World Efforts after Fukushima and Lessons Learned from the Accident

Transcription

1 Fukushima 1 World Efforts after Fukushima and Lessons Learned from the Accident Takehiko Saito Federal Authority for Nuclear Regulation, UAE ex- IAEA, ex-nuclear Safety Commission of Japan, and ex-toshiba Corporation World Nuclear University Summer Institute Oxford, England August 1,

2 Outline 1. Fukushima Accident Overview: Uniqueness of the Accident 2. Impact to the World: International Efforts 2.1 Stress Test 2.2 Japanese Efforts 2.3 Efforts of US 2.4 Efforts of Emerging country, UAE 2.5 IAEA Efforts 3. Key Lessons Learned and Discussion 4. Final Remarks 2

3 1. Fukushima Accident Overview: Uniqueness of the Accident - One of the Largest Earthquake in the World - Station Blackout (SBO) and Loss of Ultimate Heat Sink (UHS) for prolonged Time - Multi-Unit Accident 3

4 Three Mile Island Accident Loss of Coolant Accident (LOCA), B&W PWR, USA in 1979 The reactor was severely damaged but radiation was contained and there were no adverse health or environmental consequences. Simple Schematic of the Three Mile Island Unit 2 Nuclear Power Plant. Source: U.S. Nuclear Regulatory Commission Fact Sheet on the Accident at Three Mile Island NRC Image of TMI-2 Core End Stable State. 4

5 Chernobyl Accident Reactivity Accident, RBMK, Ukraine in 1986 The destruction of the reactor by steam explosion and fire killed 31 people and had significant health and environmental consequences. The death toll has since increased to about 56. Source: The Nuclear Energy Agency (NEA)/OECD Chernobyl Disaster Aftermath 5

6 Fukushima Accident SA caused by Extreme External Event (Natural Hazards), BWRs, Japan, March, 2011 The cores of three reactors (Units #1, #2 & #3) were severely damaged due to Station Blackout and Loss of Ultimate Heat Sink caused by Earth Quake and Tsunami (resulted in core melt-down and hydrogen explosion in reactor buildings of Units #1, #3 and #4). Fukushima Daiichi Unit 4 on March 15, 2011 Fukushima Daiichi Unit 1 on March 12, 2011 Source: TEPCO News Source for Media: Photos for Press 6

7 Great Eastern Earthquake: One of the Largest Earthquake in the World 7

8 Source Faults of the Great East Japan Earthquake 8

9 Giant Tsunami Waves after the Earthquake 9

10 Damage by the Earthquake 10

11 Inundated by Huge Tsunami 11

12 Tsunami is the Initiator of the Disaster 12

13 SBO & Loss of UHS for Prolonged Period : Status of Units 1-3 Immediately after Tsunami 13

14 14

15 15

16 Status of Units 1-3 Immediately after Tsunami: UHS and Core Cooling 16

17 Multi-Unit Accident 17

18 18

19 2. Impact to the World: International Efforts Similar to the TMI and Chernobyl accidents, this accident had an effect world-wide. However, unique to this accident, every country with operating nuclear power plants was called upon to respond to their government and citizens to report on the safety of the nuclear reactors in their country in a manner never before experienced. 19

20 2.1 Stress Test 20

21 EU Stress Test 25 March 2011 On 25 March 2011, the Heads of States and Governments of the EU Member States, reunited in the European Council, concluded that the safety of all EU nuclear plants should be reviewed, on the basis of comprehensive and transparent risk and safety assessments. "The European Nuclear Safety Regulators Group (ENSREG) and the Commission are invited to develop as soon as possible the scope and modalities of these tests in a coordinated framework in the light of lessons learned from the accident in Japan and with the full involvement of Member States, making full use of available expertise (notably from the Western European Nuclear Regulators Association). WENRA is a network of Chief Regulators of 16 EU Member States and Switzerland, as well as of other interested European countries which have been granted observer status. 21

