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Nuclear administration after the nuclear accident in Japan March , 2013 Kenkichi HIROSE
Contents 1. Occurrence of the nuclear accident 2. Significant administrative points learned from the accident at the Fukushima Dai-ichi Nuclear Power Station 3. New framework of nuclear administration 4. Situation of nuclear liability 5. Reinforcement of safety of nuclear power plants (reference ) Electricity production in Japan
1. Occurrence of the nuclear accident 2
Six BWR type nuclear power plants at Fukushima Dai-ichi NPS started operation in the 1970 s. Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Electric output(MWe) 460 784 784 1100 Commercial operation 1971/3 1974/7 1976/3 1978/10 1978/4 1979/10 Reactor model BWR 3 BWR 4 PCV model Number of fuel assemblies in the core BWR 5 Mark-1 400 548 Mark-2 548 548 764 Four BWR type nuclear power plants at Fukushima Dai-ni NPS started operation in the 1980 s. Unit 1 Unit 2 Unit 3 Unit 4 Electric output(MWe) 1100 Commercial operation 1982/4 1984/2 1985/6 1987/8 Reactor model PCV model Number of fuel assemblies in the core BWR 5 Mark-2 764 Mark-2 Advance 764 764 3
Unit 1 ～ 5 at Fukushima Dai-ich NPS has flasktype primary containment vessel (PCV) (source : TEPCO) 4
Before the earthquake and tsunami 3 plants were under operation, and 3 plants were under periodic inspection at the Fukushima Dai-ichi Nuclear Power Station. p Under operation • Unit 1 • Unit ２ • Unit ３ p Under periodic inspection • Unit 4 ( all the fuel were removed from the reactor to the spent fuel pool) • Unit５ • Unit６ 5
Epicenter of Tohoku District - off the Pacific Ocean Earthquake was approximately 130 km off the coast of Sanriku. l. Occurrence: 14: 46 March 11, 2011 l. Mw(moment magnitude): 9. 0 l. Epicenter: approximately 130 km off the coast of Sanriku (at 38. 10 degrees north latitude, 142. 86 degrees east longitude and 23. 7 km deep) Map of JMA seismic intensities observed during the main shock. 6
Loss of cooling capability caused core melt at Unit 1, Unit 2 and Unit 3. Shutdown of reactors and loss of external power supply due to earthquake Start-up of emergency power generators All emergency diesel generators stopped except for one generator in Unit 6 due to tsunami (11 emergency diesel power generator stopped, and one generator(with air cooling)survived. ) Loss of all AC power supply except for Unit 6 (Unit 5 took power supply from Unit 6 on 13 March). Core cooling system not using AC power (Unit 1: IC(isolation condenser), Unit 2 (RCIC(reactor core isolation cooling system), Unit 3: RCIC and HPCI (high pressure core injection system) Stop of core cooling system not using AC power Water injection from a fire extinguishing line (Unit 1: pure water->sea water, Unit 2: sea water Unit 3: pure water-> sea water) During this time without cooling, the fuel was exposed and core melt started, generating hydrogen 7
Water was injected into the reactors via fire extinguishing line using fire trucks as accident management. (source : TEPCO)
Water was injected into the spent fuel pool at Unit 4 by concrete pump car. (source: TEPCO) 9
Hydrogen explosion occurred at the upper part of reactor building at Unit 1, Unit 3 and Unit 4. (source : TEPCO) Total view Unit 4 Unit 1 Unit 3 Unit 2 10
Dose rates measured by monitoring car at the site showed the high level of March 15. 11
Measurement of airborne concentration showed steady decline of release from March to August 2011. 12
Radioactive materials were accumulated in the north-east direction due to the winds of days of release of them. (source : airborne monitoring by MEXT and DOE) as of July 2, 2011 13
Two stages of evacuation areas were set from March to April 2011. (As of August 3, 2011) 14
2. Significant administrative points learned from the accident at the Fukushima Dai-ichi Nuclear Power Station
(1)Training responding to severe accidents should be enhanced. (No. 1) p Conclusion Ø Effective training to respond to accident restoration at nuclear power plants and adequately work and communicate with relevant organizations in the wake of severe accidents was not sufficiently implemented up to now. For example, it took time to establish communication between the emergency office inside the power station, the Nuclear Emergency Response Headquarters and the Local Headquarters and also to build a collaborative structure with the Self-Defense Forces, the Police, Fire Authorities and other organizations which played important roles in responding to the accident. Adequate training could have prevented these problems.
