Comprehensive Safety Assessment for Kashiwazaki Kariwa NPS

Transcription

1 Comprehensive Safety Assessment for Kashiwazaki Kariwa NPS International Experts Meeting on Reactor and Spent Fuel Safety in the Light of the Accident at the Fukushima Daiichi Nuclear Power Plant IAEA, Vienna Mar , 2012 Hideki Masui Seismic Research Manager Tokyo Electric Power Company

2 Contents 1. Background and Concept of Comprehensive Safety Assessment 2. Methodology and Result of Assessment 3. Further Additional Safety Measures in Light of Fukushima Daiichi Accident 4. Continuous Improvement 2

3 1. Background and Concept of Comprehensive Safety Assessment 3

4 Background Date Event Mar Jul.6, 2011 Jul.11, 2011 Jul.22, 2011 Jan Jan.23-31, 2012 Mar.12, 2012 Fukushima Daiichi Accident Chair of NSC issued request to Minister of Economy Trade and Industry for comprehensive safety assessment (stress test) Minister of Economy Trade and Industry and other two Ministers laid out a plan for assessment NISA issued direction to utilities for implementing comprehensive safety assessment Reports of Primary Assessment of Kashiwazaki Kariwa 1/7 were submitted to NISA IAEA mission visited NISA to review NISA s approach to assessment Reports of KK 1/7 were re-submitted to NISA after correction of editorial errors 4

5 Objectives of Stress Test To identify and improve potential vulnerabilities of plant by clarifying quantitative safety margins To secure assurance and trust of general public and local residents 5

6 Two-Step Approach for Stress Test Target Method Event Facility Primary Assessment Plants ready to start-up after outage Conservative approach Earthquake, Tsunami Combination of quake and tsunami SBO, LUHS, SAM Reactor, SFP Scope of this presentation Secondary Assessment All operating plant Realistic approach Same as primary Combination of SBO and LUHS (Other events may be considered) Reactor, SFP 6

7 Primary and Secondary Assessment Material strength confirmed by testing etc. Total Safety Margin Allowable stress limits in code and standard ( d) Calculated stress for design base earthquake ( c) Primary Secondary Seismic margin for primary assessment = d/ c 7

8 TEPCO Nuclear Power Stations Kashiwazaki Kariwa NPS 8212MWe Kashiwazaki Kariwa NPS 8212MWe Fukushima Daiichi NPS 4696MWe Fukushima Daiichi NPS 4696MWe Fukushima Daini NPS 4400MWe Fukushima Daini NPS 4400MWe 8

9 Outline of Kashiwazaki Kariwa NPS Overview of Kashiwazaki-kariwa kariwa NPS The world s largest nuclear power station with capacity of 8,212 MWe 5 units of Boiling Water Reactors (BWR with 1100 MWe -units 1 to 5) and 2 units of Advanced BWRs (ABWR with 1356 MWe -units 6 and 7) 4 units have been back online after NCO earthquake in

10 Safety Measures Implemented After Fukushima Daiichi Accident (Effectiveness of those measures will be clarified in assessment) 10

11 Tide Plate for Reactor Building Tide plate has been installed to R/B to tolerate tsunami up to 15m Before After Ventilation Ventilation Tide Barrier Tide Plate Water Tight Door Ventilation Tide Plate Ventilation Sealed 11

12 Waterproof Work Water-tight door Sealing Material Water-tight door Sealed penetration outer inner 12

13 Emergency Equipment on Site Power Supply Car (14 on site) Portable Generator (20 on site) Fire Engine (8 on site) Wheel Loader 13

14 Emergency High Voltage Switchgear Emergency metal-clad switchgear has been constructed in high ground to distribute emergency power Gas Turbine Power Supply Car 4500kVA R/B Hx/B T/B 500kV Power Supply Car 27m 14

