Safety Enhancement Based on the Lessons learned from the Fukushima Accident

Transcription

1 Safety Enhancement Based on the Lessons learned from the Fukushima Accident March 27, IAEA Technical Meeting on Operational Experience with Implementation of Post-Fukushima Actions in NPP Akira KAWANO

2 The Great East Japan Earthquake of March 11, 2011 Earthquake Mw 9.0: the largest earthquake recorded in Japan Plate movement in a wide (200km) and long (500km) area No significant damage or loss of safety systems Tsunami Max. height: 13~15m (design: 6.1m) Almost entire site area was flooded Loss of all AC and DC power supplies (no instrumentations) Loss of ultimate hear sink 1

3 Damage to Fukushima Daiichi NPS Unit 5 sea side seawater pump area Unit 1 containment seawater cooling system pump Confirmation result for the main flooding route by on-site confirmation surrounding the building (1) Building entry/exit (2) Equipment hatch (3) Emergency D/G air supply louver (4) Trench, duct (penetration of cables) etc. Flooding of D/G, electric panel room etc. through these. Unit 1 D/G (1B) Unit 1 power panel at turbine building level 1 Tokyo Electric Power Company, Inc. All Rights 2

4 Accident at Fukushima Daiichi NPS Serious core damage (melt through) of Unit 1-3 Damage of the PCV of Unit 1-3 (Significant amount of radio nuclide release from these Units) Explosion of the reactor building of Unit 1, 3 and 4 Evacuation of about 160,000 local residents 3

5 Overview of the 10-Unit Simultaneous Accidents Date 3/11 3/12 3/13 3/14 3/15 Fukushima Daiichi (1F) Fukushima Daini (2F) /11 15:27 1 st Tsunami, 15:35 2 nd Tsunami 3/11 15:22~ Tsunamis Station Blackout Water Injection: NO Heat Removal: NO 3/12 15:36 Unit 1 Explosion 3/14 11:01 Unit 3 Explosion 3/12 8:13 D/G-6B 3/15 6:00-6:10 Unit 4 Explosion Water Injection: YES Heat Removal: NO 3/14 1:24 RHR 3/14 17:00 3/14 7:13 RHR 3/14 18:00 3/12 12:15 Loss of Ultimate Heat Sink 3/14 15:42 RHR 3/15 7:15 3/ /19 5:00 RHR 3/19 22:14 RHR 3/20 3/20 15:46 P/C-2C 3/20 15:46 P/C-2C 3/22 10:36 P/C-4D 3/22 10:35 P/C-4D 3/20 14:30 3/20 14:30 Water Injection: YES Heat Removal: YES Cold Shutdown 4

6 Lessons Learned from the Fukushima Daiichi Accident Protection against a tsunami exceeding assumption was weak Sufficient preparations were not made for - preventing station blackout (SBO) - mitigating the influence of SBO by ensuring high-pressure core injection, depressurization, low pressure core injection, heat removal Measures were not well prepared to mitigate the impact after reactor core damage : prevention of containment failure hydrogen control countermeasures for core melt-through prevention of a large release of radioactive material into the environment, etc. 5

7 Basic Policies for Reactor Safety Enhancement 1. Reinforce defense in depth against external events 2. Adopt a concept of Phased Approach to emergency response 3. Ensure integrity of Containment Vessel in severe accidents 6

8 Basic Policies for Reactor Safety Enhancement (Continued) 1. Reinforcement of defense in depth against external events Reinforce defense in depth based on the assumption that multiple function failures could be caused by external events Establish safety measures along with defense in depth concept focusing on diversity and physical separation Consider not only earthquake and tsunami but also 40 natural events and 20 human induced external events shown in US NUREG* and the IAEA Safety Guide** Select the external events based on their cliff edge effect and their probability, and establish safety measures against them Strengthen measures also against internal flooding and internal fire Use of probabilistic risk assessment (PRA) to: select accident sequences to be evaluated confirm effectiveness of the established safety measures * NUREG/CR-2300 Vol.2, PRA Procedures Guide ** IAEA Specific Safety Guide SSG-3, Development and Application of Level 1 Probabilistic Safety Assessment for Nuclear Power Plants 7