(1)Training responding to severe accidents should be enhanced. (No. 2) p Lessons learned Ø Reflecting on the above issues, we enhance training to respond to severe accidents by promptly building a structure for responding to accident restoration, identifying situations within and outside power plants, facilitating the gathering of human resources needed for securing the safety of residents and collaborating effectively with relevant organizations.
(2)Central control of emergency supplies and equipment and setting up rescue teams should be established. (No. 1) p Conclusion Ø Logistic support has been provided diligently by those responding to the accident and supporting affected people with supplies and equipment gathered mainly at J Village. However, because of the damage from the earthquake and tsunami in the surrounding areas shortly after the accident, we could not promptly or sufficiently mobilize rescue teams to help provide emergency supplies and equipment or support accident control activities. This is why the on-site accident response did not sufficiently function.
(2)Central control of emergency supplies and equipment and setting up rescue teams should be established. (No. 2) p Lessons learned Ø Reflecting on the above issues, we introduce systems for centrally controlling emergency supplies and equipment and setting up rescue teams for operating such systems in order to provide emergency support smoothly even under harsh circumstances.
(3)Responses to combined emergencies of both large-scale natural disasters and prolonged nuclear accident needs to be reinforced. (No. 1) p Conclusion Ø There was tremendous difficulty in communication and telecommunications, mobilizing human resources, and procuring supplies among other areas when addressing the nuclear accident that coincided with a massive natural disaster. As the nuclear accident has been prolonged, some measures such as the evacuation of residents, which was originally assumed to be a shortterm measure, have been forced to be extended.
(3)Responses to combined emergencies of both large-scale natural disasters and prolonged nuclear accident needs to be reinforced. (No. 2) p Lessons learned Ø Reflecting on the above issues, we prepare the structures and environments where appropriate communication tools and devices and channels to procure supplies and equipment be ensured in the case of concurrent emergencies of both a massive natural disaster and a prolonged nuclear accident. Also, assuming a prolonged nuclear accident, we enhance emergency response preparedness including effective mobilization plans to gather human resources in various fields who are involved with accident response and support for affected persons.
(4)A clear division of labor between relevant central and local organizations should be established. (No. 1) p Conclusion Ø Communication between local and central offices, as well as with other organizations, was not achieved to a sufficient degree, due to the lack of communication tools immediately after the accident and also due to the fact that the roles and responsibilities of each side were not clearly defined. Specifically, responsibility and authority were not clearly defined in the relationship between the NERHQs Nuclear Emergency Response Headquarters and Local NERHQs Headquarters, between the Government and TEPCO, between the Head Office of TEPCO and the NPS on site, or among the relevant organizations in the Government. Especially, communication was not sufficient between the government and the main office of TEPCO as the accident initially began to unfold.
(4)A clear division of labor between relevant central and local organizations should be established. (No. 2) p Lessons learned Ø Reflecting on the above issues, we review and define roles and responsibilities of relevant organizations including the NERHQs, clearly specify roles, responsibilities and tools for communication while also improving institutional mechanisms.