22 Objectives of EU Stress Tests The stress tests are defined as a targeted reassessment of the safety margins of nuclear power plants in the light of the events which occurred at Fukushima: extreme events challenging the plant safety functions and leading to a severe accident. This reassessment will consist in a verification of the preventive measures and in an evaluation of the response of a nuclear power plant when facing a set of extreme situations, chosen following a defense-in-depth logic (initiating events, consequential loss of safety functions, severe accident management issues). For a given plant, the reassessment will report on the effectiveness of the preventive measures and on the response of the plant, noting any potential weak point and cliff-edge effect, for each of the considered extreme situations. 22

23 Stress tests specifications Proposal by the WENRA Task Force 21 April

24 24

25 Stress Test Report and additional plant visits agreed 26 April 2012 Adoption of the ENSREG stress test report and the agreement to examine some safety aspects in more detail and prepare a follow up in the next few months. Additional visits of power plants and analysis of some safety aspects in more detail declared. The review concluded that all countries have taken significant steps to improve the safety of their plants. It has also demonstrated the benefit of sharing between national regulators the results of the stress tests and ideas for strengthening safety and robustness of plants. ENSREG and the EU have agreed to continue with safety improvements of nuclear power plants and do a follow up to cover additional safety aspects: Additional visits of nuclear power plants Implementation of the recommendation of the ENSREG report Implementation of the IAEA action plan 25

26 Stress Test in Other countries 26

27 2.2. Japanese Efforts 27

28 NISA Report to IAEA, 4 April 2012 Report of the Japanese Government to the IAEA Ministerial Conference in Nuclear Safety,: The Accident at TEPCO s Fukushima Nuclear Power Station, June 2011 NISA Report to IAEA, September, 2011 NISA Report to IAEA, March 2012, Report of Independent Investigation Committee by Private Sector, 11 March 2012 Report of sub-committee of Technical Analysis, Japan Atomic Energy Society, 9 May 2012 TEPCO s Internal Investigation Committee Report, 20 June, 2012 National Independent Investigation Committee (NAIIC) Report, 5 July 2012 Government Investigation Committee Report, 23 July

29 29

30 30

31 31

32 2.3. Efforts of USA 32

33 33

34 Japan Task Force Report by U.S. NRC Japan Task Force report is available from U.S. Nuclear Regulatory Commission (NRC) website ( 34

35 35

36 36

37 2.4 Efforts of UAE 37

38 38

39 39

40 40

41 41

42 42

43 Technical Assessment: External Events The most significant potential external event challenges are earthquakes, flooding, high temperatures, and sandstorms. These are discussed below, (next slides) including their implications for consequential loss of off-site power supplies and cooling water and for the mitigation of severe accidents at multiple units. 43

44 Earthquakes The design basis earthquake hazard for the Barakah site has been considered in the context of the review of PSAR Chapter 2. The applicant considers the seismic margin for the Barakah facility structures, systems and components to be sufficient given the site specific hazard. However, for extreme events beyond the design basis, the FANR staff concluded that further information is needed with regard to the seismic margin or capacity for the Barakah units. This includes situations where non-seismically designed SSCs could be challenged and have adverse consequences on the operation of structures or equipment that is relied upon for coping with extreme events at the multiple-unit Barakah site. The applicant is performing a seismic Probabilistic Risk Analysis (PRA) as part of the Barakah licensing review, which will address a number of Fukushima-related issues and provide verification that 44 margin exists to accommodate extreme events.

