Le Document D'areva Sur Fukushima

The Fukushima Daiichi Incident – Dr. Matthias Braun - 27 March 2011 - p.
1
The
Fukushima Daiichi
Incident
1. Plant Design
2. Accident Progression
3. Radiological releases
4. Spent fuel pools
5. Sources of Information
Matthias Braun
PEPA4-G, AREVA–NP GmbH
Matthias.Braun@AREVA.com
The Fukushima Daiichi Incident – Dr. Matthias Braun - 27 March 2011 - p.2
The Fukushima Daiichi Incident
1. Plant Design
Fukushima Daiichi (Plant I)

 Unit I - GE Mark I BWR (439 MW), Operating since 1971
 Unit II-IV - GE Mark I BWR (760 MW), Operating since 1974
1. Plant Design
Building structure
 Concrete Building Containment
 Steel-framed Service Floor  Pear-shaped Dry-Well
 Torus-shaped Wet-Well
en.wikipedia.org/wiki/Browns_Ferry_Nuclear_Power_Plant
nucleartourist.com
1. Plant Design
Service Floor
1. Plant Design
Lifting the Containment

closure head
1. Plant Design
Reactor Service Floor

(Steel Construction) Spend Fuel Pool
Concrete Reactor Building

(secondary Containment)
Fresh Steam line

Main Feedwater
Reactor Core
Reactor Pressure Vessel
Containment (Dry well)
Containment (Wet Well) /

Condensation Chamber
2. Accident progression
11.3.2011 14:46 - Earthquake

 Magnitude 9
 Power grid in northern Japan fails
 Reactors itself are mainly
undamaged
SCRAM
 Power generation due to Fission
of Uranium stops
 Heat generation due to radioactive
Decay of Fission Products
 After Scram ~6%
 After 1 Day ~1%
 After 5 Days ~0.5%
Containment Isolation
 Closing of all non-safety related
Penetrations of the containment
 Cuts off Machine hall
 If containment isolation succeeds,
a large early release of fission
products is highly unlikely
Diesel generators start

 Emergency Core cooling systems
are supplied
Plant is in a stable save state
11.3. 15:41 Tsunami hits the plant

 Plant Design for Tsunami height of
up to 6.5m
 Actual Tsunami height >7m
 Flooding of
 Diesel Generators and/or
 Essential service water building
cooling the generators
Station Blackout
 Common cause failure of the
power supply
 Only Batteries are still available
 Failure of all but one Emergency
core cooling systems
Reactor Core Isolation Pump still

available
 Steam from the Reactor drives a
Turbine
 Steam gets condensed in the
Wet-Well
 Turbine drives a Pump
 Water from the Wet-Well gets
pumped in Reactor
 Necessary:
 Battery power
 Temperature in the wet-well
must be below 100°C
As there is no heat removal from

the building, the Core isolation
pump cant work infinitely
Reactor Isolation pump stops

 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)
Decay Heat produces still steam in

Reactor pressure Vessel
 Pressure rising
Opening the steam relieve valves

 Discharge Steam into the Wet-Well
Descending of the Liquid Level in

the Reactor pressure vessel

 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)

 Pressure rising



 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)

 Pressure rising



 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)

 Pressure rising



 11.3. 16:36 in Unit 1
(Batteries empty)
 14.3. 13:25 in Unit 2
(Pump failure)
 13.3. 2:44 in Unit 3
(Batteries empty)

 Pressure rising


Measured, and here referenced
Liquid level is the collapsed level.
The actual liquid level lies higher
due to the steam bubbles in the
liquid
~50% of the core exposed

 Cladding temperatures rise, but still
no significant core damage
~2/3 of the core exposed

 Cladding temperature
exceeds ~900°C
 Balooning / Breaking of the
cladding
 Release of fission products form
the fuel rod gaps
~3/4 of the core exposed

 Cladding exceeds ~1200°C
 Zirconium in the cladding starts to
burn under Steam atmosphere
 Zr + 2H20 ->ZrO2 + 2H2
 Exothermal reaction further
heats the core
 Generation of hydrogen
 Unit 1: 300-600kg
 Unit 2/3: 300-1000kg
 Hydrogen gets pushed via the
wet-well, the wet-well vacuum
breakers into the dry-well
at ~1800°C [Unit 1,2,3]
 Melting of the Cladding
 Melting of the steel structures
at ~2500°C [Block 1,2]

 Breaking of the fuel rods
 debris bed inside the core
at ~2700°C [Block 1]
 Melting of Uranium-Zirconium
eutectics
Restoration of the water supply

stops accident in all 3 Units
 Unit 1: 12.3. 20:20 (27h w.o. water)
 Unit 2: 14.3. 20:33 (7h w.o. water)
 Unit 3: 13.3. 9:38 (7h w.o. water)
Release of fission products during

melt down
 Xenon, Cesium, Iodine,…
 Uranium/Plutonium remain in core
 Fission products condensate to
airborne Aerosols
Discharge through valves into water

of the condensation chamber
 Pool scrubbing binds a fraction of
Aerosols in the water
Xenon and remaining aerosols

enter the Dry-Well
 Deposition of aerosols on surfaces
further decontaminates air
Containment
 Last barrier between Fission
Products and Environment
 Wall thickness ~3cm
 Design Pressure 4-5bar
Actual pressure up to 8 bars

