Fukushima Daiichi nuclear accident

    Background

    On 11 March 2011, a massive earthquake of magnitude 9.0 on the Richter scale jolted the eastern coast of Japan. An hour after the earthquake, a 14-15 m tsunami, as estimated at the Fukushima Daiichi site, hit the Pacific coastline and led to a terrible loss of lives (approximately 19 000 people died or remain unaccounted for). It also led to loss of all onsite power sources resulting in serious accidents at the three operating Fukushima Daiichi units, which were classified by the Japanese authorities as level 7 on the International Nuclear and Radiological Event Scale (INES).

    The accidents at Fukushima Daiichi Units 1, 2 and 3 were the result of the loss of offsite power caused by the earthquake, coupled with the loss of onsite power and the ultimate heat sink caused by the tsunami. Without a source of electrical power, the systems and components used to keep the fuel in the reactors cooled were not able to function. Although the operator attempted to implement alternative measures to cool the fuel, ultimately they were unsuccessful in preventing the fuel from overheating and melting. In addition, hydrogen generated during the accidents collected within the reactor buildings and caused explosions in the upper portions of the Unit 1, 3 and 4 reactor buildings, with significant damage to the top floors and exposure of the spent fuel pools to the environment.

    In response to this accident, NEA member countries decided to alter the work priorities of the NEA standing technical committees in order to assess the accident and to identify safety lessons.

    Work has been carried out on nuclear regulation, nuclear safety and research, crisis communication, radiological protection, decontamination and recovery, waste management, nuclear development, and nuclear liability and compensation

    In addition, the NEA has devoted significant efforts to directly supporting the technical needs of the Japanese government, with this assistance primarily focusing on 1) the recovery of land and decontamination, 2) the development and implementation of national reviews and stress tests and 3) enhancements to the regulatory infrastructure.

    Nuclear regulation

    Five Years after the Fukushima Daiichi Accident: Nuclear Safety Improvements and Lessons Learnt
    Countries around the world continue to implement safety improvements and corrective actions based on lessons learnt from the 11 March 2011 accident at the Fukushima Daiichi nuclear power plant. Published in February 2016, this report provides a high-level summary and update on these activities, and outlines further lessons learnt and challenges identified for future consideration. It focuses on actions taken by NEA committees and NEA member countries, and as such is complementary to reports produced by other international organisations.

    Report on the actions taken by the NEA member countries and standing technical committees in response to the Fukushima Daiichi NPP accident
    The report entitled The Fukushima Daiichi Nuclear Power Plant Accident: OECD/NEA Nuclear Safety Response and Lessons Learnt was published in September 2013. It outlines international efforts to strengthen nuclear regulation, safety, research and radiological protection in the post-Fukushima context.

    Precursor events
    A review of previous operating events that have significant similarities to the Fukushima Daiichi NPP accident has been performed to address the following questions:

    • Could the accident at Fukushima Daiichi have been prevented?
    • Can future severe accidents be prevented?

    Some responses and operating experience lessons learnt from the accident at Fukushima Daiichi are provided in the report on Fukushima Daiichi NPP precursor events issued in January 2014.

    Regulation of nuclear site selection
    The "Supplementary Report on the Regulation of Site Selection and Preparation" was issued in July 2014. It addresses additional siting issues, such as assessing impacts of multi-unit sites, seismicity, security, specific design features of the NPP against the fixed site parameters and public consultation during siting. It also provides more details on regulatory approaches for new reactor siting including changes or enhancements as a result of the Fukushima Daiichi NPP accident.

    Defence-in-depth (DiD) concept and implementation
    A workshop on Challenges and Enhancements to DiD in Light of the Fukushima Daiichi NPP accident was held on 5 June 2013. Consequently, a Senior Task Group on Defence-in-depth had been set up, inter alia, to produce a booklet in the NEA regulatory guidance series – commonly known as Green Booklets – in order to assist member countries in re-considering and clarifying DiD and its implementation in light of the Fukushima Daiichi NPP accident.