“Nuclear Emergency Response Headquarters” was responsible for nuclear emergency including the instruction of evacuation. (Law Cabinet Decisions) Nuclear Emergency Response Headquarters Chief: Prime Minister Cabinet Office Local Nuclear Emergency Response HQs (Inside Prefectural Office of Fukushima) Government - TEPCO Integrated Response Office (including assistance from overseas) Team in charge of Assisting the Lives of Victims around the Nuclear Power Plant Cabinet Office Liaison Meetings among relevant ministries and agencies Team in charge of Responding to the Economic Impact caused by the Nuclear Power Station Incident (review meetings of ministerial Cabinet Secretariat level if necessary) 24
Off-site center near the site was given up due to high-level radiation. (source : Agency of Natural Resources and Energy) 25
(5)Communication relevant to the accident should be enhanced. (No. 1) p Conclusion Ø Communication to residents in the surrounding area was difficult because communication tools were damaged by the large-scale earthquake. The subsequent information to residents in the surrounding area and local governments was not always provided in a timely manner. The impact of radioactive materials on health and the radiological protection guidelines of the ICRP, which are the most important information for residents in the surrounding area and others, were not sufficiently explained. Japan focused mainly on making accurate facts publicly available to its citizens and has not sufficiently presented future outlooks on risk factors, which sometimes gave rise to concerns about future prospects.
(5)Communication relevant to the accident should be enhanced. (No. 2) p Lessons learned Ø Reflecting on the above issues, we will reinforce the adequate provision of information on the accident status and response, along with appropriate explanations of the effects of radiation to the residents in the vicinity. Also, we keep in mind having the future outlook on risk factors included in the information delivered while incidents are still ongoing.
(6)Clear definition of widespread evacuation areas and radiological protection guidelines in nuclear emergency should be made. (No. 1) p Conclusion Ø Immediately after the accident, an Evacuation Area and Inhouse Evacuation Area were established, and cooperation of residents in the vicinity, local governments, police and relevant organizations facilitated the fast implementation of evacuation and “stay-in-house” instruction. As the accident became prolonged, the residents had to be evacuated or stay within their houses for long periods. Subsequently, however, it was decided that guidelines of the ICRP and IAEA, which have not been used before the accident, would be used when establishing Deliberate Evacuation Area and Emergency Evacuation Prepared Area. The size of the protected area defined after the accident was considerably larger than a 8 to 10 km radius from the NPS, which had been defined as the area where focused protection measures should be taken.
(6)Clear definition of widespread evacuation areas and radiological protection guidelines in nuclear emergency should be made. (No. 2) p Lessons learned Ø Based on the experiences gained from the accident, the Japanese Government makes much greater efforts to clearly define evacuation areas and guidelines for radiological protection in nuclear emergencies.
International criteria for the radiation protection was introduce to respond to the situation of accident continuation. 30
20 m. Sv/year was introduced for accident continuation. Standard for the radiation dose (1)Integrated radiation dose in the normal situation. • Public radiation exposure dose limit. 1 m. Sv/year Authority • Notice of Ministry of Economy, Trade and Industry • “Public notices which provides the dose limit based on the provisions of the rules about establishment operation etc. • Of the practical use nuclear reactors for electricity generation” Article 3: radiation dose out of the peripheral surveillance area. • ICRP recommendation Publication 60 (1990): Dose limit of the public radiation exposure. (2)Integrated dose at the time of the accident (a) Standard for avoiding large radiation exposure in the early stage of the accident outbreak 10 m. Sv (indoor sheltering) 50 m Sv (evacuation) • The guidance of the Nuclear Safety Commission • “About the disaster prevention measures such as nuclear energy facilities” • IAEA safety requirements GS-R-2 “Preparedness and Response for a Nuclear or Radiological Emergency” (2002) (b)Standard of the radiation Protection in the emergency situation(accident continuation) 20 -100 m. Sv • ICRP recommendation Publication 103 (2007) • IAEA safety requirements GSG 2 “Preparedness and Response for a Nuclear or Radiological Emergency” (2011) (C)The radiation protection Standard in the situation where the pollution after the accident has come to a settlement should be taken into the consideration 1 -20 m. Sv/year • ICRP recommendation Publication 103 (2007) • Reference level for protecting the public in the situation where the pollution after the accident has come to a settlement should be taken into the consideration (existing situation) ICRP: International Commission on Radiological Protection 31
(7) Safety regulatory bodies should be reinforced. (No. 1) p Conclusion Ø Governmental organizations have different responsibilities for securing nuclear safety. For example, NISA of METI is responsible for safety regulation as a primary regulatory body, while the Nuclear Safety Commission of the Cabinet Office is responsible for regulation monitoring of the primary governmental body, and relevant local governments and ministries are in charge of emergency environmental monitoring. This is why it was not clear where the primary responsibility lies in ensuring citizens’ safety in an emergency. Also, we cannot deny that the existing organizations and structures hindered the mobilization of capabilities in promptly responding to such a large-scale nuclear accident.
