The Fukushima Daiichi Incident
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Matthias Braun
PEPA4-G
AREVA NP GmbH

The Fukushima Daiichi Incident
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Unit I - GE Mark I BWR (439 MW), Operating since 1970
Unit II & III - GE Mark I BWR (760 MW), Operating since 1974
Spiegel.de

The Fukushima Daiichi Incident
Service Floor (Steel)
Building (Concrete)
RPV
Containment
Pressure suppression pool nucleartourist.com

The Fukushima Daiichi Incident nucleartourist.com

The Fukushima Daiichi Incident nucleartourist.com

The Fukushima Daiichi Incident nucleartourist.com

The Fukushima Daiichi Incident www.zwentendorf.com

The Fukushima Daiichi Incident nucleartourist.com

The Fukushima Daiichi Incident
Fresh Steam
Main Feedwater
Core
RPV
Containment
Pressure suppression pool

The Fukushima Daiichi Incident
Containment
Pressure suppression pool
Containment closure
Head en.wikipedia.org/wiki/Browns_Ferry_Nuclear_Power_Plant

The Fukushima Daiichi Incident
Progression of the accident:
 11.3.2011 14:46
Earthquake
 SCRAM
 Containment-Isolation
► Close of fresh steam and main feed water valves
► Only a failure of these
Valves could lead to an early large release

The Fukushima Daiichi Incident
 11.3.2011 3:41pm
Station-Blackout
► Loss of off-site power due to Earthquake
► Diesel startet as planed
► Tsunami damaged either
Diesel generators or
Service water supply
(Tsunami height >7m, plant designed for 6.5m)
► Failure of all active cooling systems
 Core Isolation Pump /
Einspeisesystem TJ
► Steam from Reactor drives
Turbine
► Turbine pumps water form pressure suppression pool
► Needs Battery power

The Fukushima Daiichi Incident
 Reactor Isolation pump stopped
► Either Run-out of Batteries
► Or pressure suppression pool boils
 Pressure buildup in reactor
► Decay heat produces steam
 Opening of pressure relief valves
► Steam gets blown in pressure suppression pool

The Fukushima Daiichi Incident
 Dry-out of the RPV

The Fukushima Daiichi Incident
 Dry-out of the RPV

The Fukushima Daiichi Incident
 Dry-out of the RPV

The Fukushima Daiichi Incident
 Dry-out of the RPV

The Fukushima Daiichi Incident
 Dry-out of the RPV
 Heat-up of the exposed fuel

The Fukushima Daiichi Incident
 At ~900 °C
► ~1/3 of Core uncovered
► Fracture of the Cladding
► Release of first fission products
 At ~1200 °C
► ~1/2 of Core uncovered
► Zirconium burns Steam
► Zr + H
2
0 ->ZrO + H
2
► Strong core heat-up
► 300-600kg Hydrogen
► Strong Pressure buildup in containment

The Fukushima Daiichi Incident
 Strong release of fission products
 Xenon
 Cesium
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Iodine
….
► Aerosols (Smoke)
► Large fraction of fission products get scrubbed in pressure suppression pool, not Xenon
► Uranium/Plutonium remain in core
 At ~1800 °C
► Melting of the cladding
► Unknown if this stadium was reached

The Fukushima Daiichi Incident
 Due to hydrogen, pressure build-up up to 8bar in containment
 Venting of containment down to ~4 bar
 Venting via pressure suppression pool removes significant amount of aerosols
► Release of small amounts of Aerosols (Iodine,
Cesium) and
► most of radioactive noble gases (Xenon) and
► Hydrogen

The Fukushima Daiichi Incident
 Vented gas was released inside Reactor service floor
 Hydrogen combustion blows of Service Floor
► Explosion Unit 1:
14.3.2011 11:01AM
► Explosion Unit 3:
14.3.2011 11:01AM
 Concrete Reactor building unaffected
 Explosion of the building spectacular, but minor importance
 Deduced Informations
► Service Floor ~8000m3
► 
100 to 200kg H2
►  20% to 40% Core oxidation dailycaller.com

