Accident Management on Fukushima Accident and Advanced ABWR

© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.

Accident Management on Fukushima Accident and Advanced ABWR

2012-08-29 Hitachi-GE Nuclear Energy, Ltd. Kenichi YASUDA

AE-OG-5531 Rev.0

5th INPRO Dialogue Forum on Global Nuclear Energy Sustainability 27-31 August 2012, COEX, Seoul, Republic of Korea


Table of Contents

1

1. Introduction

2. Analysis of Fukushima Accident

3. Lessons Learned

4. ABWR Features

5. Countermeasures

6. Evaluation of Countermeasures

7. Conclusion


1. Introduction

2

Fukushima site was inundated by the large tsunami, on

March 11, 2011, which resulted in extensive damage to site

existing facilities and complete loss of AC powers, so called

SBO (Station Blackout), and loss of heat removal systems.

In relation to the emergency procedure in SBO, several

lessons learned have been discussed.

In this presentation, this accident is summarized in the view

point of effectiveness of existing countermeasures and

emergency operations. Then, design enhancements for

ABWR are discussed, which strengthen the robustness for

severe accidents.


2. Analysis of Fukushima Daiichi Accident [1/4]

3

Huge Earthquake (the world 4th biggest： M9.0 Richter)

Operating reactors have been stopped by control rods as planned. Offsite-power has been inoperable due to the earthquake. Emergency Diesel Generators(D/Gs) have started as planned.

Huge Tsunami attack (Estimated about 14m)

DC batteries, D/Gs, Seawater pumps, etc. Inoperable due to Tsunami flood

■ Loss of DC power ; lost DC power source for depressurization and cooling ■ Long-term SBO (Station Black Out of electricity) ; lost the AC power source for cooling ■ LUHS (Loss of normal ultimate heat sink) ; could not remove decay heat

■ Loss of DC power , Long-term SBO and LUHS caused by

Tsunami led to the Accident


Loss of DC power, extended (about 1 week) SBO and

LUHS caused Loss of Cooling function


4

RPV

PCV

CRs

Shutdown

Cooling

Containment

worked

Not worked

Partly failed

Hx.

Filtered water Storage tank

Condensate Storage tank

Fire engine : Loss of DC power

: SBO, Loss of water : LUHS



5

SBO

Cool Shutdown

N

Y Containment cooling (Including containment vent)

High Pressure Injection

1

4 If PCV cooling necessary

Automatic Start by low core water level

Operator action after confirming low

pressure injection system operation

Automatic Start

2

1

3

4 5

RPV pressure

Elapsed time SBO Col d Shutdown

SCRAM

Low Pressure Injection

3

Residual Heat Removal

5

Depressurization of RPV

2

・HCU

・RCIC ・HPCF×2

・ADS×7

・PCV spray ・PCV vent system

・RHR×3

1

2

・LPFL×3 3

4

5

Abbreviations ADS： Automatic Depressurization System HCU： Hydraulic Control Unit HPCF： High Pressure Core Flooder LPFL： Low Pressure Flooder System

RCIC： Reactor Core Isolation Cooling System RHR： Residual Heat Removal System SBO： Station Black Out

Back up by alternative Injection systems (Accident Management)

Back up by alternative Injection systems (Accident Management)

Back up by alternative standby reactivity control systems (Accident Management)



6

Fission product release route estimate – Core is heated up by loss of all water injection. Then, the temperature of

containment rises by high temperature gas from heated core/debris and

damages the non-metal potion of containment, such as top head flange.

– Background of dose rate increases before first W/W venting and background

level is not rising at the time of W/W venting. Therefore, the other causes like

Unit 2 pressure drop has the potential to contributes land contamination.

