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Deterministic and probabilistic beyond design basis safety analyses need to be comprehensive and take into account both internal and external events, including internal flooding and external hazards such as seismic events and flooding. |
The combination of DSA and PSA needs to be used to assess factors such as cliff edge effects, realistic equipment and personnel performance, and the relative contribution of various accident sequences to the overall plant risk. For the sequences with the highest possibility of contributing to core damage or challenging the containment integrity, the operating organization should evaluate the need for taking actions to mitigate the consequences of these sequences. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=100 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Extremely low numerical values from PSAs need to be reviewed and confirmed. |
Comparison of the CDF calculated for the Fukushima Daiichi NPPs to the worldwide average for similarly designed BWRs would have indicated that the values calculated by TEPCO were at least two orders of magnitude lower than the other plants. This difference should have been investigated which may have highlighted weaknesses in the procedures and training being used at the Fukushima Daiichi NPP. However, this investigation was not conducted, which highlights the issue that numerical values obtained from PSAs need to be used with caution when making decisions about the overall safety of the plant. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=100 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Accident management provisions need to be clear, comprehensive and well designed. |
Accident management strategies need to be based on a plant specific analysis performed by using a combination of deterministic and probabilistic approaches. Accident management guidance procedures need to consider events taking place in several units simultaneously and in SFPs. These provisions need to take into account disrupted regional infrastructure, including serious deficiencies in communication, transportation and utilities. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=117 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Regulatory bodies need to ensure that adequate AM provisions are in place, taking into account severely damaged infrastructures and long duration accidents. |
The Nuclear Safety Commission (NSC) recommended in 1992 that the regulatory body and the utilities introduce AM measures, although this had not been a requirement. In response, TEPCO had developed emergency and AM procedures. An IAEA IRRS mission to Japan in 2007 noted that AM measures were “taken by licensees on a voluntary basis” [51]. Therefore, it was suggested that the regulatory body develop a systematic approach for BDBAs, and the complementary use of PSAs, and SAM in the assessment process was recommended. However, no effective action was taken. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=117 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Training and exercises need to be based on realistic severe accident conditions. |
Special attention in personnel training needs to be devoted to performing actions under conditions of prolonged SBO with limited information about the plant status or the unavailability of important safety parameters. Staff training, exercises and drills need to realistically simulate the progression of severe accidents, including the simultaneous occurrence of accidents in several units. Training, exercises and drills need to involve not only on-site AM personnel or personnel executing on-site emergency plans, but also all off-site responders at corporate, local, regional and national levels. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=117 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Provisions for the proper management of hydrogen need to be considered. |
The hydrogen explosions at the Fukushima Daiichi NPP significantly affected the ability of operators to respond to the accident. Hydrogen monitoring and removal equipment should be installed in the plant to prevent hydrogen deflagration or explosions. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=117 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Where several bodies have responsibilities for safety, the government needs to effectively coordinate their regulatory functions to avoid omissions or duplications that may jeopardize safety. |
The Japanese nuclear legal framework comprised numerous laws and arrangements at different governmental levels that had been revised over the years in response to accidents and incidents. Many government ministries, agencies and quasi-governmental organizations played influential roles with regard to the utilization and regulation of nuclear energy in Japan. These complex arrangements appear to have hampered the implementation of effective actions and regulatory activities for enhancing safety. The NSC was an important body with both advisory and supervisory roles in the system of subsequent regulation review. In the opinion of the IAEA’s IRRS mission, the role of NISA as the regulatory body in relation to NSC was in need of clarification. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=132 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The regulator should require that the operator of a facility update its safety demonstration on an ongoing basis to reflect changes in the status of the facility. |
Although improvements in safety rely primarily on the actions of operators, regulatory oversight will be a driving force. In particular, regulatory bodies should promote continuous safety improvement processes, fostering an environment that encourages licensees to invest in improvements beyond national requirements. The regulatory body needs to review and approve the safety demonstration. In addition, any proposed modification of a facility that might significantly affect safety needs to be subject to review and assessment by the regulatory body. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=132 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Regulatory independence, competence, strong legislative authority and adequate resources, including qualified personnel, are essential in order to perform the required regulatory functions. |
NISA lacked the requisite de jure independence from the entities responsible for the promotion of nuclear energy. In addition, the budget pressures and administrative rules for job rotation of civil servants to which NISA was subject limited the technical and regulatory competence of its staff. The regulatory body needs to make independent regulatory judgements and decisions, free from any undue influences that might compromise safety, such as pressures associated with changing political circumstances or economic conditions, or pressures from government departments or from other organizations. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=132 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The regulatory body needs to review and inspect the safety of a facility throughout its lifetime. |