9 Basic Policies for Reactor Safety Enhancement (Continued) 2. Adoption of phased approach Select safety measures based on the assumption that possible measures and their required reliabilities are different depending on time to spare Accident Occurrence initial response phase Installed equipment Shift team Action by installed equipment Complexity of accident progression (1) (2) (3) second response phase Portable equipment On-sites team Support from off-site Action by Portable Equipment and Management final response phase Support from off-site Augmented by off-site team [time] Fire engines High pressure injection pump (installed equipment) Power supply cars Tank trucks from off-site 8

10 Basic Policies for Reactor Safety Enhancement (Continued) 3. Ensuring integrity of Containment Vessel in severe accidents Clarify requirements for Containment Vessel and auxiliary equipment after core damage and then implement safety measures Define twice design pressure as upper limit pressure of Containment Define 200 ºC as upper limit temperature of Containment Define function requirements for auxiliary systems in order to contain fission products in Containment as long as possible 9

11 Safety Measures to enhance 1 st Layer of Defense in Depth Measures against tsunami (15m) Sea Wall, Tidal Embankment, Tidal Walls, Boards, Water-tight Doors, etc. 10m 15m above sea Sea Wall Tidal wall Tidal board Water-tight door Measures against Tornado (Fujita Scale 3) Hardened fuel tanks for emergency diesel generators Put N 2 to prevent explosion タンク液面上部の空隙に 窒素を封入することで防爆構造とする Hardened Tank Thickness 32 mm (Originally 9mm) 板厚 40mm * ( 従来 9mm) *: 今後の詳細検討により決定 Measures against External (Forest) Fire Creation of the fireproof belt Fireproof belt Unit 3 Unit 1 Unit 4 Unit 2 Fireproof belt 防火帯 Unit 6 Unit 7 Unit 5 防火帯設置イメージ図 Map of the plant with fireproof belt 10

12 Safety Measures to Enhance 2 nd Layer of Defense in Depth Measures against Tsunami Flooding and Internal Flooding Reduce flooding sources (seismic reinforcement of low class equipment) Waterproof treatments/ flap gates to protect important equipment Install drain pumps for inundation beyond postulated damage Waterproof Filler R/B R/B Stair Case R/B 階段室 Room T/B RW/B Rw/B Stair RW/B Case 階段室 Room T/B Waterproof treatment for piping Waterproof treatment of Upper Hatch 1FL 1FL Waterproof treatment for cables Important Equipment Flap Gate for HVAC ducts Watertight Door B3FL RCIC/RHR(A) Room室 RCIC B3FL MUWC MUWC Room 室 MUWC Funnel with check function 常設排水可搬式排水 Potable Permanent ポンプポンプ Drain Drain Pump Pump R/B : 原子炉建屋 T/B : タービン建屋 RW/B : 廃棄物処理建屋 RCIC : 原子炉隔離時冷却系 RHR : 残留熱除去系 MUWC: 復水補給水系 Permanent 常設排水ポンプ Drain Pump 常設排水 Permanent ポンプ Drain Pump 可搬式排水 Potable ポンプ Drain Pump Measures against internal flooding Installation of Drain Pumps 11

13 Safety Measures to Enhance 2 nd Layer of DiD (continued) Measures for Fire Protection Prevention Fireproof or fire-retardant materials (incombustible cable has been used since construction) Rigid management of combustible materials like lubricant oil Early detection and extinction Diversified fire detection devices Installed fire suppression systems Mitigation Fire Barriers with 3-hour fire resistance capability Fire proof dumpers Fireproof treatment on piping and cable penetrations Cable wrapping Fire Suppression System Cable Wrapping (7 layers) Fireproof Treatment of Cable Penetrations 12