 Normal inert gas filling (Nitrogen)
 Hydrogen from core oxidation
 Boiling condensation chamber
(like a pressure cooker)
Depressurization of the
containment
 Unit 1: 12.3. 4:00
 Unit 2: 13.3 00:00
 Unit 3: 13.3. 8.41
Positive und negative Aspects of

depressurizing the containment
 Removes Energy from the Reactor
building (only way left)
 Reducing the pressure to ~4 bar
 Release of small amounts of
Aerosols (Iodine, Cesium ~0.1%)
 Release of all noble gases
 Release of Hydrogen
Gas is released into the reactor

service floor
 Hydrogen is flammable
Unit 1 und 3
 Hydrogen burn inside the reactor
service floor
 Destruction of the steel-frame roof
 Reinforced concrete reactor
building seems undamaged
 Spectacular but minor safety
relevant
Unit 2
 Hydrogen burn inside the reactor
building
 Probably damage to the
condensation chamber
(highly contaminated water)
 Uncontrolled release of gas from
the containment
 Release of fission products
 Temporal evacuation of the plant
 High local dose rates on the plant
site due to wreckage hinder further
recovery work
No clear information's why Unit 2

behaved differently
Current status of the Reactors

 Core Damage in Unit 1,2, 3
 Building damage due to various
burns Unit 1-4
 Reactor pressure vessels flooded
in all Units with mobile pumps
 At least containment in Unit 1
flooded
Further cooling of the Reactors by

releasing steam to the atmosphere
Only small further releases of

fission products can be expected
Directly on the plant site

 Before Explosion in Unit Block 2
 Below 2mSv / h
 Mainly due to released radioactive noble gases
 Measuring posts on west side. Maybe too small values measured due to wind
 After Explosion in Unit 2 (Damage of the Containment)

 Temporal peak values 12mSv / h
 (Origin not entirely clear)
 Local peak values on site up to 400mSv /h (wreckage / fragments?)
 Currently stable dose on site at 5mSv /h
 Inside the buildings a lot more
 Limiting time of exposure of the workers necessary
Outside the Plant site

 As reactor building mostly intact
=> reduced release of Aerosols (not Chernobyl-like)
 Fission product release in steam
=> fast Aerosol grows, large fraction falls down in the proximity of the plant
 Main contribution to the radioactive dose outside plant are the radioactive
noble gases
 Carried / distributed by the wind, decreasing dose with time
 No „Fall-out“ of the noble gases, so no local high contamination of soil
~20km around the plant

 Evacuations were adequate
 Measured dose up to 0.3mSv/h for short times
 Maybe destruction of crops / dairy products this year
 Probably no permanent evacuation of land necessary
GRS.de
~50km around the plant

 Control of Crop / Dairy products
 Usage of Iodine pills
(Caution, pills can interfere
with heart medicine)
4. Spend fuel pools
Spend fuel stored in Pool on

Reactor service floor
 Due to maintenance in Unit 4 entire
core stored in Fuel pool
 Dry-out of the pools
 Unit 4: in 10 days
 Unit 1-3,5,6 in few weeks
 Leakage of the pools due to
Earthquake?
Consequences
 Core melt „on fresh air “
 Nearly no retention of fission
products
 Large release
4. Spend fuel pools

Earthquake?
Consequences
products
 Large release
4. Spend fuel pools

Earthquake?
Consequences
products
 Large release
It is currently unclear if release

from fuel pool already happened
5. Sources of Information
Good sources of Information

 Gesellschaft für Reaktorsicherheit [GRS.de]
 Up to date
 Radiological measurements published
 German translation of japanese/englisch web pages
 Japan Atomic Industrial Forum [jaif.or.jp/english/]

 Current Status of the plants
 Measurement values of the reactors (pressure liquid level)
 Tokyo Electric Power Company [Tepco.co.jp]

 Status of the recovery work
 Casualties
May too few information are released by TEPCO, the operator of the plant

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The Fukushima Daiichi Incident – Dr. Matthias Braun - 27 March 2011 - p.

Fukushima Daiichi (Plant I)

Lifting the Containment

Reactor Service Floor

Concrete Reactor Building

Fresh Steam line

Reactor Pressure Vessel

Containment (Dry well)

Containment (Wet Well) /

11.3.2011 14:46 - Earthquake

Diesel generators start

Plant is in a stable save state

11.3. 15:41 Tsunami hits the plant

Reactor Core Isolation Pump still

As there is no heat removal from

Reactor Isolation pump stops

Decay Heat produces still steam in

Opening the steam relieve valves

Descending of the Liquid Level in

Reactor Isolation pump stops

Decay Heat produces still steam in

Opening the steam relieve valves

Descending of the Liquid Level in

Reactor Isolation pump stops

Decay Heat produces still steam in

Opening the steam relieve valves

Descending of the Liquid Level in

Reactor Isolation pump stops

Decay Heat produces still steam in

Opening the steam relieve valves

Descending of the Liquid Level in

Reactor Isolation pump stops

Decay Heat produces still steam in

Opening the steam relieve valves

Descending of the Liquid Level in

~50% of the core exposed

~2/3 of the core exposed

~3/4 of the core exposed

at ~2500°C [Block 1,2]

Restoration of the water supply

Release of fission products during

Discharge through valves into water

Xenon and remaining aerosols

Actual pressure up to 8 bars

Positive und negative Aspects of

Gas is released into the reactor

No clear information's why Unit 2

Current status of the Reactors

Further cooling of the Reactors by

Only small further releases of

Directly on the plant site

 After Explosion in Unit 2 (Damage of the Containment)

 Limiting time of exposure of the workers necessary

Outside the Plant site

~20km around the plant

~50km around the plant

Spend fuel stored in Pool on

Spend fuel stored in Pool on

Spend fuel stored in Pool on

It is currently unclear if release

Good sources of Information

 Japan Atomic Industrial Forum [jaif.or.jp/english/]

 Tokyo Electric Power Company [Tepco.co.jp]