15 Diversified Low Pressure Injection Filtrate water D/D FP MUWC Fire truck R/B D/D FP PCV Sea water C/B RHR (LPCI) RPV In case of inoperable ECCS, 3 systems (MUWC, FP, Fire engine) are available for low pressure injection 15

16 Mobile Heat Exchanger Heat Exchanger Pump pump R/B Hx/B Hx Seawater Pump RHR pump RCW pump RCW Hx 16

17 Reliable PCV Venting PCV venting can be conducted more readily upon SBO by installing backup gas cylinder and modifying AOV Operate MCR PLANT Vital power R/B AO Rupture disk Stack PLANT Vital power AO D/W vent spare Cylinder Valve has been modified to allow manual operation S/C vent spare Cylinder 17

18 Diversified SFP Injection D/D FP pump injection Fire truck(fp pipe) Fire truck(hose) Filtrate water Fire hydrant Hose SFP pool R/B D/D FP pump Joint Fire truck MUWC FPMUW C/B FP pump and fire engine (via FP line or direct injection) are available for water injection to SFP 18

19 Diversified SFP Cooling R/B SFP pool Power supply car T/B Joint FPC H/x Hx/B Unusable due to flooding FPC Submersible pump In case that mobile heat exchange is inoperable, submersible pump connected to existing system can remove heat from SFP 19

20 Methodology and Result of Assessment 20

21 Flow of Stress Test (Primary Assessment) Screening of Initiating Event LOOP, SBO, Loss of RCW, Loss of DC power, ATWS, Loss of I/C, PCV/RPV Damage, R/B Damage, LOCA, Other transients Selection of Safety SSC Safety-related SSCs are selected Assessment of Safety Margin Safety margins of SSCs are estimated Identification of Cliff Edge Assessment of Effect of Safety Measures Cliff Edge (failure path with smallest safety margin) is identified by using event tree and fault tree Effect of implemented Success path with largest safety margin (Cliff Edge) is identified by using event tree and fault tree 21

22 Screening of Initiating Events (KK7,Reactor) Earthquake Initiating Event with Smallest Seismic Margin LOOP (<1.0) SBO Loss of RCW Loss of DC power (2.27) Loss of I/C(1.70) Yes 1.55 Yes LOCA Yes Support System No 1.69 Yes SCRAM No Other transient ATWS (core damage) Detailed Assessment by ET 2.90 R/B Yes 1.47 PCV RPV No No Mitigation function is not expected Mitigation function is not expected LOCA (core damage) RPV Damage (core damage) PCV Damage (core damage) No Mitigation function is not expected R/B Damage (core damage) 22

23 Assessment by ET (KK7,Earthquake,Reactor) Quake Rx pressure Heat Sink DC power HP injection Depressurization LP injection Rx Heat Removal PCV Heat Removal 1.81 Yes 1.52 Yes 1.37 Yes 1.85 LOOP SRV RCW EDG HP Injection HPCS RCIC Yes Seismic Safety Margin before safety measures RHR (SHC) Yes 1.37 Cold Shutdown No Core Damage No LUHS next page SBO next page No 1.81 Yes 1.60 SRV RHR (LPCI) No Core Damage Yes No Core Damage No 1.60 RHR (S/C cooling) No 1.58 PCV venting Yes 1.37 Hot Shutdown 1.37 Hot Shutdown Existing Safety Function Additional Safety Function Scenario before safety measures Scenario after safety measures No Core Damage 23

24 Assessment by ET (KK7,Earthquake,Reactor) LUHS previous page SBO previous page HP injection 1.85 RCIC AC Power Depressurization Yes ( ) Yes 1.81 Yes 1.02 Emergency Switchgear No Core Damage Existing Safety Function Additional Safety Function Scenario before safety measures Scenario after safety measures SRV (Gas Cylind er) No 2.00 or more Power Supply Car No Alternative Injection MUW FP(D/DFP) Yes 1.81 No Core Damage RHR (LPCI) Mobile Hx SRV LP injection Yes No Rx Heat Removal ( ) RHR (SHC) Mobile Hx Fire Engine Seismic Safety Margin after safety measures (1.58) Yes 1.02 Alternative Injection MUW FP(D/DFP) No ( ) No Yes No ( ) Fire Engine PCV Heat Removal ( ) RHR (S/C cooling) Yes 1.58 PCV venting No Yes Yes No Core Damage 1.58 PCV Venting Yes No Core Damage ( ) Cold Shutdown ( ) Hot Shutdown ( ) Hot Shutdown 1.58 Hot Shutdown 24