(7) Safety regulatory bodies should be reinforced. (No. 2) p Conclusion Ø Reflecting on the above issues, the Japanese Government separates NISA from METI and start to review implementing frameworks, including the NSC and relevant ministries, for the administration of nuclear safety regulations and for environmental monitoring.
(8) Legal structures, criteria and guidelines should be established and reinforced. (No. 1) p Conclusion Ø Reflecting on this accident, various challenges have been identified regarding the establishment and reinforcement of legal structures on nuclear safety and nuclear emergency preparedness and response, and related criteria and guidelines. Also, based on the experiences of this nuclear accident, many issues will be identified as ones to be reflected in the standards and guidelines of the IAEA.
(8) Legal structures, criteria and guidelines should be established and reinforced. (No. 2) p Lessons learned Ø Therefore, the Japanese Government reviews and improve the legal structures governing nuclear safety and nuclear emergency preparedness and response, along with related criteria and guidelines. During this process, it reevaluates measures taken against age-related degradation of existing facilities, from the viewpoint of structural reliability as well as the necessity of responding to new knowledge and expertise, including progress in system concepts. Also, the Japanese Government clarifies technical requirements based on new laws and regulations or on new findings and knowledge for facilities that have already been approved and licensed-- in other words, it clarifies the status of retrofitting in the context of the legal and regulatory framework. The Japanese Government makes every effort to contribute to improving safety standards and guidelines of the IAEA by providing related data.
(9)Human resources for nuclear safety and nuclear emergency preparedness and responses should be developed. (No. 1) p Conclusion Ø All the experts on severe accidents, nuclear safety, nuclear emergency preparedness and response, risk management and radiation medicine should get together to address such an accident by making use of the latest and best knowledge and experience. Also, it is extremely important to develop human resources in the fields of nuclear safety and nuclear emergency preparedness and response in order to ensure mid- and long-term efforts on nuclear safety as well as to bring restoration to the current accident.
(9)Human resources for nuclear safety and nuclear emergency preparedness and responses should be developed. (No. 2) p Lessons learned Ø Reflecting on the above-mentioned issues, the Japanese Government enhances human resource development within the activities of nuclear operators and regulatory organizations along with focusing on nuclear safety education, nuclear emergency preparedness and response, crisis management and radiation medicine at educational organizations.
(10) A safety culture should be thoroughly instilled. (No. 1) Ø Conclusion p All those involved with nuclear energy should be equipped with a safety culture. “Nuclear safety culture” is stated as, “A safety culture that governs the attitudes and behavior in relation to safety of all organizations and individuals concerned must be integrated in the management system” (IAEA, Fundamental Safety Principles, SF-1, 3. 13). Learning this message and putting it into practice is the starting point, the duty and the responsibility of those who are involved with nuclear energy. Without a safety culture, there will be no continual improvement of nuclear safety.
(10) A safety culture should be thoroughly instilled. (No. 2) p Lessons learned Ø Reflecting on this viewpoint, Japan establishes a safety culture by going back to the basics, namely that pursuing defenses in depth is essential for ensuring nuclear safety, by constantly learning professional knowledge on safety, and by maintaining an attitude of trying to identify weaknesses as well as room for improvement in the area of safety.
