overview ofthe fukushima daiichi accident

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.gif


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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)

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Tsunami (Fukushima Daini NPS)

11

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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overview ofthe fukushima daiichi accident

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