25 Example of Mitigation Function Assessment Seismic Safety Margin: 1.58 This margin is reflected on ET PCV Venting Failure or 1.58 Atmospheric Control SGTS Piping Failure Piping Failure or or Piping Support Valve Piping Support Valve

26 Screening of Initiating Events (KK7,Reactor) Earthquake LOOP (<1.0) LOPA Loss of RCW Loss of DC power (2.27) Loss of I/C(1.70) Yes Yes 1.69 SCRAM No Other transient ATWS (core damage) Before safety measures: 1.37 After safety measures : 1.58 Cliff edge after safety measure (RPV anchor volt damage) 2.90 R/B Yes 1.47 Yes PCV RPV No 1.55 Yes LOCA No Support System No Mitigation function is not expected Mitigation function is not expected Detailed Assessment by ET LOCA (core damage) RPV Damage (core damage) PCV Damage (core damage) No Mitigation function is not expected R/B Damage (core damage) 26

27 Result of Stress Test (KK7, Earthquake) Before implemented measure After implemented measure Reactor SFP DBEGM=1209 gal 1.37 (Loss of EDG) 1.47 (RPV anchor volt damage) 1.37 (Loss of EDG) 1.37 (Loss of EDG) DBEGM: Design Basis Earthquake Ground Motion Reactor: Due to implemented safety measure (power supply car etc), cliff edge will shift from LOOP to RPV damage SFP: EDG failure can be covered by power supply car. However, margin of EDG is larger than that of MUW (alternative SFP injection). Thereby, cliff edge stay unchanged. 27

28 Result of Stress Test (KK1, Earthquake) Before implemented measure After implemented measure Reactor SFP DBEGM=2300 gal (Loss of RCW) (PCV stabilizer damage) 1.29 (PCV stabilizer damage) 1.45 (R/B overhead crane damage) DBEGM: Design Basis Earthquake Ground Motion Reactor: For initiating event PCV damage, no mitigation function is expected for primary assessment. Therefore, cliff edge stay unchanged SFP: Due to implemented safety measure (power supply car etc), cliff edge will shift from Loss of RCW to R/B overhead crane damage 28

29 Result of Stress Test (KK1/7, Tsunami) Design Tsunami Height 3.3m KK1 (Reactor, SFP) 15m 5m KK7 (Reactor, SFP) 15m 12m Margin Margin 11.7m 11.7m 3.3m Before After Before After Before implementation of safety measure: Allowable tsunami height is conservatively estimated to be equal to site height. After implementation of safety measure: Allowable tsunami height is the one under the assumption of which water seal measures were conducted. 29

30 Combination of Earthquake and Tsunami (KK7) Seismic Margin Secondary Assessment Expanded Safety Margin Secondary Assessment 0 3.3m Design Tsunami Height 12.0m Site Height 15.0m Allowable Tsunami height Safety margin was expanded due to implementation of safety measures 30

31 Assessment for SBO and LUHS Tolerance time is estimated after SBO or LUHS Tolerance time is determined by whichever shorter of the followings - Water supply time - Power supply time Conservative conditions are assumed: - All 7 reactors and SFPs become SBO or LUHS - No support is expected from outside 31