14 Measures to Enhance 3 rd Layer of DiD and Support Systems Water Injection and Heat Removal Functions Enhance High Pressure Injection Function: High Pressure Alternate Cooling System Enhance Depressurization: Back-up Actuation Mechanisms for SRVs Additional Water Source: Reservoir Enhance Heat Removal Function: Alternative Heat Exchange Vehicles HP Injection Enhanced Power Supply of Existing Injection SLC pump RHR pump CRD pump MUWC pump LP Injection Depressurization Fire Engine HPAC Reactor Heat Removal SRVs PCV 1 次格納容器 2 次格納容器 Back-up Battery and Cylinder R/B Additional Water Source K L M E F G N R S T C A B H U P D J C D A B Alternate Heat Exchange Vehicle Reservoir Self-Operated 3-way Valves Nitrogen Cylinders SRV Back-up Actuation Mechanisms 13

15 Safety Measures to Enhance 3 rd Layer of DiD (continued) High Pressure Alternate Cooling System (HPAC) Back-up system of RCIC to enhance reliability of high pressure injection, activated in case of malfunction of RCIC under SBO to prevent core damage Illustration of the system PCV RPV S/C Battery Turbine Power supply from battery on an upper floor Installed at an elevation higher than RCIC from the viewpoint of locational diversity M O RCIC Pump HPAC Turbine Pump R/B MCR HPAC Steam Line HPAC Water Line Control from MCR Remote manual operation is possible from MCR CST Operation could be done by open/close operation of steam inlet valve Use of a steam-driven turbine pump which requires no powered auxiliary system, improving reliability under SBO conditions 14

16 Safety Measures to Enhance 3 rd Layer of DiD (continued) Reactor Alternative Heat Exchange Vehicle Back-up ultimate heat sink for the Reactor in case of LUHS events [Freshwater Pump Specification] Quantity: 1; Flow rate: 420m 3 /h; Pump head: 40m Connection Port Cold shutdown can be achieved within 48 hours. Heat exchanging capacity: 18.6MW Freshwater flow rate: 420m 3 /h Seawater flow rate: 500m 3 /h Freshwater outlet temperature: 32 Seawater intake design temperature: 29 Freshwater pump Hx Hx Reactor Building Alternative Seawater Heat Exchanging System 海水熱交換器建屋 Seawater Heat Exchange Building RHR Hx 原子炉補機冷却海水ポンプ Inundated and cannot be used 電動機 RHR pump Seawater 15

17 Safety Measures to Enhance Support Systems Power Supply Functions Measures for quick power supply Gas-turbine generators and power supply cars on higher ground Emergency switchgears and installed electrical cable Enhancement of reliability of DC Power Additional DC power with a small generator on the top floor of the Reactor Building Additional DC Battery Charge Placed on top floor of Reactor Building Power Supply Car GTG Emergency Switchgear (Placed on higher ground) Safety Area Safety Area Tokyo Electric Power Company Holdings, Inc. All M/C Rights Reserved. M/C 16

18 Safety Measures to Enhance 4 th Layer of Defense in Depth Protection of Containment Vessel and prevention of uncontrolled release Protection of Containment by preventing over-pressure/temperature: Top head flange cooling, increased durability of seal in severe accident environment Mitigation of radioactive material release: Filtered Vent Prevention of hydrogen explosion: Passive Autocatalytic Recombiner Prevention of leakage from primary containment vessel Hydrogen treatment Passive Autocatalytic Recombiner Increased durability of seal material Control over radioactive material release and Discharge of hydrogen Top head flange cooling line Water intake canal Alternative spray means for primary containment vessel The second filtered vent facilities Water injection into lower drywell The first filtered vent facility 17