45 45

46 Flooding (1/2) The design basis coastal flooding considered a tsunami originating from the Makran Subduction Zone outside of the Arabian Gulf and a cyclone induced storm surge as major sources of this hazard. A combination of these was also considered in the determination of the final plant grade with the objective of assuring a dry site in relation with the design basis for coastal flooding. Appropriately, the source of the design basis tsunami was chosen to be outside of the Arabian Gulf because there are no sources of tsunamigenic faults within the Arabian Gulf itself. The FANR staff concludes that a further evaluation of a beyond design basis tsunami and the combination of storm surge and tsunami is warranted in order to understand the increase that this could cause in run-up at and inundation of the Barakah site. 46

47 Flooding (2/2) In this context, the applicant will, using appropriately conservative assumptions and a suitable mathematical model, evaluate the flooding caused by a tsunami generated by an earthquake at the Makran subduction zone (outside the Strait of Hormuz) corresponding to a full rupture of this fault. The applicant has proposed design changes, including water-tight doors and relocated penetrations which will provide protection against flooding well above the flooding level that would result from a design basis tsunami. The seismic consequences of such a very large but distant earthquake on the Barakah site ground motion and consequently on the facility will also be documented along with the need for any additional site or facility protection or mitigation upgrades. 47

48 Other External Initiating Events (1/2) The relatively distant location of shipping channels and shallow depths of the Arabian Gulf in the vicinity of the Barakah site provide ample time for plant operators to implement actions to prepare for and mitigate the effects of major oil spills. The applicant s strategy for addressing extreme toxic gas events, detecting gases and isolating the control room, is acceptable. Taking appropriate precautions prior to the onset of sand and dust storms will ensure that the plant and plant operators are properly prepared to deal with the potential effects and minimize the consequences of these events. In the limiting case, plant operators who have been properly trained can ensure that the alternate AC diesel generator is preserved for use following the event. 48

49 Other External Initiating Events (2/2) With respect to high temperatures, even at temperatures of 50 C, the Main Control Room air conditioning system design margins will continue to be maintained. The fire Probabilistic Risk Assessment will include consideration of extreme fire and flood events in order to assess vulnerabilities that may need to be addressed. External explosion hazards were evaluated. An evaluation of margins and a qualitative assessment of the robustness of the building/barriers against explosions will be later provided. 49

50 Consequential Loss of Safety Functions The reference plant has one alternate AC diesel generator (in addition to the emergency diesel generators) for two units. The Barakah design currently proposes one alternate AC generator to be shared among units. FANR has requested the applicant to perform sensitivity analyses with multiple, diverse, alternate AC generators to establish what improvements in risk reduction could be achieved. The applicant has proposed to extend the battery duty life to 16 hours from the design basis value of 8 hours. This provides substantial additional time for operators to take measures to cope with a station blackout condition. The applicant has proposed the addition of cross-tie capabilities to provide AC power for emergency loads from any emergency diesel generator or alternate AC diesel generator on the site, and the capability to connect a mobile diesel generator to each unit. In order to fully assess the effects of sand/dust storms or events on the Ultimate Heat Sink and potential impacts on the various downstream systems being served, further analyses will be performed as part of the detailed design. FANR has requested the applicant to address low power and shutdown events in the applicant s Fukushima Report, including appropriate procedural measures to cope with the effects of extreme events affecting multiple units, at the operating licence stage. 50

51 Severe Accident Mitigation Measures The Barakah Units 1 and 2 design already incorporates plant features designed for coping with severe accidents. Nevertheless, a number of areas to improve the mitigation of severe accidents will be addressed at the operating licence stage, including operator actions to flood the reactor cavity. Backup power for communications systems will be provided from emergency electrical sources. FANR has requested the applicant to perform feasibility studies to determine whether alternate means should be used to mitigate spent fuel heat-up and oxidation in the event of uncovery of the spent fuel assemblies, including spraying of water on top of fuel, and establishing a capability to measure pool water level below the top of the stored fuel. 51