32 Result of Stress Test (SBO, KK7, Reactor in Operation) Reactor + SFP Before Water Power Time CSP 10h Battery 16h(Actual Life, 8h on design basis) About 10 hours CSP 0.7d (Minimum water level was changed) Due to concern of salt damage, 7 days was assumed. After Water Power Fresh water 4.9d Sea water 7d Battery 16h Power supply car 94d Determined by capacity of fuel Time About 12 days 32

33 Result of Stress Test (SBO, KK7, Reactor Shutdown) SFP Before Water Power Time Before safety measures, there was no specific procedures to inject water after SBO About 5 hours (Time to water temperature reaches 100 ) CSP 0.9d Due to concern of salt damage, 7 days was assumed. Water Fresh water 5d Sea water 7d After Power Power supply car 99d Time About 12 days 33

34 Result of Stress Test (LUHS, KK7 Reactor/ SFP) 196 days Determined by capacity of on-site fuel storage for power supply car Determined by capacity of CSP and purified water tank Mobile Heat Exchanger 1 day Power Supply Car Before After 34

35 Summary of Stress Test Result KK 1/7 have sufficient robustness against events beyond design basis through additional safety measures implemented after Fukushima Daiichi Accident In near future, secondary assessment will be conducted to identify and address potential vulnerabilities of plant. 35

36 Further Additional Safety Measures in light of Fukushima Daiichi Accident 36

37 Course of Event and Countermeasures <Event> <Countermeasure> Tsunami Inundation of building SBO LUHS Core damage Hydrogen explosion Radiation Release Protection from tsunami Prevention of core damage upon Loss of AC/DC,LUHS Mitigation upon core damage Support for emergency response Tsunami barrier Tide barrier Water proof sealing Backup power Heat removal Diversified injection Roof venting Reliable PCV venting Communication Radiation Protection Training 37

38 (1)Protection from Tsunami 38

39 Tsunami Barrier for Entire Site Tsunami Barrier to prevent or deter the force of tsunami T.P.+15 T.P T.P.+12 T.P Cement-Soil Mixture Mound (Unit 5-7) Reinforced Concrete Wall (Unit 1-4 ) 39

40 (2) Prevention of core damage upon Loss of AC/DC Power, LUHS 40

41 DC Power Life Extension Battery(1H) 500Ah DC 125V Main Line(1A) DC 125V Main Line(1H) Backup Battery DC 12V 166Ah 40set=6640Ah DC 125V Main Line(1B) By cross-tying of existing batteries and addition of backup battery, battery life for RCIC will be extended from 8 to 72 hours 41

42 Diversified High Pressure Injection Fire hose Hydrant Sea Water FP M M SLC MUWC D/D FP Filtration water Tank M M MUWP(B) Pure Water Tank RCIC Tb RPV PCV CRD 3 systems (RCIC, SLC, CRD) are available for high pressure injection RCIC CRD SLC 42

43 Diversified High Pressure Injection Diversified Injection Method Power Supply Injection RCIC SLC CRD Diversified Power Supply Gas Turbine Gen. (Emergency M/C) Power Supply Car (Switchboard) Power Supply Car (Direct Connection to Motor) Battery Manual startup 43

44 Depressurization by Safety Relief Valve Temporary Switch SRV NO Battery RPV Nitrogen cylinder Backup cylinder PCV Nitrogen supply equipment Backup gas cylinder and battery are prepared to facilitate SRV operation upon SBO 44

45 Construction of Reservoir Reservoir is under construction on high grounds with capacity of 18,000m 3 45

46 Effect of Reservoir CSP 0.7d Reservoir Water Power Fresh water 4.9d Fresh water 7d Battery 16h Power supply car 94d Sea water 7d Time About 19 days Reservoir will extend SBO tolerance by 7 days (from 12 days to 19 days) 46

47 Underground Fuel Tank Underground fuel tanks are under construction to extend life of gas turbine generator Tank truck Gas turbine generator car High voltage distribution board for emergency Underground diesel fuel tank Underground diesel fuel tank Capacity: 150m 3 Location: 35m above sea level R/B High voltage distribution board for emergency 47