The Fukushima Daiichi Incident
 Radiation released
► Maximum ~1mSv/h on site after venting of unit 1
► Probably similar dose at
Venting of Site 2
► Expected order of magnitude by German crisis documents
► Rapid falling values to
~0.07mSv
► Indicating main release was noble gases
► INES4 classified
► Most probably no land permanently contaminated

The Fukushima Daiichi Incident
 Current Information
► RPV Flooded by See water in all 3 Units
► Containment flooded at least in Unit 1
► Liquid level stable
 Further cooling of the containment by venting
 Clogging of fuel by sea water?
► Rough estimate after 100h by flooding by pure sea water
 Core status
► Unit1: Core damaged
► Unit2: unknown
► Unit3: Core oxidized, possibly damaged

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Informations supplyed by
Google.com
GRS.de
Yoshiaki Oka, Waseda university

Yoshiaki Oka
Waseda university
Prepared for the presentation at ISSCWR5 on March 14, 2011 from the request of the organizer based on the information until March 13 in Canada. Available Information is very limited. Recovery action is in progress. The presentation may contain misunderstandings.

 Attached northern part of Japan at 2:46pm of March 11, 2011.
 Magnitude is 9 in Richter scale. The biggest in history.
 Some earth quakes occurred along the boundary of plates. Hundreds of km of the boundary moved, similar to the big earth quake in Indonesia.
 Big Tsunami (10m) attacked northern Japan and NPP. It was bigger than expected.
 There is no damage in the central Tokyo.
 Power plants including gas and coal fired ones were automatically shut down.
NPPs were also automatically shut down.

 6 units , Unit #1, #2 , and #3 in trouble.
 Unit #1: 460MWe BWR ,Unit #3,#2: 768MWe BWR
 2:46pm March 11: The earth quake happened. Plants automatically shut down.
Offsite power lost. Emergency DG started up.
 3:41pm Emergency DG stopped due to loss of equipment cooling water.
(Tsunami was bigger than expected.) All AC power was lost and consequential isolation from UHS, except for IC (isolation cooling system) in 1F1. RCIC in 1F
2 Blackout + (mostly) loss of UHS
 RCIC was available to makeup water in the initial stage.
 SAM (Severe Accident Management) prepared in the 90’s in place such as containment scrubbing venting, supply of water from portable water tank using
Fire Protection pump or Fire Engine and inter-connection of power supply with other units.
 Site emergency announced. (After JCO accident, emergency law was settled. It requires report to the central government.) Evacuation up to 20km around 1F,
10km around 2F.

 Loss of All AC power.
 Partial core uncover (1-2m) occurred.
 Hydrogen generated by Zr-water reaction
 CV pressure increased and CVs were vented to maintain the integrity.
 Hydrogen detonation occurred in the upper part of the reactor buildings
(unit 1 on March 12 and unit 2 on March 14). 14 workers injured.
 Area evacuated in 20km.
 Radiation levels are low , 1mSv/h highest at the site. (Dose limit of public:
ImSv/y)
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Sea water with boric acid injected into RPV and CV.
CV integrity is maintained. Large release will be not likely .
Cores are covered by water now.
Level 4 accident of IAEA.

 Loss of all AC power.
 RCIC was in operation but is now lost.
 Low water level in RPV and High CV pressure continue. Mobile power supply is tried but not working well. CV vent my be considered.
 Fuel is covered by water (3am of March 14), but there is a threat to core uncovery.
 Depressurization of RPV, CV venting and Seawater injection are in preparation .

10-20km from site #1
 4 units: 110MWe BWR
 Sea water pumps of unit 1,2 and 4 did not work due to Tsunami. The motors were being replaced unit by unit. Recovery of the cooling were successful for unit 1 at 3am and for unit 2 at 7am of March 14.