19 Safety Measures to enhance 4 th Layer of DiD (Continued) Failure of the Containment Vessel at Unit 2 of Fukushima Daiichi NPS Significant leakage occurred at 0.75 MPa and 175 ºC Near the Containment top flange radiation level after the accident was relatively higher than the other areas in the reactor building Top flange gaskets made of silicon rubber must have been degraded in high temperature steam environment, which continued much longer than design basis LOCA conditions 格納容器圧力 (MPa[abs]) D/W 圧力 (MAAP5.01) S/C 圧力 (MAAP5.01) 実測値 (D/W) 実測値 (S/C) トーラス室に浸水した水による S/C の除熱開始 ( 仮定 ) Significant 格納容器漏えい Leakage ( 仮定 ) SRV 開 格納容器温度 ( ) トーラス室に浸水した水による S/C の除熱開始 ( 仮定 ) SRV 開 Significant Leakage 格納容器漏えい ( 仮定 ) 0.2 計装バッテリ枯渇に伴うハンチング S/C 圧力計指示不良 50 D/W(MAAP5.01) S/C( 気相 )(MAAP5.01) S/C( 液相 )(MAAP5.01) S/C( 液相 )(MAAP4) 0.0 3/11 12:00 3/12 0:00 3/12 12:00 3/13 0:00 3/13 12:00 3/14 0:00 3/14 12:00 日時 Pressure and temperature trend of Fukushima Daiichi Unit 2 during the accident 3/15 0:00 Date 3/15 12:00 3/16 0:00 Containment Pressure 3/16 12:00 3/17 0:00 3/17 12:00 3/18 0:00 0 3/11 12:00 3/12 0:00 3/12 12:00 3/13 0:00 3/13 12:00 3/14 0:00 3/14 12:00 日時 Date 3/15 0:00 3/15 12:00 3/16 0:00 Containment Temperature 3/16 12:00 3/17 0:00 3/17 12:00 3/18 0:00 18

20 Safety Measures to Enhance 4 th Layer of DiD (Continued) Reinforcement of Containment robustness in SA environment Buck-up seal Improved EPDM seal Top head side Body side Outside of PCV Increased durability of seal material No. 1 2 Results of improved EPDM seal performance tests Heating condition Dry 200, 168h Steam 1MPa, 250, 168h Flange opening 0.8mm* 0.8mm* 0.3MPa 0.65MPa 0.9MPa No leakage No leakage No leakage No leakage No leakage No leakage * Tests were conducted in ½ scale. A opening of 0.8 mm is equivalent to 1.6 mm in real scale. Water intake canal Alternative spray means for the Containment Vessel Water injection into lower drywell 19

21 Safety Measures to Enhance 4 th Layer of DiD (Continued) Filtered Containment Venting System developed by TEPCO Metal filter 金属フィルタ Organic iodine filters Mixing elements Scrubber Nozzles 気泡細分化装置 ノズル Silver zeolite Decontamination Factors Aerosols: over 1000 Elemental Iodine: over 1000 Organic Iodine: over 50 Aerosol and elemental iodine filter 20

22 Safety Measures to Enhance 4 th Layer of DiD (Continued) ph Control (alkaline control) Inhibit production of iodine gas, and reduce amount of iodine released from the Containment Vessel by making water in the Containment alkaline Containment Vessel Alkaline control Condensate Storage Pool Sodium Hydroxide Solution MUWC pump (Make Up Water Condensate) 21

23 Safety Measures to Enhance 4 th Layer of DiD (Continued) Alternate Recirculation Cooling System(ARCS) developed by TEPCO Containment venting can be avoided by continuous heat removal from suppression chamber Containment spray RHR 1 Containment Vessel alternate Hx External connection port CSP Water injection into reactor MUWC (A) Suppression chamber MUWC (B) MUWC (C) SPCU RHR (B) HPCF (B) Hx (B) 1 Rw/B Alternate circulation cooling system (established part) Alternate circulation cooling system (newly established part) 22

24 Safety Measures to Enhance 4 th Layer of DiD (Continued) Containment Pressure [MPa(gage)] Effectiveness of ARCS ARCS starts PCV pressure limit for severe accident (620kPa) Dry Well Suppression Chamber Pressure suppression by spray Time Containment pressure trend of Kashiwazaki Kariwa Unit 7 in a severe accident with large break LOCA, SBO, and loss of all ECCS 23