2)Unit1 W/W Venting

4)Unit1 Building explosion

2)Unit 3 W/W Venting

4)Unit 3 Building Explosion

3)Unit2 PCV pressure decrease

1) Dose rate increase before W/W venting

2) Small imapct on background by W/W venting

3) Background increase Unit 2 PCV pressure drop

Monitoring Car Dose rate

Time W/W Venting

PCV top head

Release route from overtemperature of PCV top flange

Main stuck


Accident management countermeasures have been prepared

for beyond design base accident. However, we faced further

severe condition beyond assumed condition at Fukushima

Daiichi. – Safety concept for unexpected circumstances

– Organization, education, and drills for flexibility

Especially, plant facility and accident management facility

have limitations for site wide damage like Fukushima Daiichi. – Multiple safety measures focusing on on-site and off-site team/resources

– Identification of each personnel’s role and preparation for ordinary time

Accident management equipments did not work effectively at

unexpected circumstances. – Flexible and operable accident management for wide ranging situation

– Believability for monitoring parameters for initial motion

3. Lessons Learned

7


Reactor Internal Pump

• High safety • Simplicity

• High reliability • High operability

Fine Motion Control Rod Drive

Emergency Core Cooling System

• Reduced capacity • High safety

Turbine Generator • High thermal efficiency • Reheat cycle

• Short construction period • Low construction cost

Reinforced Concrete Containment Vessel Reactor Building

• Compact building • Strong structure for vibration

• Improved core • Improved internals

Reactor Pressure Vessel, Core

Main Control Room

• Automatic shorten startup • Fully digital system

4. ABWR: Main Features

8


4. ABWR: Safety Features

9

4 channel reactor protection systems

2 out of 4 digital logic

Three independent divisional ECCS(Emergency Core Cooling Systems)

High Pressure/Low Pressure configuration

3 on-site diesel generator units

Three divisional RHRs

HPCF

LPFL/RHR

DG

HPCF

LPFL/RHR

DG

RCIC

LPFL/RHR

DG

ADS

ABWR Safety System Configuration

RCIC: Reactor Core Isolation Cooling system HPCF: High Pressure Core Flooder system LPFL: Low Pressure Flooder system RHR: Residual Heat Removal system ADS: Automatic Depressurization system DG: Diesel Generator unit

1,350 MWe class

© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved. 10

(2) Cooling and Residual Heat Removal

(1) Power ・DC for initial motion ・Diversified power (GTG or air cooling type DG & Power supply truck) ・Plot plan and GA for large tsunami

補給水源

(5) Emergency Backup Building クーリングタワー

循環ポンプ

補給水源

補給水ポンプ

◆Air cooling heat removal system

B/B

T/B R/B

◆Mobile heat removal system

・Diversified water injection system and Mobile pump for mobility enhancement ・Diversified heat sink by air cooling heat removal system

(3) Prevention for Containment Overtemperature

・Enhancement of PCV cooling function

(4) Spent Fuel Pool Cooling

・Multiple water supply system ・Outside connection for water supply

RCICバッテリ

RCIC制御装置

L/C M/C

非常用発電機

蓄電池

軽油タンク非常用D/G(B)

代替冷却用ポンプ

空冷冷却機

非常用操作盤

非常用D/G(A)

4. ABWR: Additional countermeasures candidates


5. Countermeasures

11

For new construction plants, SBO related systems, including power systems, should be protected from external hazards, such as earthquake and flooding.

– Water tight doors installation to R/B, T/B, C/B

– Physically protection of SBO related systems from external hazards

– Water sources preparation

Following events and condition are considered to develop accident management strategy;

– Loss of all indicators,

– Loss of DC power, and

– Core damage.


5. Countermeasures

12

For preparation for condition described in the previous slide, the following plans are important.

– Mobile plan,

– Flexibility plan, and

– Containment margin development plan


5.1 Mobile Plan

13

Existing accident management enhancement

約12000 2650

2700

冷却用配管出口側（新規追設）

出口側

入口側

ＲＨＲへ

冷却用配管入口側（新規追設）

代替冷却装置外観

冷却用配管外観

Ｔ/Ｂ

ヤード

ＲＨＲより

代替海水ポンプ

部はホース接続

海

Hx

ポンプ

代替Hx(海水側)入口へ

代替Hx(海水側)出口より

代替Hx(淡水側)入口へ

代替Hx(淡水側)出口より

約12000 2650

2700

約12000 2650

2700

冷却用配管出口側（新規追設）

出口側

入口側

ＲＨＲへ

冷却用配管入口側（新規追設）

代替冷却装置外観

冷却用配管外観

Ｔ/Ｂ

ヤード

ＲＨＲより

代替海水ポンプ

部はホース接続

海

Hx

ポンプ

代替Hx(海水側)入口へ

代替Hx(海水側)出口より

代替Hx(淡水側)入口へ

代替Hx(淡水側)出口より

Decay heat removal support from off-site

＋

RHR

FP pump

MUWC pump

CST

Alternative water injection to RPV

W/W: Wet-Well

W/W W/W

For external event, mobile plan considering integration of plant team, on-site team, and off-site team is developed.