    Nuclear regulators effectiveness and safety culture
    The green booklet describing The Characteristics of an Effective Nuclear Regulator in terms of roles and responsibilities, principles and attributes was published in July 2014. In the same vein, another green booklet is under preparation to cover the policy aspects of the higher level attributes and behaviours that create a safety culture of the regulatory body.

    Accident management
    A three-year mandate of the Task Group on Accident Management (TGAM) has been established to review accident management practices in light of the Fukushima Daiichi NPP accident. Its objectives include identifying measures that should be considered to enhance the regulations and regulatory guidance for operators’ accident management activities. In February 2014, the task group published a report on accident management insights after the accident at Fukushima Daiichi. It is built on the existing bases for capabilities to respond to design basis events and accidents at NPPs, and what additional measures should be considered as an accident progresses to the severe accident stage.

    NEA met with Japanese officials to discuss nuclear safety regulatory organisations
    An NEA team of international experts met in Tokyo on 17-18 January 2012 with members of the Japanese Advisory Committee for Prevention of Nuclear Accidents and the special Japanese Task Force for the Reform of Nuclear Safety Regulations and Organisations to foster increased understanding of various national regulatory organisations and approaches to regulatory oversight of nuclear power facilities.

    The Fukushima Accident: Insights and Approaches
    A meeting of nuclear regulatory authorities of the G8, NEA member countries and other associated countries (Brazil, Bulgaria, India, Romania, South Africa and Ukraine) was held on 8 June 2011 to discuss insights gained in relation to the accident and decide on appropriate follow-up actions at the international level.
    Proceedings of the Forum on the Fukushima Accident: Insights and Approaches

    New avenues for improving international nuclear safety
    An International ministerial meeting co-organised by the French Presidency of the G8 and the NEA, with 37 countries in attendance was held on 7 June 2011.

    Nuclear safety and research

    New Expert Group on Accident Tolerant Fuels for LWRs
    Following two workshops held in 2012 and 2013 at the NEA, an Expert Group on Accident Tolerant Fuels (EGATF) was established within the Nuclear Science Committee in June 2014. This expert group will define and carry out a programme of work to help advance the scientific knowledge needed to provide the technical underpinning for the development of advanced LWR fuels with enhanced accident tolerance compared to currently used zircaloy/UO2 fuel systems. In particular, the proposed group will foster information exchange on material properties and relevant phenomenological experiments, carry out state-of-the-art reviews, organise benchmark studies and foster international collaborations regarding the development of core materials and designs which provide an improved tolerance to accidents.

    NEA/Japanese nuclear safety authority meeting on national safety reviews/stress tests
    NEA experts met in Tokyo with the Japanese Nuclear and Industrial Safety Agency (NISA) and the Japan Nuclear Energy Safety Organisation (JNES) on 16-18 November 2011 to foster a better understanding by NISA and JNES of other NEA member countries' post-Fukushima national safety reviews/stress tests, international guidance and review methodologies.

    Fukushima safety research activities

    Eight priority safety research activities were identified to address issues arising from the accident at Fukushima Daiichi:

    • Filtered containment venting – a summary of the current status of the technology and venting strategies as well as developments required for possible improvements to filtration technologies was completed in June 2014.
    • Hydrogen behaviour – a status report providing the current knowledge base of hydrogen behaviour, mitigation measures and computer code validation was completed in June 2014.
    • Probabilistic safety assessment (PSA) for natural external events – the proceedings for a workshop to share methods and commendable practises for PSA for natural external events were completed in June 2014.
    • Robustness of electrical systems – the proceedings for a workshop describing the technical basis of the provisions already taken or planned after the Fukushima Daiichi NPP accident regarding electrical sources, distribution systems and loads was due in December 2014.
    • Spent fuel pool loss-of-coolant accident (LOCA) – a status report of the knowledge base for spent fuel pool accident phenomenology and mitigation measures and a guide for further research activities was due in December 2014.
    • Metallic margins under high seismic loads – a summary of the technology base and design practises for assessing aged metal component and piping response to high seismic loads was due in December 2014.
    • Human performance under extreme conditions – the proceedings for a workshop summarising challenges during extreme events, good practises and knowledge gaps, and proposed principles for human performance under extreme conditions was due in December 2014.
    • Fission product release benchmark – an assessment of existing fast-running tools for their ability to model fission product release for a range of scenarioses and designs was due in June 2015.

