accident management on fukushima accident and advanced abwr
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© 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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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.
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
Loss of DC power, extended (about 1 week) SBO and
LUHS caused Loss of Cooling function
2. Analysis of Fukushima Daiichi Accident [2/4]
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
2. Analysis of Fukushima Daiichi Accident [3/4]
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)
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
2. Analysis of Fukushima Daiichi Accident [4/4]
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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.
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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.
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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.
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
© Hitachi-GE Nuclear Energy, Ltd. 2012. All rights reserved.
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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