52 Safety Improvements Safety Improvement Category Earthquake Tsunami Fires Station Blackout Severe Accident Procedural Prevention/Mitigation Measures Improving the Seismic Capacity of Main Control Room Display (Seismic Category I Alarm Window for Earthquake) Improving the Seismic Capacity of AAC Diesel Generator Building, AAC DG and Auxiliaries (higher than 0.14g) Installation of Water-proof Doors/Gates for Auxiliary Building, AAC DG Building, ESW Intake Structure and CCW HX Building Preparing Countermeasures for Damage of the Outdoor Tanks Improving Fire Protection Facilities and Response Capability of Plant Firefighting Team Unit Cross Tie Design of EDGs and AAC DG for Emergency Power Supply Installation of Mobile DG Connection on the outside of the Auxiliary Building (location and number of Mobile DG TBD) Extension of Fuel Capacity, of AAC DG Fuel Oil Storage Tank, from 8 hr to 24 hr Division C & D Battery Duty Extension from 8 hr to 16 hr Class 1E Power Backup for Communication System External Water Injection for Steam Generators External Water Injection for Reactor Coolant System External Water Injection for Spent Fuel Pool Installation of Passive Autocatalytic Recombiners in the Spent Fuel Pool Building Spent Fuel Pool Instrumentation Upgrade Toxic Gas Monitor in Main Control Room Development of EOPs, SAMG, EP, training, taking into account Lessons Learned from the Fukushima Accident 52

53 2.5 Efforts of IAEA 53

54 54

55 IAEA Fact Finding Mission 55

56 56

57 57

58 58

59 59

60 60

61 61

62 62

63 63

64 IAEA Action Plan in Nuclear Safety, 5 Sep. 2011

65 65

66 66

67 67

68 68

69 69

70 70

71 71

72 72

73 73

74 74

75 75

76 76

77 77

78 78

79 79

80 80

81 Convention on Nuclear Safety (CNS) CNS are held at regular three-year intervals : #1 1999, #2 2002, #3 2005, #4 2008, # On 4 April 2011, the 72 countries that are "Contracting Parties" to the Convention on Nuclear Safety (CNS), which meet every three years to consider the CNS' implementation, gathered at the IAEA's headquarters in Vienna for their fifth Review Meeting. The ten-day Conference, convening from 4 to 14 April 2011, discusses the country reports on nuclear safety that every Contracting Party is obliged to submit. All countries with operating nuclear power plants are among the CNS' Contracting Parties. Extraordinary CNS meeting at the end of Aug

82 Fukushima Ministerial Meeting on Nuclear Safety 82

83 3. Key Lessons Learned and Discussion 83

84 Design on extreme external events (hazards) Designers, operators and regulators need to make a grater effort to understand the severity of external hazards and combinations of hazards. External hazards can create a common challenge to any plant, especially when they have been operating for a significant number of years. Changing environmental conditions can create unexpected natural external hazards. On the other hands, external events can challenge differently plant by plant (site by site) even plant design is the same. External hazards should be treated as mainstream nuclear safety. 84

85 Evaluation of External Natural Events Earthquakes Surface faulting Tornadoes Tropical cyclones Sand and Dust Storm Floods due to precipitation and other causes Water waves induced by earth quakes (Tsunami) Floods and waves caused by failure of structures Slope instability Site surface collapse, subsidence or uplift Soil liquefaction Other extreme natural conditions volcanism, strong winds, sand storms, etc. 85

86 Evaluation of External Human Induced Events Aircraft crashes Chemical explosions Other important human induced events Facilities that sore, process, transport and handle - toxic, - corrosive - radioactive material 86

87 87

88 Tsunami A large safety margin needs be added for tsunami run up for NPP sites because of various uncertainties. Location of essential safety systems should be determeined considering extreme Tsunami/Flood. Leak tightness and water resistance should be assured through comprehensive evaluation of all potential water ways. The methods for hazard estimation and protection of the plant need to be compatible with the advances in research and development. 88

89 Redundancy and Diversity in design of safety systems and components All levels of DiD challenged at the same time concept of redundancy, diversity and physical separation need to include external hazards. 5&6 Redundancy and Diversity of emergency power systems One air-cooled DG saved 1F 5&6 redundancy and diversity of emergency power supply are important (i.e. air-cooled DG and watercooled DG; diesel generator and gas turbine generator). 89

90 Plant capability against SBO and loss of UHS Highly reliable assurance of three cooling functions (Core, CV, SFP) including enabling systems (power/air/water source) such as backup air supply to SRV A needed. Significance of passive safety systems recognized. 90