To share the strategy, simple core cooling strategy is appropriate in the view point of effectiveness.


原子炉圧力容器（RPV）

ドライウェル（D/W） SRV

Containment

RHR熱交換器

RHR ポンプ

RCW-Hx

原子炉補機冷却海水系（RSW）

原子炉補機冷却水系（RCW）

RSW-P

RCW-P RHR-P冷却器 RHR-P室空調機

その他負荷

主蒸気系(MS)

給水系(FDW)

ウェットウェル（W/W）

所員用エアロック

サプレッションプール(S/P)

換気空調系へ

R/Bから

排気筒

非常用ガス処理系（SGTS)

AC系

燃料プール

PCV spray line

SFP injection line

RHR（B）系

Mobile RCW

Hx

W/Wベントライン

R/B

Mobile pump connection

フィルターベント

Separate layout on outside connections

Maneuverable equipments

Mechanical remote handle

Shield

Equipments with accessibility

14

5.2 Flexibility Plan

Mobile pump connection


5.3 Containment margin development plan

15

Containment boundary margin enhancement

Reactor well flooding

Strengthen of PCV top head flange study

Strengthen of electrical penetrations study

0

100

200

300

400

500

600

0 20 40 60 80 100 120

温度(℃）

PCV内面からの距離(mm)

Mass Ratio 0.1

Mass Ratio 1.3

Mass Ratio 10

Mass Ratio 50


5.4 Enhanced Safety Features for External Hazard

16

“Backup building” has three major functions; – Protection of sets of mobile equipments from external hazards,

– Fire trucks, Power trucks, Alternative heat removal trucks.

– Corporation base for onsite and offsite team, and

– Alternate water injection pump with water sources and power sources.

Reactor Building

Backup Building

Mobile Batteries Power trucks Fire trucks Air fin DG Flooder system Remote control


Loss ofOff-sitePower

SCRAMAC

Power(EDG)

AFCDG

SRVopen

SRVclose

HPCF or

RCIC

ReactorDepressuri zatio

n

Alternat ive

In ject ion

FLSor

Mobi lepump

RHR(alternat

iveRCW)

PCVVenting

Gr. Note

success OK

success OK

OK

OK

OK

OK

OK

OK

6. Evaluation of Countermeasures

17

Alternative AC power

Depressurization: Dedicated battery, etc.

Decay heat removal: Alternative RCW

Decay heat removal: PCV venting

Mobile Pumps

Alternative Water Injection


Understandings of plant conditions of Fukushima accident are; – Loss of all indicators,

– Loss of DC power, and/or

– Core damage.

Lessons Learned from Fukushima accident on accident management are; – Accident management strategy for on and off-site team,

– Accessibility and operability under core damage condition, and

– Protection of mitigation system/equipments from external hazards.

7. Conclusion [1/2]

18


7. Conclusion [2/2]

19

The simple strategy, “Direct core cooling and venting strategy for feed and bleed” is chosen to share among on-site team and off-site team.

Additional enhanced safety in ABWR is built by; – Protecting safety systems from external hazards,

– Providing accessibility and operability, and

– Preparing mobile equipments for above strategy.

To enhance above strategy and the core damage prevention capacity by following items strengthen the plant safety. – Backup building to protect mobile equipments from external

hazards, and

– Dedicated alternative water injection system to RPV in the backup building.



Ref. Plant parameter Enhancement

21

TE P

TE (2) Over range Temperature resistant TE addition for validity standard of other TE

(3) Believability: Low Tech. Bourdon tube pressure measurement

(1) Believability Temperature measurement on water level instrumentation line

(4) Power supply for instrumentation

TE

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Accident Management on Fukushima Accident and Advanced ABWR

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