3. New framework of nuclear administration
3. 1 Establishment of new regulatory organization -New act “Act for Establishment of the Nuclear Regulation Authority”- 41
(1) Concept of protection of the environment is introduced for the first time into the purpose of the Act for Establishment of the Nuclear Regulation Authority. p In order to solve the problem caused by the removal of the problems of verticality of government organization with respect to the policy on the use of nuclear power, the administrative organization of the one responsible for the function of both the regulation and promotion of the use of nuclear energy, as well as always the occurrence of accidents in the use of nuclear power implementation you, or to develop the necessary measures in order to ensure safety in the use of nuclear power in light of international standards that standing recognition assumed that they must do one's utmost best and to prevent it, has been established the nuclear Regulation Authority as well as responsible to a central office to be exercised ex officio chairman and members of the Commission that is independent fairness neutral based on expertise, people's lives, property protection and health have , with the aim of contributing to the security of our country, as well as the preservation of the environment.
(reference) IAEA Safety Fundamentals [Principle 7: Protection of present and future generations] Ø People and the environment, present and future, must be protected against radiation risks.
(2) The NRA was established ensuring independence. Ø As a highly independent committee, the NRA was established as an external organ of the Ministry of the Environment. Ø Thorough separation of regulation and use, department of nuclear safety regulations of the Nuclear and Industrial Safety Agency was separated from the Ministry of Economy, Trade and Industry and was transferred to the NRA. Ø The NRA establishes its own rule of Standards for nuclear safety regulations, etc. Ø For ensuring nuclear safety, the NRA has the right of recommendations to the heads of the relevant administrative organs.
(3) The NRA has the Nuclear Regulatory Agency as the secretariat. Ø The NRA consists of Chairman and four members of the Commission. Ø As the secretariat of the NRA, the Nuclear Regulatory Agency was established.
(4) All the nuclear safety regulations are centralized into the NRA. Ø Regulation of Nuclear ship that the Ministry of Land, Infrastructure and Transport was responsible, regulation of nuclear power reactors that the Nuclear and Industrial Safety Agency of Ministry of Economy, Trade and Industry was responsible, regulation of research reactors and regulation of the use of nuclear fuel material that the Ministry of Education was responsible are centralized into the regulation of the NRA. Thus all the nuclear safety regulations are centralized into the NRA.
(5) All kinds of nuclear regulations are centralized into the NRA. Ø All kinds of nuclear regulations are centralized into the NRA. • Nuclear security • Nuclear non-proliferation safeguards • Radiation monitoring • Regulation of radioisotope
(6) The Nuclear Safety Commission was abolished when the new regulatory system was built. Ø The Nuclear Safety Commission was responsible for the so-called “double-check function. Ø The Nuclear Safety Commission was abolished and the necessary functions was integrated into the NRA. Ø The NRA formulates its own standards and guidelines which are required for nuclear safety regulations.
3. 2 Reinforcement of safety regulation -Revision of the Nuclear Reactor Regulation Law- 49
(1) Requirement of severe accident management was legalized. Ø Before the Fukushima accident, severe accident management is required on a operators’ voluntary basis. Ø Requirement of severe accident management was legalized after the accident.
Accident management were utilized to mitigate the condition of severe accident. Items Contents Alternative coolant injection • Lines via condensate water makeup systems from the condensate storage tanks as the water sources • Lines via fire extinguishing systems and condensate water makeup systems from the filtrate tanks as the water sources PCV vent facilities • PCV vent facilities were installed to bypass the standby gas treatment system so that they can vent the PCV when the pressure is high. Power interchange facilities • Power interchange facilities have been installed such that the power supply of the alternating current source for power machinery (6. 9 k. V) and the low voltage alternating current source (480 V) can be interchanged between adjacent reactor facilities (between Units 1 and 2, between units 3 and 4, and between Unit 5 and 6). 51
(2) The revised law requires the back fit system for existing nuclear facilities. Ø The revised law incorporates the latest findings on technical standards and introduces the system requiring compliance with the new standards for facilities also already obtained permission (back fit system). Ø In order to facilitate the rapid deployment of facilities related to nuclear power reactor facilities, the revised law introduces the system of type approval of equipment to eliminate duplication of examination licensing to improved safety, etc.