25 Challenges in the Process of Safety Enhancement Examples of Additional Measures Required by NRA Measures against Tornado Fujita Scale 3 that has never appeared in the areas facing Japan Sea was required to be applied, and consequently the oil tanks were replaced by new ones with 40mm wall thickness Fire Protection Measures needed to increase the number of fixed fire suppression system (from 20 to 120) due to conservative consideration of the capability of self fire brigade Measure to maintain negative pressure in Reactor Building during severe accident SGTS was required to be activated under SBO condition during severe accident based on conservative assumption of decontamination factor (DF=1) for PCV leakage and ventilation rate (infinite) of Reactor Building Tokyo Electric Power Company, Inc. All Rights 24

26 Lessons Learned Challenges to be Considered How independent external events should be considered during the response period against severe accident, that could be very long How seismic robustness of equipment, that is expected as diversified function, should be required How the reliability of operations in the buildings and in the field should be secured redundancy, diversity, environment, human factor Development of multi-unit PRA method Establishment of organic iodine removal technology More realistic simulation model on how the object could fly in a wind speed field caused by tornado How field walk-down and coordination between works should be made most effectively to optimize the design & layout and minimize the cost Tokyo Electric Power Company, Inc. All Rights 25

27 Organizational and Cultural Challenges in TEPCO Negative linkage of the lack of Safety awareness, Engineering capability and Communication ability went into insufficient readiness for accident. Underestimate external event risk Underestimate severe accident risk Consider capacity factor as an only important performance indicator Not to learn from others experience Safety Awarenes s Lack of daily effort to improve safety Excess costs for SCC and seismic measures for an availability factor Worried plant shutdown because of minor mistakes Explanation is required if we admit it is not safe Overconfidence that safety had been established Desire that it is safe enough Communicatio n Ability Continue risk communicatio n Too much dependence on plant manufacturer Engineering Capability Insufficient inhouse design capability Insufficient ability to understand total system High-cost structure Focused on supervision work Excess dependence on partner companies Avoid direct work by inexperienced personnel Technical Capability Insufficient inhouse direct work capability Ritual emergency training Cannot explain additional measures necessity if it is safe enough Insufficient readiness for accidents 26

28 Nuclear Safety Reform Plan Reflection of Fukushima Nuclear Accident and Nuclear Safety Reform Plan was issued on March 29, It contains six action plans. Governance Action plan 2 Action plan 3 Enhancement of Oversight and Support for Top Management Enhancement of Ability to Propose Defense-in- Depth Measures Safety Awarenes s Action plan 1 Reform from Top Management Engineering Ability Action plan 5 Action plan 6 Reorganization of Emergency Response Organizations Enhancement of Human Development for Improving Nuclear Safety Engineering Ability Communication Ability Action plan 4 Enhancement of Risk Communication Activities Our Determination Improve safety level day by day reflecting the experience of Fukushima Nuclear Accident and be a nuclear operator who can continuously create supreme safety. 27

29 Output Output Output Actions to Improve Issues and Accelerate Reforms Improvement in Governance [Critical success factors for improvement] Good management [Action] Management Model Project Expand the project output to the entire Nuclear Power Division so that tasks are conducted with the same objectives at any level and in any organization. Improvement in Engineering Capability Continuous Strong Leadership [Individual] Systematic Education and Training of Global Standards Management model Fundamentals (Ideal behavior for each business field) Succession plan Job Description Human Resource Database Nuclear Human Resource Development Center World s Best Education and Training Program Personnel with Engineering and Management Capabilities [Organization] Strengthening in-house Engineering Capability Nuclear Engineering Center 28