48 (3) Mitigation upon Core Damage 48

49 Roof Vent of Reactor Building To facilitate hydrogen ventilation, roof vent has been installed at KK unit 1 and 7. Roof Vent R/B Wire 49

50 Diversified PCV Cooling D/W spray R/B joint FP-MUWC line Fire truck S/C spray sea To mitigate overpressure and over temperature of PCV, PCV spray will be conducted by use of freshwater or sea water. 50

51 Filtered Containment Venting System Filtered containment venting system will be introduced to minimize radiation release after core damage. Design is now under consideration. SFP Mist Separator Water (Image taken from NISA s Advisor s meeting Dec.27, 2011) Image of FCVS 51

52 (4)Enhanced Support for Emergency Response 52

53 On-site Emergency Response Center Designed based on experience of quake hitting Kashiwazaki Kariwa in 2007 Built with Base Isolated Structure. Equipped with communication devices, teleconference system, etc. Base Isolated Structure Laminated Rubber Movable Bearing 53

54 Communication Device and Network In addition to existing diversified communication devices, new network line and some devices were prepared Batteries can be recharged by power supply car. Battery life was extended Battery Life (2 8hrs) 6 New Lines Battery Life (3 8hrs) Walkie-Talkie(9 30) Satellite phone(5 7) Power Supply Car(0 14) 54

55 Radiation Protection Equipment Shielding vests (with tungsten) are prepared Dosimeters and face mask are stored at ERC Equipments for RP can be shared among nuclear licensees upon emergency Shielding vests image weight : about 18 kg shielding ability lead 2mm Dosimeter face mask (shared among nuclear licensees ) 55

56 Training for Emergency Response 5 comprehensive trainings have been conducted so far after Fukushima Daiichi Accident 4 daytime training and 1 night training. Night training was carried out with temporary lighting (Car headlight, flashlight, balloon light) ERC fire engine Power Supply Car wheel loader Cable Laying Power Supply Car Connection of FP-line Balloon light 56

57 Development of New Procedures Outline Contents Tsunami SAMG Severe Accident Management Guideline for Tsunami Securing power source Extension of RCIC life Injection by FP system Seawater injection by fire engine Operation of roof vent EDMG Extensive Damage Mitigation Guideline Responses against unforeseeable cause-free events RCIC manual startup SRV operation by battery Injection by FP system Manual operation of venting valve To make improvised action more organized one, 2 new procedures have been developed 57

58 Continuous Improvement 58

59 Continuous Improvement From Fukushima Daiichi Accident, we have learned a lot of lessons. Based upon these lessons, we have been implementing additional safety measures. We are committed to continuously improve safety of our plants through collecting new findings domestically and internationally. Followings are some examples of initiatives to improve safety. 59

60 Enhanced Reliability for HP Injection Valves of IC are of failure-close design (Power loss of piping rupture detection circuit closes corresponding isolation valve) Approaches to enhanced reliability for HP injection are considered Isolation Condenser MO MO MO MO MO MO MO MO RPV PLR MSIV FP MUW MO MO PCV 60

61 Enhanced Reliability for PCV Venting Necessity of rupture disk? Bypass line to control release timing? MO Main Stack AO Failure close or open? Necessity of those valves? Relocation for less exposure? IA Solenoid Valve AO AO IA Solenoid Valve AO 61

62 Other Issues for Improving Safety Development of instrumentation resistant to severe accident condition Diversification of cooling function without AC power Reorganization of emergency response and operation staffing to deal with prolonged accident Establishment of transportation base for emergency material and staffing near plant 62

63 Concluding Remarks We are committed to improve the safety of the nuclear power plant through comprehensive safety assessment (Stress Test) and lessons learned from Fukushima Daiichi Accident. For TEPCO, stress test is an opportunity to identify and address weakness of plants. We are going to keep you informed of any update in our English website. x-e.html 63