(3) Operational limits of 40 years for nuclear power plants are introduced. Ø The revised law defines 40 years as the time to drive a power reactor from the date that they pass the inspection before use. Ø However, the revised law gives a chance of the approval of the extension to the extent of the period specified by a Cabinet Order not exceeding 20 years, and only once under the condition that upon expiration of such period, a operator meets the standards established by the rules of the NRC to ensure the safety based on the situation of deterioration such as reactor caused due to the operation of a long period of time.
(4) Regulatory measures to ensure safety for facility which disasters occurred is introduced. Ø The revised law requires the operator to create implementation plans and to take measures along a line with that plan, when it is particularly necessary to manage the facility from the point of view of physical protection or prevention of disasters further at the facility which nuclear disaster occurs, after operators have taken emergency measures, and when the authorities specifies the nuclear facility as special nuclear facility.
3. 3 Reinforcement of emergency preparedness 55
(1) Nuclear emergency preparedness conference is established in the Cabinet. Ø Nuclear emergency preparedness conference is established in the Cabinet, under close collaboration with relevant organizations. Ø The conference promotes the implementation of measures to ensure the overall efforts of the government in case of nuclear accidents and to promotes the implementation of measures based on the nuclear emergency response guidelines. Ø The conference promotes the implementation of comprehensive measures to long-term efforts by a number of interested parties in the case of nuclear accident occurred. (Amendment of the Atomic Energy Basic Law)
(2) Disaster drills of nuclear operators are strengthened. Ø The NRA is able to check the status of the implementation of a nuclear operators’ emergency drills, to issue an order of necessary improvement and to give penalties for any violations.
(3) Function of “Nuclear Emergency Response Headquarters” is reinforces. Ø Prime Minister is designated as the head of the Nuclear Emergency Response Headquarters(NERH), Chief Cabinet Secretary, Minister of the Environment and chairman of the NRC are designated as deputy head of the NERH, and all the members the cabinet are designated as the members of the NERH , thus reinforcing the function of the NERH.
4. Situation of nuclear liability
Basic legal framework of nuclear liability was made in 1961. Ø Basic legal framework of nuclear liability was made in 1961. (1)"Law on Compensation for Nuclear Damage" • general framework (2) "Act on the indemnity agreement for compensation of nuclear damage" • Indemnification agreements between the operators and the central government
Ø • • Supplementary legal framework of nuclear liability was established due to large-scale damage caused by the Fukushima nuclear accident. (1)”Agency of Support for Nuclear Liability” was enacted on July 2011. All the electric utilities join this agency to support payment of nuclear liability by TEPCO. And the central government gives financial support to this agency. (2)”Act on Urgent Measures for Nuclear Damage related to the Accident of year Heisei 23” The Government makes a temporary payment in advance to the person to whom the specific nuclear damage was made in order to support the person. The amount of the temporary payment shall be in an amount not less than 1/2 of the estimated amount of a specific nuclear damage. 61
“Disputes Committee on Nuclear Liability” showed basic guideline for implementation of nuclear liability. Ø Eligible for compensation is as follows; • Residents in the areas related to evacuation • Agriculture, forestry and fishery businesses • Food industry • Tourist agent • Manufacturing companies • Service industry • Others Ø Compensation covers not only direct damage but also indirect damage and harmful rumor. 62
5. Reinforcement of safety of nuclear power plants