91 AP1000 Passive containment cooling system Source: IAEA TECDOC 1391 Status of advanced light water reactor designs

92 AP1000 Configuration to Promote IVR of Molten Core Debris Source: IAEA TECDOC 1391 Status of advanced light water reactor designs

93 ESBWR reactor building arrangement Source: IAEA TECDOC 1391 Status of advanced light water reactor designs

94 Passive Melting Core Cooling and Containment Cooling: EU-ABWR CCCS; Corium & Containment Cooling system Heat Removal by PCCS IC/PCCS Hx Cooling Water Tank PCCS Hx Gas Vent Line Condensate Drain Line Steam Suction Line Melting Core Cooling by flooding 下部ドライウェル Driving force of Gas Vent Core Catcher Fusible Valve Source: IAEA Workshop 2011: Toshiba ABWR Technology by Toshiba

95 Emergency Management at TEPCO Under conditions of loss of communication tool and plant information Damage to social infrastructure by earthquake hampered dissemination of information to local government and residents Offsite center: function was lost by loss of electricity and radiation Who is in charge? : PM office, Regulatory body s ERC, Offsite center TEPCO s head quarter, TEPCO s site office (GCI interim report) Lack of Information sharing with local residents on dispersion of FP (SPEEDI) and risk of radiation with neighboring countries on release of slightly contaminated water Data but not information Effective channeling of emergency supports Systematize domestic/foreign helping hands for logistics/experts Needs to revisit Delineation of responsibility, command line, coordination, function of offsite center Communication system Mobile equipment 95

96 Experience Feedback (lessons learned) Lessons learned from the Kashiwazaki-Kariwa experience provided extremely valuable improvements to the emergency response at all the plants. - The so called seismically isolated building (which is also has charcoal filtered ventilation, shielded and located at a high elevation) provided a safe haven to all plant personnel during this disaster and expedited emergency and recovery actions. - The on site fire brigade was also extremely valuable even though there was no fire at the sites. The fire engines were used for injecting water to various structures to provide cooling. - The re-location of the piping for the fire fighting system, on the other hand, turned out to be a mistake for the particular hazard scenario (tsunami). The fact that there was no fire at the F2 plant meant that there was no need for this system. Otherwise the onsite fire brigade which had little hands on experience could have been stretched to cope with multi-tasking (i.e. dealing with fires and providing water injection to various structures). 96

97 A. Lessons Learned in Japanese Government Report to IAEA, September Lessons in 5 specific areas: 1. Prevention of Severe Accident, 2. Severe Accident Management (SAM), 3. Emergency response, 4. Safety infrastructure, 5. Safety culture and implementation status Key points: 1. Design considerations against natural hazards 2. Design considerations against SBO (Station Blackout) and Isolation from UHS (Ultimate Heat Sink) 3. Completeness/effectiveness of SAM 4. Emergency Management 5. Safety regulation and safety culture 6. Multiple unit installation 7. Spent Fuel Pool design 8. International aspects 97

98 B. Lessons Learned in the Report of sub-committee of Technical Analysis, Japan Atomic Energy Society, 9 May 2012 Lessons in 12 specific areas: 1. Seismic motion, 2. Tsunami, 3. SBO, 4. Total loss of core cooling system, 5. Severe Accident Management, 6. Hydrogen explosion, 7. Spent fuel pool 8. Promotion of safety research 9. Safety Regulation and safety design 10. Organization and crisis management 11. Information disclosure 12. Safety management under emergency condition 98

99 4. Closing Remarks After studying Fukushima Accident and subsequent efforts to further improve nuclear safety, the followings are believed to be very important: 1. Close international cooperation of nuclear regulators and industries. 2. Effective use of NPP operating experiences including lessons learned from Fukushima. - OPEX (Operating Experience feedback) - No two NPPs are exactly same (Site unique evaluation) 3. Constant vigilance and improvement!!! - Complacency can kill! 99

100 Thank you for your attention! 100