30 Management Model Vision Mission Sense of values Keep the Fukushima Nuclear Accident firmly in mind; we should be safer today than we were yesterday, and safer tomorrow than today; we call for nuclear power plant operators that keep creating unparalleled safety. Power Generation Division Efficiently generate nuclear power under the world s highest standards of safety / Decommissioning Division Continue to reduce risk and complete decommissioning Uncompromising safety and the pursuit of quality (Safety Awareness) Basic plan for achieving these goals Efficient Operation under the World s Highest Safety Standards Operation and Tasks that directly support Operation Tasks that support Efficient Operation/Management Work Management Equipment Reliability Build trust with stakeholders (ability to promote dialogue) Engage in never-ending reform and improvements Radiation Protection Maintenance Project Management Configuration Management Operation Chemistry Engineering Emergency Response Fire Protection Further foster individual ability and strengthen the organization's ability to learn (Technical Capability) Promote in-house participation where employees see, listen and touch for themselves Radioactive Waste and Environmental Management 運転上の意思決定反応度管理 Quality Assurance Budget Management/Fiscal Assessment Power Generation Division work configuration Tasks that support pre-operation and post-operation Activities to support Reform and Improvement Safety Culture Cultivation Risk Management/PRA Performance Improvements Construction Safety Awareness Nuclear Security/Cyber- Security Occupational Safety Leveraging of Operating Experience Decommissioning External Communication Siting Community PR Cooperation with contractors Communication Capability Fundamentals Internal Communication General Affairs Change management Nuclear Fuel Cycle Human Resource Management Education/Training Procurement Engineering Capability Standards IT/AI Technical Development and Introduction Management Performance Tokyo Electric Management Power Company Holdings, Inc. All Rights Review Reserved. CFAM Monitoring Observation Performance Review Safety Steering Committee Nuclear Risk Management Committee Nuclear Safety Oversight Office Chief Nuclear Engineer Nuclear Safety Review Board Internal Audit Office Nuclear Reform Monitoring Committee Board of Directors 29

31 Emergency Response Capability Restructure of Emergency Response Organization Emergency Response Director Before Information Team Logistics Team 12 teams in parallel Emergency Response Director After (ICS) Public Communication Plant Control Leader Engineering Leader Logistics Leader Safety Supervisor Administration Leader Planning team (unit 1-4) Planning team (unit 5-7) Information team RP team 30

32 Emergency Response Capability (Continued) Training for Emergency Response Comprehensive emergency drills and specific skill trainings have been conducted for 45 times and 7600 times respectively since the accident Night trainings were carried out with temporary lighting (Car headlight, flashlight, balloon light) ERC Rubble removal by wheel loader Gas turbine generator Power supply car Offsite center Firefighting training Alternative heat exchanger Hose Laying Logistics support base Transport of injured person Satellite communications vehicle Transport of N 2 compressed gas cylinder 31

33 Emergency Response Capability (Continued) Offsite Emergency Support Center Sufficient food and fuel are stored on-site to support emergency response (food for 8 days and fuel for 150 days) Making emergency transportation contract with transportation company and giving drivers lectures on radiation. Offsite emergency support centers has been prepared to control entry into affected zone and support materials On-site Emergency Food Image of Offsite Emergency Support Center (Picture of J-Village) 32

34 Emergency Response Capability (Continued) Offsite Emergency Support Center for Enhancement in Logistics Kashiwazaki Kariwa NPS TEPCO Shinanogawa Power Station (23km) Kashiwazaki Energy Hall (8km) Atema Highland Resort (44km) 33

35 Emergency Response Capability (Continued) Nuclear Emergency Assistance Center (J-NEACE) Located in Fukui Prefecture (350km from Kashiwazaki Kariwa NPP) Operated by JAPC (Japan Atomic Power Co.) 20 staff, on-call around the clock, 5 remote-control robots Main missions are: - Emergency transportation of robots - Support of robot operation - Training of emergency response staff of nuclear operators 34

36 Conclusions Our Resolution: We will never forget the Fukushima Nuclear Accident. We will increase the level of safety today more than yesterday and tomorrow more than today, and we will become a nuclear operator that continues to create unparalleled safety. Tokyo Electric Power Company, Inc. All Rights 35

37 Thank you for your attention 36