The Fukushima Daiichi nuclear power plant accident. OECD/NEA nuclear safety respons and lessons learnt
|Classificatie||184.108.40.206/10 (JAPAN - FUKUSHIMA (Dai’ichi ongeluk))|
|Opmerking||Online available at OECD website|
Uit de publicatie:
Executive summary The Fukushima Daiichi nuclear power plant (NPP) accident that occurred on 11 March 2011 following a massive earthquake and tsunami was one of the most severe accidents ever experienced at a nuclear power plant and will have to be dealt with for many years by those in charge of nuclear safety (operators, safety bodies). Following the accident, nuclear regulatory authorities, governments and international organisations around the world took immediate actions to support Japan in its response. Under the control of nuclear regulatory authorities, operators began undertaking a series of analyses and follow-up measures to ensure the safety of all nuclear facilities. This report outlines the actions taken by the OECD Nuclear Energy Agency (NEA) and its member countries. Key messages and their implications for ensuring high levels of nuclear safety are also summarised. At the national level, all NEA member countries with nuclear power plants took early action to ensure and Key messages confirm the continued safety of their operating NPPs and • NEA member countries implemented the protection of the public. After these preliminary focused safety reviews of their safety reviews, all countries with nuclear facilities operating reactors and determined carried out comprehensive safety reviews, often referred that they were safe to continue to as “stress tests”. These comprehensive safety reviews operation. Additional safety reassessed the safety margins of nuclear facilities with a enhancements that will help to primary focus on challenges related to conditions better cope with external events experienced at the Fukushima Daiichi NPP, for example and severe accidents have been extreme external events and the loss of safety functions, identified and are being or capabilities to cope with severe accidents. The reviews implemented. examined the adequacy of design-basis assumptions as well as provisions for beyond-design-basis events. NEA member countries with nuclear power plants evaluated, and when warranted, took actions to improve the safety of the plants. They also undertook to upgrade existing safety systems or to install additional equipment and instrumentation so as to enhance the ability of each plant to withstand a natural event that disrupts access to the electrical power grid and/or ultimate heat sink for an extended period, including events that affect all the reactors at a single site simultaneously (multi-unit events). In the weeks following the accident, the NEA already began establishing expert groups in the nuclear safety and radiological protection areas as well as contributing to information exchange with the Japanese authorities and other international organisations. It promptly provided a forum for high-level decision makers and regulators within the G8-G20 frameworks. Effective implementation is being sought of actions aimed at making it extremely unlikely that an accident similar to that of the Fukushima Daiichi NPP accident could occur in the future. The main focus is on Key messages enhanced application of the defence-in-depth concept to ensure robustness against external threats and on • Nuclear safety professionals have accident management practices to face loss of safety a responsibility to hold each other functions. In addition, countries are improving their accountable to effectively implement knowledge of the behaviour of spent fuel pools (SFPs) nuclear safety practices and concepts. under accident conditions; gaining better under- • The primary responsibility for nuclear standing of staff performance under stressful condi- safety remains with the operators of tions through human performance/factors analysis; the NPPs, and regulatory authorities and reviewing and improving crisis communication, have the responsibility to ensure that emergency procedures and guidance. Actions are also the public and the environment are being undertaken to improve the effectiveness of protected. emergency plans, in particular in situations with severe damage to the local, national or regional infrastructure that could be caused by an external initiating event. Research and development programmes related to severe accidents and probabilistic safety assessments (PSAs) considering natural hazards are being conducted as well. In addition to revising regulatory requirements to better cope with external hazards and severe accidents, many countries, and the international radiological protection community in general, are revisiting approaches to emergency management and recovery in order to be better prepared nationally for accident situations. This includes reviewing national preparations for post-accident recovery and for transition from the emergency to the recovery phase. Improvements in international communications and exchange of information and expertise among regulatory authorities, their technical crisis centres and relevant international organisations are also being studied and implemented. Two years after the accident, the NEA continues to assist the Japanese authorities in dealing with their recovery efforts, associated challenges and research plans. Current issues include more comprehensive safety reviews, decontamination, radiological protection and stakeholder dialogue. The NEA is also supporting research programmes designed to improve understanding of how the accident progressed as well as to obtain safety-related information during decommissioning and dismantling. Based on experience from the Three Mile Island and Chernobyl accidents, a full analysis of the Fukushima Daiichi NPP accident will take many years. The NEA is working with the Japanese authorities on the development of the research plans to collect the information needed to better understand what happened as the accident progressed at each of the units. Associated activities will continue for several years and new activities may also be needed in the future. The key messages and conclusions drawn from the post-accident activities and the implications they have on ensuring that high levels of nuclear safety are continuously maintained and improved internationally are outlined below. Key messages First among these is that NEA member • There is no room for complacency countries using nuclear power promptly imple- in the implementation of nuclear mented focused safety reviews of their operating safety practices and concepts. reactors, considering such impacts as those related • The Fukushima Daiichi NPP to extreme external events, and determined that accident identified significant they were safe to continue operation while more human, organisational and cultural comprehensive safety reviews were conducted. challenges, which include ensuring Additional safety enhancements that will help to the independence, technical better cope with external events and severe capability and transparency of the accidents have been identified and are being imple- regulatory authority. mented in NEA member countries. A fundamental message from the accident is that there is no room for complacency in the implementation of nuclear Key messages safety practices and concepts. • The fundamental concepts of The existing national and international