    Joint nuclear safety research projects

    For more than 30 years, the NEA has provided a platform for interested countries to co-operate on a cost-sharing basis and pursue research on particular areas that would be difficult to deliver on a national basis.  Following the Fukushima Daiichi NPP accident, an NEA review of the joint research projects was carried out in 2012 known as Main Benefits from 30 Years of Joint Projects in Nuclear Safety (ISBN 978-92-64-99171-2), where a number of projects were identified that were already examining safety aspects of the accident.

    Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) Project
    A joint project was initiated in 2012 called, Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF). Eleven member countries (Canada, China, Finland, France, Germany, Japan, Republic of Korea, Russian Federation, Spain, Switzerland and the United States) are conducting a modelling study of the first six days of the accident. The first phase of the project is nearing completion, and discussions are underway for a second phase to begin in 2015.

    Three specific Fukushima-initiated projects

    Following the accident and this report, the NEA safety committees initiated three new joint projects based on existing research facilities to address safety issues related to the accident. These were HYMERES, PKL-3 and ATLAS.

    • Hydrogen Mitigation Experiments for Reactor Safety (HYMERES)
      This project uses existing test facilities in Switzerland and France and introduces new elements with respect to previous projects. The main objective of the HYMERES Project is to improve the understanding of the hydrogen risk phenomenology in containment in order to enhance its modelling in support of safety assessment that will be performed for current and new nuclear power plants. The project began in 2013 and will end in December 2016.
    • Primary Coolant Loop Test Facility (PKL-3) Project
      This project is based on an extension of an existing joint project at the Primärkreislauf-Versuchsanlage (primary coolant loop test facility) PKL in Germany. Relevant for current and new PWR plants, the PKL-3 is investigating safety issues relevant for current pressurised water reactor (PWR) plants as well as for new PWR design concepts and will focus on complex heat transfer mechanisms in the steam generators and boron precipitation processes under postulated accident situations. The project schedule is from April 2012 through the end of April 2016.
    • Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS) Project
      This project, operated by KAERI (Republic of Korea), is a large-scale thermal-hydraulic test facility that can simulate the thermal-hydraulic behaviour of major systems and components of a modern reactor design during real system transient and accident conditions. The intent of the work is to rapidly offer the ability to reconsider events that have an extremely low-occurring frequency, but result in a high core damage frequency, such as those found at the Fukushima Daiichi NPP. The project schedule is from April 2014 to March 2017.

    Further information on these and other joint projects can be found under NEA joint projects.

    Crisis communication

    NEA Working Group on Public Communication of Nuclear Regulatory Organisations (WGPC)
    The WGPC addressed the international dimension of the communicative responses to crises by assessing the experience of nuclear regulatory organisations (NROs) of NEA member countries and their stakeholders. Within this framework, a crisis communication workshop was held in Madrid on May 2012 and the report, Crisis Communication of Nuclear Regulatory Organisations: Towards global thinking, was issued in June 2013. In order to constantly improve communication, NROs invited external stakeholders to public communication workshops. The International Workshop with Stakeholders was held in April 2014. The next ones are scheduled for 2015 and 2016 in North America and Asia, respectively.

    Radiological protection

    International meetings on remediation and restoration of environments
    The NEA co-organised two days of international meetings on The Experience and Technology of Russia, Ukraine and Other CIS Countries on Remediation and Restoration of Environments on 3-4 February 2012. The meetings provided opportunities for experts from zones most affected by the Chernobyl accident to share best practices in managing contaminated land.

