated
that they would want to be personally involved. Just over one in five (22%) indicated that they would
prefer local non-governmental organisations to participate in the decision-making process, while 15%
felt that they would rather let the responsible authorities decide.
The IGDTP Vision Document states that it is essential to develop dialogue with the general public so
as to share the extensive scientific and engineering work underpinning the conclusions made by the
OECD NEA that geological disposal is technically feasible and “provides a unique level and duration
of protection”. This issue is being dealt with in the Forum on Stakeholder Confidence in the
336
Radioactive Waste Management Committee of the NEA .
This suggests that, rather than genuinely seeking to address scientific and technical concerns, the
nuclear industry and advocates of new nuclear reactors, such as Euratom and the NEA, are actively
engaged in a public relations exercise focused on the claim that no major issues remain to be
resolved. One example of such advocacy is a web-based communication system funded by the
Japan Nuclear Safety Organisation to seek ‘social consensus’ on high-level waste disposal.337
5.3. Costs
The global market for nuclear decommissioning and clean-up is estimated at £300 billion (€360
billion) over the next 30 years.338 The costs of deep geological disposal are significant: for example,
South Korea has estimated the cost of its proposed spent fuel repository as 2.6 billion euros.339
The cost of the copper canisters is one of the key components of the cost of a nuclear waste
repository built according to the Swedish concept. In South Korea, 14,210 canisters will be needed to
dispose of spent fuel consisting of 36,000 tonnes of uranium from the two existing reactor types
(11,375 pressurised water reactor (PWR) canisters and 2,835 CANDU canisters). As part of a cost-
estimation exercise in Korea, the cost of a CANDU canister consisting of a 5cm copper outer shell
with a cast iron insert was calculated at €171,415 and the cost of a PWR copper canister produced
using the cheapest method at €156,776 (2006 prices). In these calculations, the material cost was
about 43% of a canister’s total manufacturing cost (the rest being mainly labour costs), and the
340
manufacturing cost of the canisters represented about 32% of the total disposal costs. South Korea
accordingly plans to use a thinner (1cm rather than 5cm) copper canister to reduce costs;341 however,
this will impact on containment and hence on safety. There is uncertainty regarding the future costs of
both the main materials needed to implement the Swedish deep disposal concept: copper powder for
the canisters and bentonite for the backfill.342
The repository layout will also influence costs due to the cost of constructing and backfilling the
343
tunnels and the costs of the bentonite needed for the disposal holes. For example, placing several
spent fuel canisters in long horizontal disposal drifts is cheaper than excavating individual vertical
disposal holes accessed via tunnels. However, this option is more sensitive to the site geology
344
because a single large fracture zone in a long disposal drift could destroy the whole drift. The
design of a repository in fractured rock may need to be optimised to minimise the number of locations
where water-conducting fractures are intersected.345
Some of the concerns highlighted in the literature review above could be mitigated by changes to the
repository design. However, major changes would have significant impacts on projected costs.

46 September 2010
Examples of proposed changes identified in the literature search include:
l thicker copper canisters
l wider spacing between canisters (to reduce the adverse impacts of high temperatures on
bentonite, or to seek to avoid water-conducting fracture zones)
l purer bentonite (to limit mineral changes with heat)
l increased excavation depth (to limit gas bubbles through higher pressure, increase
groundwater flow return times, give greater protection from glaciation and reduce microbial
activity).
All of the above would increase costs significantly. Increasing depth would also increase the risk of
rock bursts (localised earthquakes) due to the high pressures at depth.

September 2010 47
6. Conclusion
A scientific consensus on deep disposal?