requirements defence-in-depth remain valid and already in place provide an effective framework for acci- continue to be shared by those in dents within the design basis, and efforts are underway to charge of nuclear safety. enhance these frameworks to better address accidents that, although unlikely, could result in catastrophic consequences if unmitigated. Nuclear safety professionals have a responsibility to hold each other accountable to effectively implement nuclear safety practices and concepts. Recognising that the primary responsibility for nuclear safety remains with the operators of the NPPs, regulatory authorities have the responsibility to ensure that the public and the environment are protected from the harmful effects of radiation. Although the accident at the Fukushima Daiichi NPP overwhelmed essentially all the engineering and procedural barriers to the offsite release of radioactive material, the fundamental concepts of defence-in-depth still remain valid and continue to be shared by those in charge of nuclear safety. Where there is higher uncertainty, as in the case of external hazards, effective implementation of the defence-in-depth concept requires additional measures to address these uncertainties to maintain adequate safety margins. There are lessons being learnt, analyses being conducted, and information being collected to support safety enhancements to cope with events that go beyond the design basis. This report has shown that there would be benefit from having guidance from regulatory authorities in each country on the application of DiD in such areas as: a) prevention and mitigation at each level1 of DiD, b) to ensure that actions taken and resources relied upon at one level of DiD can be made independent from the other levels, and c) to minimise the potential for common-cause failures propagating from one level to another. The Fukushima Daiichi NPP accident identified significant human, organisational and cultural challenges that need to be addressed. Such challenges include ensuring the independence, technical capability and transparency of the regulatory authority. The diversity of national recommendations during emergencies, and in particular the differences between Japanese protection recommendations and those of foreign governments for their own citizens in Japan, suggests that mechanisms to share technical information among governments should be improved. It has been recognised that significant improvements are needed in national and international communications and information exchange among national regulatory organisations and their crisis response centres. The international information exchange aspects of nuclear emergencies are also being reviewed internationally in a drive to improve all communication aspects among countries that could be directly or indirectly affected by nuclear Key messages emergencies. • Since an accident can never be The NEA International Nuclear Emergency Exercises completely ruled out, the necessary (INEX) have focused on this issue, and will continue to provisions for dealing with and study national approaches to making related decisions. managing a radiological emergency In addition, should a large accident occur, there could be situation, onsite and offsite, must be a need for urgent actions in countries adjacent to the planned, tested and regularly accident state. reviewed. The implementation of protective measures remains Key messages problematic, in particular as the situation transitions to • Ensuring safety is a national longer-term recovery, and those evacuated wish to return responsibility but poses a global to their normal lives. This transition requires significant concern due to potentially far- resources and efforts to effectively engage with stake- reaching accident consequences. holders so as to understand and appropriately address their concerns. This is particularly complex in a post- • Complete experience feedback from accident situation where public trust may often be low. the Fukushima Daiichi nuclear power plant accident will take many years. To date, a considerable amount of work has been • A questioning and learning attitude completed to gather in-depth experience and feedback is essential to continue improving from the Fukushima accident, but much more remains the high level of safety standards to be done by the whole nuclear community. As the and their effective implementation. accident-recovery process continues to evolve and reach specific conclusions, the latter could have an effect on the long-term recommendations for research and development. Such work could be included in NEA ongoing research, with the goal of developing enhanced analysis methods for those areas that were found to require increased scrutiny following the preliminary safety assessments and technical evaluations carried out after the accident (i.e. severe accidents, external hazards assessments). These and other activities, some to be identified, will continue for several years to come. For medium- and longer-term actions to address lessons learnt, international co-operation provides a forum for collecting, sharing and analysing data to develop consistent approaches that can be applied within the national regulatory framework. This international co-operation also provides a forum in which peer regulators can actively encourage each other to remain vigilant in ensuring the safety of their nuclear power plants and help avoid the complacency that contributed to the accident at the Fukushima Daiichi NPP. Since an accident can never be completely ruled out, the necessary provisions for dealing with and managing a radiological emergency situation, onsite and offsite, must be planned, tested and regularly reviewed in order to integrate experience feedback from drills and from the management of real-life situations. As a complement to these safety provisions, the NEA will continue working on appropriate communication of nuclear risks. Following the large societal, economic and psychological impacts of the accident, the nuclear safety organisations considered that provisions should be identified to prevent and mitigate the potential for severe accidents with long-term, offsite consequences. To conclude, it is the collective responsibility of nuclear safety professionals to ensure that there is no complacency in the effective implementation of the practices and approaches that have been developed over decades of use of nuclear power to protect the public and the environment from the harmful effects of radiation. A questioning and learning attitude is essential to continue improving the high level of safety standards and their effective implementation. Ensuring safety is a national responsibility but poses a global concern due to potentially far-reaching accident consequences. Within this context, international co-operation is important for identifying commendable practices to ensure that nuclear safety is effectively addressed within the national regulatory framework of countries with nuclear power programmes. The NEA provides an effective forum for this international co-operation. Working together through international co-operation, regulatory authorities can identify commendable practices that will support national programmes as they develop and implement the medium- and longer-term actions in response to the lessons learnt from the accident.
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