    International Workshop on Post-Accident Food Safety Science
    The NEA held an international workshop on Post-accident Food Safety Science in Fukushima, Japan on 8-10 November 2016. Hosted by the Cabinet Office of the Government of Japan, it brought together 137 participants, including experts and scientists from ten countries and local residents, to discuss the state of the art in post-accident food safety science; the local, national and international management of post-accident food safety; and approaches for addressing associated challenges.

    Decontamination and recovery

    International Symposium on Decontamination held in Fukushima, Japan
    The Government of Japan, in co-operation with the International Atomic Energy Agency (IAEA), the OECD Nuclear Energy Agency (NEA), the Japan Atomic Energy Agency (JAEA) and the Japan Nuclear Energy Safety Organisation (JNES), held an International Symposium on Decontamination – Towards the Recovery of the Environment, in Fukushima, Japan on 16 October 2011.

    Waste management

    Management of Radioactive Waste after a Nuclear Power Plant Accident
    The NEA Expert Group on Fukushima Waste Management and Decommissioning R&D (EGFWMD) was established in 2014 to offer advice to the authorities in Japan on the management of large quantities of on-site waste with complex properties and to share experiences with the international community and NEA member countries on ongoing work at the Fukushima Daiichi site. The group was formed with specialists from around the world who had gained experience in waste management, radiological contamination or decommissioning and waste management R&D after the Three Mile Island and Chernobyl accidents. The 2016 report provides technical opinions and ideas from these experts on post-accident waste management and R&D at the Fukushima Daiichi site, as well as information on decommissioning challenges.

    Nuclear development

    Impacts of the Fukushima Daiichi Accident on Nuclear Development Policies
    The Fukushima Daiichi nuclear power plant accident has had an impact on the development of nuclear power around the world. While the accident was followed by thorough technical assessments of the safety of all operating nuclear power plants, and a general increase in safety requirements has been observed worldwide, national policy responses have been more varied. These responses have ranged from countries phasing out or accelerating decisions to phase out nuclear energy to countries reducing their reliance on nuclear power or on the contrary continuing to pursue or expand their nuclear power programmes. The 2017 study examines changes to policies, and plans and attempts to distinguish the impact of the Fukushima Daiichi accident from other factors that have affected policymaking in relation to nuclear energy, in particular electricity market economics, financing challenges and competition from other sources (gas, coal and renewables). It also examines changes over time to long-term, quantitative country projections, which reveal interesting trends on the possible role of nuclear energy in future energy systems.

    Nuclear liability and compensation

    Japan's Compensation System for Nuclear Damage As Related to the TEPCO Fukushima Daiichi Nuclear Accident
    The NEA has prepared this publication in co-operation with the government of Japan to share Japan's recent experience in implementing its nuclear liability and compensation regime. The material presented in the publication should provide valuable insights for those wishing to better understand the regime applied to compensate the victims of the accident and for those working on potential improvements in national regimes and the international framework for third party nuclear liability.

    "Progress towards a global nuclear liability regime" (Nuclear Law Bulletin, No 93)
    During its April 2014 meeting, the Steering Committee for Nuclear Energy held a policy debate on "Progress towards a Global Nuclear Liability Regime". The Steering Committee heard presentations from several experts on nuclear liability issues. To prepare the delegates to the Steering Committee for the policy debate, the NEA Secretariat prepared a background note on the status of the nuclear liability regimes, as well as on current issues and challenges in implementing the regimes.

    Further information

    OECD Nuclear Energy Agency (NEA) follow-up to the TEPCO Fukushima Daiichi nuclear accident
    Extracts from NEA News
    The NEA has undertaken a number of activities following the March 2011 accident at the Fukushima Daiichi nuclear power plant in Japan. This brochure contains three extracts from NEA News published in the months following the accident: Fukushima (what happened, consequence, follow-up), published June 2011; Fukushima: liability and compensation, published December 2011; and The NEA integrated response to the Fukushima Daiichi nuclear accident, published June 2012. Together these extracts help the reader to better understand the causes, consequences and importance of the NEA's response to the Fukushima Daiichi accident (2012).


    Last reviewed: 5 June 2017

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