The European Commission Joint Research Centre’s report bases its claim that there is a scientific
consensus on the deep disposal of high-level radioactive wastes on the existence of ‘road maps’
346
towards implementing this option in Finland and Sweden.
The Implementing Geological Disposal of Radioactive Waste Technology Platform states that the
recommendation of the OECD Nuclear Energy Agency’s Radioactive Waste Management Committee
is based on work over several decades by the international scientific and technical community in
which alternatives such as launching nuclear waste into space, ocean dumping, disposal under
continental glaciers, sub-seabed disposal and long-term supervised storage were carefully studied
and discarded.347
However, the existence of road maps and the rejection of other options do not automatically mean
that deep disposal of highly radioactive wastes is safe.
On the contrary, the present report’s review of papers published in peer-reviewed scientific journals
has identified a number of scenarios in which a significant release of radioactivity could occur, with
serious implications for the health and safety of future generations.
The following phenomena could compromise containment in a deep repository:
l The effects of intense heat generated by radioactive decay, and of chemical and physical
disturbance due to corrosion, gas generation and biomineralisation, could impair the ability of
backfill material to trap some radionuclides.
l Build-up of gas pressure in the repository, as a result of the corrosion of metals and/or the
degradation of organic material, could damage the barriers and force fast routes for
radionuclide escape through crystalline rock fractures or clay rock pores.
l Poorly understood chemical effects, such as the formation of colloids, could speed up the
transport of some of the more radiotoxic elements such as plutonium.
l Unidentified fractures and faults, or poor understanding of how water and gas will flow through
fractures and faults, could lead to the release of radionuclides in groundwater much faster
than expected.
l Excavation of the repository will damage adjacent zones of rock and could thereby create fast
routes for radionuclide escape.
l Future generations, seeking underground resources or storage facilities, might accidentally
dig a shaft into the rock around the repository or a well into contaminated groundwater above
it.
l Future glaciations could cause faulting of the rock, rupture of containers and penetration of
surface waters or permafrost to the repository depth, leading to failure of the barriers and
faster dissolution of the waste.

48 September 2010
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259 Chan, T., Stanchell, F.W. 2005. Subsurface hydro-mechanical (HM) impacts of glaciation: Sensitivity to

60 September 2010
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repositories. Journal of Environmental Radioactivity 101: 435-437

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64 September 2010
GeneWatch
UK

Rock Solid - A Scientific Review

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Rock Solid?

A GeneWatch UK consultancy report

Written by Helen Wallace for Greenpeace International

GeneWatch UK consultancy report

GeneWatch UK consultancy report

Executive summary .............................................................................................................7

GeneWatch UK consultancy report

GeneWatch UK consultancy report

List of text boxes

GeneWatch UK consultancy report

Worldwide, thirteen countries are actively pursuing long-term waste management

GeneWatch UK consultancy report

GeneWatch UK consultancy report

GeneWatch UK consultancy report

GeneWatch UK consultancy report

Box 1: Categories of radioactive waste

GeneWatch UK consultancy report

GeneWatch UK consultancy report

2.1. Harmful effects of radioactive wastes

GeneWatch UK consultancy report

Box 4: Health effects of ionising radiation

GeneWatch UK consultancy report

Box 5: Radionuclides and deep geological disposal

GeneWatch UK consultancy report

GeneWatch UK consultancy report

GeneWatch UK consultancy report

3.1. Safety assessment

GeneWatch UK consultancy report

3.2. National programmes for geological disposal

GeneWatch UK consultancy report

GeneWatch UK consultancy report

3.3. Potential for significant radiological releases?

GeneWatch UK consultancy report

GeneWatch UK consultancy report

4.1. Corrosion of canisters, wastes, and repository structures

4.1.1. Corrosion of copper

GeneWatch UK consultancy report

4.1.2. Corrosion of copper by water

4.1.3. Role of microbes

GeneWatch UK consultancy report

4.1.4. Steel corrosion and hydrogen gas generation

GeneWatch UK consultancy report

4.2. Bentonite erosion and loss of buffer capacity

4.2.1. Effects of heat and mineral changes on bentonite

GeneWatch UK consultancy report

GeneWatch UK consultancy report

4.2.2. Effects of saline water

4.2.3. Effects of other minerals in clay

4.2.4. Chemical disturbance due to corrosion

GeneWatch UK consultancy report

4.2.5. Effects of gas on the clay barrier

GeneWatch UK consultancy report

4.2.6. The role of microbes: gas production and biomineralisation

GeneWatch UK consultancy report

4.3. Solubility, sorption and transport of radionuclides

GeneWatch UK consultancy report

4.3.2. Colloids and complexation

4.3.3. The role of microbes

GeneWatch UK consultancy report

4.3.4. Release of radioactive gas

4.3.5. Summary of solubility, sorption and transport of radionuclides

4.4. Bedrock properties and hydrogeology

GeneWatch UK consultancy report

GeneWatch UK consultancy report