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7/31/2019 Overview Ofthe Fukushima Daiichi Accident
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IAEAInternational Atomic Energy Agency
Overview of
the Fukushima Daiichi Accident
Consultants Meeting on the Status of
Innovative Small and Medium sized Reactor (SMR)
Technology and Designs with the Potential for Near Term Deployment
02-04 May 2011
Katsumi Yamada
Figures and photos are fromthe websites of GE-HitachiNuclear Energy, JAIF, NISA,NRC, SFEN, and TEPCO.
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OUTLINE
Fukushima Daiichi Nuclear Power Station
BWR Technologies and systems Pressure Suppression Containment
Emergency Core Cooling System (ECCS) Event Sequence
External Events (Earthquake/Tsunami)
Plant Responses and Actions Preliminary Lessons Learned
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NPPs in Japan
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Fukushima Daiichi Nuclear
Power Station
http://upload.wikimedia.org/wikipedia/commons/3/32/Japan_Nuclear_power_plants_map.gifhttp://upload.wikimedia.org/wikipedia/commons/3/32/Japan_Nuclear_power_plants_map.gif7/31/2019 Overview Ofthe Fukushima Daiichi Accident
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Fukushima Daiichi Nuclear Power Station
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Unit #Reactor
Type
Containment
Type
Electric
Power(Gross)
Commercial
Operation
Main
Contractor Status at theEarthquake
Unit-1 BWR/3 MARK-I 460 MWe 1971 GE In power
Unit-2 BWR/4 MARK-I 784 MWe 1974 GE/Toshiba In power
Unit-3 BWR/4 MARK-I 784 MWe 1976 Toshiba In power
Unit-4 BWR/4 MARK-I 784 MWe 1978 HitachiRefueling
Outage
Unit-5 BWR/4 MARK-I 784 MWe 1978 ToshibaRefueling
Outage
Unit-6 BWR/5 MARK-II 1100 MWe 1979 GE/ToshibaRefueling
Outage
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BWR/4 with Mark I Containment
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MARK-I Pressure Suppression Containment
MARK-I Containment consists of a drywell and a wetwell. The drywell is a bulb-shape vessel made of steel and
encloses the Reactor Vessel.
The wetwell is a torus with a large amount of water pool
called Suppression Pool, where steam is injected andcondensed to suppress the pressure increase.
Steam comes from the drywell through vent pipes (in caseof LOCA) and/or from the reactor vessel via safety/relief
valves. Vacuum breakers permit flow back from the wetwell to the
drywell if the drywell pressure is reduced.
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BWR/4 during Normal Operation
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BWR/4 Emergency Core Cooling System
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ECCS- HPCI
- 2CS
- 2LPCI (RHR)
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Events Sequence since 11 March(Fukushima Daiichi NPS Unit 3)
External Event Internal Event and Action
Earthquake (M9.0) Reactor Automatic Shutdown (Scram)
Loss of
off-site PowerDiesel Generators Automatic Start
March 11
14:46
Tsunami (14 - 15m)
All AC Power Loss (Station Black Out)
Water Injection by RCIC/HPCI
Loss of Core Cooling
: Favorable (Designed) Response
: Unfavorable Response
15:42
March 13
05:10
9
Diesel Generators Stopped
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Seaside Components after Tsunami (Daiichi)
10
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Tsunami (Fukushima Daini NPS)
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Before Tsunami
Inundating Tsunami
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Engineered Safety System: HPCI/ADS
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High Pressure Coolant Injection System (HPCI)
Automatic Depressurization System (ADS)
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Engineered Safety System: CS/LPCI
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Low pressure coolant Injection System (LPCI)
Core Spray System (CS)
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Hydrogen
Explosion
PCV Pressure
Increase
Loss of Core Cooling
Core Water Level
Decrease
PCV (S/C)
Venting Start
Alternate Water Injection by
Fire-Extinguishing System
Fuel Uncovery
Fuel DamageFission Product
Release
March 14
11:01
:: Action based on Accident Management Guidelines
External Event Internal Event and Action
Events Sequence since 11 March (contd)(Fukushima Daiichi NPS Unit 3)
March 13
05:10
March 13
08:41
March 14
05:20
March 13
13:12
Hydrogen
Accumulation ?
?
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Unit 3 after Explosion (April 10)
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Preliminary Lessons Learned : Design Aspect
What were good All control rods were inserted into the core successfully
in spite the acceleration exceeded the expectation.
The diesel generators started automatically.
RCIC and HPCI worked without AC power and cooledthe core for the first 1.5 days.
Accident Management (AM) was considered andprepared in advance.
AM Guidelines preparedPCV vent and alternate water injection systems installed
Operators trained
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What were not good All off-site powers were lost simultaneously.
The height of tsunami exceeded the expectation anddestroyed the seaside structures and components.
All diesel generators stopped due to the tsunami (SBO).
It took more time to supply electricity than the lifetime ofDC batteries.
Hydrogen was accumulated in the R/B and exploded.
(Source and leakage path has not been identified.)
Ultimate heat sink has been lost.
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Preliminary Lessons Learned : Design Aspect
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Current Priorities
Six Project Teams have been established under theIntegrated Headquarters:
1) Radiation Shielding/Radioactive Materials Release Reduction
2) Defuelling/Fuel Transportation
3) Remote Monitoring/Sampling4) Long Term Cooling Circuit Establishment
5) Contaminated Water Management
6) Environmental Impact evaluation
TEPCOs current priorities are on 4) and 5), and onPower System Recovery, which is the basis of allactivities.
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Integrated Headquarters meeting
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Daily Meeting at Emergency Center
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Future Plans
TEPCO Chairmans Announcement on 17 April The 1st Stage (in 3 months):
Cool the reactors in a stable manner; and
Prevent water with high levels of radioactivity from flowing out ofthe plant.
The 2nd Stage (in 6 to 9 months):
Achieve a cold shutdown of the reactors; and
Reduce the total amount of radioactive water.
Chief Cabinet Secretary approved the plan as sufficiently
feasible.
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Thank you for your attention!
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