Countermeasures against tsunami were required to strengthen safety of BWRs. Fire Engine Power Supply Car Fuel Pool Reactor Containment DC Power Supply (Battery) Reactor Pressure Vessel Emergency Diesel Power Generator External Power Supply Alternative Water Injection Reactor Core Isolation Cooling System Emergency Reactor Cooling System Pressure Suppression Chamber Cooling Pump Ventilation Stack Sea Water Pump Pressure Suppression Chamber 電源車 64 64
Countermeasures against tsunami were required to strengthen safety of PWRs. External Power Supply Water Tank for Refueling Ｍ Turbine Driven Auxiliary Feed Water Pump To Fire Extinguisher Water System Diesel Pump for Fire Extinguisher Reactor Vessel Condensate tank (6) Connection of Power Supply Car Reactor Containment Spray Ｍ Ｍ Pressure Accumulat or Tank Contro l Rod Containment Spray Pump Main Steam Reactor Auxiliary Building Turbine Driven Auxiliary Feed Water Pump High Pressure Injection Pump Residual Heat Removal Pump Diesel Generator (7) Water Injection to Spent Fuel Pit Reactor Vessel Primary Coolant Pump Containment Sump Ｍ Component Cooling Water C Pump Ｍ Sea Water Pump To Sea To Steam Turbine Steam for Drive Main Water Supply Ｍ Ｍ Injection of Boric Acid Water Main Water Supply Electric Pump For Fire Extinguisher water Fresh Water Tank Fire Engine, etc. Water Supply Pressure Accumulator Tank Steam Generator Ｍ (3) & (4) Injection of Boric Acid Water from Pressure Accumulator tank, shut-off of the valve M External Power Supply Main Steam Generator Ｍ Emergency Diesel Power Generator (2) & (5) Water supply / cooling of steam generator, supply water to condensate tank Loss of Safety Pumps function (1) Loss of External Power Supply Spent Fuel Pit Ｍ Reactor Building Condensate Tank Reactor Containment Auxiliary Electric Water Supply Pump Fire Hydrant Water Supply water to make up for lowered water level boundar y Fire Engine Cooler Spent Fuel Pit (in auxiliary building) Cooling Pump (2 units) 65
Comprehensive safety assessment (stress test) are required to implement for other NPS. p Comprehensive safety assessments are conducted based on new procedures and rules, with reference to the stress tests introduced in Europe, for enhancing the safety of nuclear power stations and ensuring safety and reliance for citizens and residents. Ø Preliminary assessment: The nuclear power stations, that are under shutdown due to regular inspections and are prepared for start-up, are successively assessed on the safety margins of their facilities and equipment essential for safety against beyond-design-basis events. Ø Secondary assessment: Taking into account the implementation status of stress tests in Europe and what have been reviewed by the Investigation Committee on the Accidents at the Fukushima NPS, all nuclear power stations including the stations under operation and those evaluated in the preliminary assessment are assessed on the comprehensive safety margins. 66
In the stress test safety margins for structural integrity of components and piping are evaluated. Material strength confirmed by testing Elastic range Allowable limits of design standards Stress assumed to be exerted in design basis earthquakes (calculated value) Secondary Safety factors Preliminary Total margin Material strength defined in the standard Stress-strain curve Tension Irreversible deformation (plastic deformation) Fracture × Large load (fracture) Load (small deformation) Safety margins Values prescribed in the NSC Regulatory Guides and technical standards are used as allowable limits in preliminary assessment. Values exceeding allowable limits are applicable if it is technically verified in the preliminary assessment that the structure’s integrity and functions are maintained. Factual assessment is conducted during secondary assessment to obtain values that cause the loss of structural integrity and functions. Load removal (no deformation) Deformation 67
(reference ) Electricity production in Japan
Power generation capacity in Japan (from the bottom: nuclear, thermal (coal), hydro, thermal(natural gas), thermal(petroleum), pumped-storage, new energy) (Unit: 10000 k. W) 69
Power generation in Japan (from the bottom: nuclear, thermal (coal), hydro, thermal(natural gas), thermal(petroleum), pumped-storage, new energy) (Unit: 100 million k. Wh) 70
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