Le document d'Areva sur Fukushima

8/7/2019 Le document d'Areva sur Fukushima

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The Fukushima Daiichi Incident Dr. Matthias Braun - 27 March 2011 - p.1


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The

Fukushima DaiichiIncident

1. Plant Design2. Accident Progression3. Radiological releases4. Spent fuel pools5. Sources of Information

Matthias BraunPEPA4-G, AREVA NP [email protected]


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The Fukushima Daiichi Incident1. Plant Design

Fukushima Daiichi (Plant I)

Unit I - GE Mark I BWR (439 MW), Operating since 1971Unit II-IV - GE Mark I BWR (760 MW), Operating since 1974


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Building structureConcrete Building

Steel-framed Service Floor

Containment

Pear-shaped Dry-WellTorus-shaped Wet-Well


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Service Floor


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Lifting the Containment

closure head


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Reactor Service Floor

(Steel Construction)

Concrete Reactor Building(secondary Containment)

Reactor Core

Reactor Pressure Vessel

Containment (Dry well)

Containment (Wet Well) / Condensation Chamber

Spend Fuel Pool

Fresh Steam line

Main Feedwater


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The Fukushima Daiichi Incident2. Accident progression

11.3.2011 14:46 - EarthquakeMagnitude 9

Power grid in northern Japan fails

Reactors itself are mainlyundamaged

SCRAMPower generation due to Fissionof Uranium stops

Heat generation due to radioactive

Decay of Fission ProductsAfter Scram ~6%After 1 Day ~1%After 5 Days ~0.5%


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Containment Isolation

Closing of all non-safety relatedPenetrations of the containment

Cuts off Machine hall

If containment isolation succeeds,a large early release of fissionproducts is highly unlikely

Diesel generators startEmergency Core cooling systemsare supplied

Plant is in a stable save state


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11.3. 15:41 Tsunami hits the plantPlant Design for Tsunami height ofup to 6.5m

Actual Tsunami height >7m

Flooding ofDiesel Generators and/or

Essential service water buildingcooling the generators

Station BlackoutCommon cause failure of thepower supply

Only Batteries are still available

Failure of all but one Emergencycore cooling systems


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Reactor Core Isolation Pump still

availableSteam from the Reactor drives aTurbine

Steam gets condensed in theWet-Well

Turbine drives a Pump

Water from the Wet-Well getspumped in Reactor

Necessary:Battery powerTemperature in the wet-wellmust be below 100C

As there is no heat removal fromthe building, the Core isolationpump cant work infinitely


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Reactor Isolation pump stops

11.3. 16:36 in Unit 1(Batteries empty)

14.3. 13:25 in Unit 2(Pump failure)


Decay Heat produces still steam inReactor pressure Vessel

Pressure rising

Opening the steam relieve valvesDischarge Steam into the Wet-Well

Descending of the Liquid Level inthe Reactor pressure vessel


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Pressure rising




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Pressure rising




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Pressure rising




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Pressure rising




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Measured, and here referenced

Liquid level is the collapsed level.The actual liquid level lies higherdue to the steam bubbles in theliquid

~50% of the core exposedCladding temperatures rise, but stillno significant core damage

~2/3 of the core exposed

Cladding temperatureexceeds ~900C

Balooning / Breaking of thecladding

Release of fission products formthe fuel rod gaps


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~3/4 of the core exposedCladding exceeds ~1200C

Zirconium in the cladding starts toburn under Steam atmosphere

Zr + 2H 20 ->ZrO 2 + 2H 2

Exothermal reaction furtherheats the core

Generation of hydrogenUnit 1: 300-600kgUnit 2/3: 300-1000kg

Hydrogen gets pushed via thewet-well, the wet-well vacuumbreakers into the dry-well


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at ~1800C [Unit 1,2,3]Melting of the Cladding

Melting of the steel structures

at ~2500C [Block 1,2]Breaking of the fuel rods

debris bed inside the core

at ~2700C [Block 1]Melting of Uranium-Zirconiumeutectics

Restoration of the water supplystops 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)


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Release of fission products duringmelt downXenon, Cesium, Iodine,

Uranium/Plutonium remain in core

Fission products condensate toairborne Aerosols

Discharge through valves into waterof the condensation chamber

Pool scrubbing binds a fraction ofAerosols in the water

Xenon and remaining aerosolsenter the Dry-Well

Deposition of aerosols on surfacesfurther decontaminates air


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ContainmentLast barrier between Fission

Products and EnvironmentWall 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 thecontainment

Unit 1: 12.3. 4:00

Unit 2: 13.3 00:00

Unit 3: 13.3. 8.41


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Positive und negative Aspects ofdepressurizing the containmentRemoves Energy from the Reactorbuilding (only way left)

Reducing the pressure to ~4 bar

Release of small amounts ofAerosols (Iodine, Cesium ~0.1%)Release of all noble gases

Release of Hydrogen

Gas is released into the reactor

service floorHydrogen is flammable


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Unit 1 und 3

Hydrogen burn inside the reactorservice floor

Destruction of the steel-frame roof

Reinforced concrete reactorbuilding seems undamaged

Spectacular but minor safetyrelevant


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Unit 2

Hydrogen burn inside the reactorbuilding

Probably damage to thecondensation chamber(highly contaminated water)

Uncontrolled release of gas from

the containmentRelease of fission products

Temporal evacuation of the plant

High local dose rates on the plantsite due to wreckage hinder furtherrecovery work

No clear information's why Unit 2behaved differently


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Current status of the Reactors

Core Damage in Unit 1,2, 3Building damage due to variousburns Unit 1-4

Reactor pressure vessels floodedin all Units with mobile pumps

At least containment in Unit 1flooded

Further cooling of the Reactors byreleasing steam to the atmosphere

Only small further releases offission products can be expected


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The Fukushima Daiichi Incident3. Radiological releases

Directly on the plant siteBefore Explosion in Unit Block 2

Below 2mSv / hMainly due to released radioactive noble gasesMeasuring 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 /hInside the buildings a lot more

Limiting time of exposure of the workers necessary


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Outside the Plant siteAs 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 gasesCarried / 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 adequateMeasured dose up to 0.3mSv/h for short times

Maybe destruction of crops / dairy products this year

Probably no permanent evacuation of land necessary


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GRS.de

~50km around the plantControl of Crop / Dairy products

Usage of Iodine pills(Caution, pills can interferewith heart medicine)


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The Fukushima Daiichi Incident4. Spend fuel pools

Spend fuel stored in Pool on

Reactor service floorDue to maintenance in Unit 4 entirecore stored in Fuel pool

Dry-out of the poolsUnit 4: in 10 daysUnit 1-3,5,6 in few weeks

Leakage of the pools due toEarthquake?

ConsequencesCore melt on fresh air

Nearly no retention of fissionproducts

Large release


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Large release


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Large release

It is currently unclear if releasefrom fuel pool already happened


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h k h h d h h

The Fukushima Daiichi Incident5. Sources of Information

Good sources of InformationGesellschaft fr Reaktorsicherheit [GRS.de]

Up to dateRadiological measurements publishedGerman translation of japanese/englisch web pages

Japan Atomic Industrial Forum [jaif.or.jp/english/]Current Status of the plantsMeasurement values of the reactors (pressure liquid level)

Tokyo Electric Power Company [Tepco.co.jp]Status of the recovery workCasualties

May too few information are released by TEPCO, the operator of the plant

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