The goal is to verify: the extent to which the facility conforms to safety standards and practices; the extent to which the licensing basis remains valid; the adequacy of the arrangements that are in place to maintain safety until the next PSR or the end of plant lifetime; and the safety improvements to be implemented to resolve the safety issues that have been identified. These reviews and inspections require unimpeded access to documentation and the plant. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=132 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The accident at the Fukushima Daiichi NPP was a surprise outside the boundaries of the basic assumption of the key stakeholders, meaning the stakeholders had not been able to imagine that such an accident could occur. From this, the lesson learned for the international nuclear community is that the possibility of the unexpected needs to be integrated into the existing worldwide approach to nuclear safety. |
When unexpected situations occur outside the boundaries of the basic assumption of nuclear safety, people and organizations need to be prepared to be unprepared. Resilience competencies and resources have to be developed well in advance within organizations to help personnel to quickly and flexibly adapt to new situations, to develop new solutions for blind spots — in other words: to be resilient in unexpected situations. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=157 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Individuals and organizations need to consciously and continuously question their own basic assumption and their implications on actions that impact nuclear safety. |
This is part of sustainable safety culture improvement; the basic assumption about safety is recognized as fundamentally directing safety culture. To enable this, individuals and organizations need to systematically question the nature, boundaries and potential challenges of one’s own assumptions of nuclear safety, particularly beyond technical safety matters. Reflection and dialogue are needed within an organization in order to become aware of possible blind spots in basic assumptions. This can be achieved through periodic safety culture assessments (both independent and self-assessment reviews) based on the IAEA’s approach to the assessment of safety culture and other IAEA peer reviews, such as the IAEA’s IRRS and OSART missions. In addition, the utilization of a diversity of expertise and experience is important in order to avoid undue simplifications in interpretations and to better recognize the full picture. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=157 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Nuclear organizations need to critically review their approaches to emergency drills and exercises to ensure that they take due account of harsh complex conditions and unexpected situations. |
Harsh complex conditions include both physical and psychological aspects. Unexpected situations that may be considered for implementation in the framework of emergency exercises include a shaking ground (earthquake), large scale fires and flooding, a dark work environment, unfamiliar sounds and the loss of vital information. In addition, resilience competencies need to be developed well in advance to prepare humans and organizations for quick and flexible adaptation to unexpected situations (‘unknown unknowns’). |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=157 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The results of research on complex sociotechnical systems for safety need to be taken into account. |
In order to proactively deal with the complexity of nuclear operations, licensees, regulators, designers, peer reviewers and other relevant stakeholders need to consider the research on sociotechnical systems when designing nuclear technology, operating and overseeing nuclear installations and developing industry standards. The development of human and organizational resilience capabilities should also be based upon state of the art research on complex sociotechnical systems. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=158 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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A systemic approach to safety needs to be taken in event and accident analysis, considering all stakeholders and their interactions over time. |
Stakeholders include, among others, licensees, regulators, political leaders and the public. The systemic approach includes human, technological and organizational considerations and is necessary to understand how the components of the overall (sociotechnical) system functioned, interacted and succeeded in everyday situations and over the decades before the accident, as well as during accident response. To accomplish this, a diversity of expertise is needed to cover the human, technical and organizational factors. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=158 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The regulatory body needs to acknowledge its role within the national nuclear system and the potential for its impact on the nuclear industry’s safety culture. |
The regulatory body has the challenging role of questioning the nuclear industry’s approach to safety. Therefore, the regulatory body needs a critical, profound self-reflecting and questioning ability. This may include institutionalizing an ongoing dialogue within the organization and with other stakeholders on the regulatory body’s safety culture and its impact on nuclear safety. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=158 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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Licensees, regulators and governments need to conduct a transparent and informed dialogue with the public on an ongoing basis. |
This may include explanation of the risks that the use of nuclear technology for energy production entails. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=158 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The effectiveness of operating experience programmes needs to be confirmed periodically and independently through a detailed review of the specific actions taken in response to international operating experience. |
This review can be made a standard part of existing oversight processes considering relevant sources such as the Incident Reporting System (IRS) by the IAEA and the OECD/NEA. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=169 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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When assessing the applicability of significant operating experience with limited consequences, it needs to be considered whether the consequences could have been much worse had there been a small difference in the initiating event, or in the progression of the event. |
When assessing the applicability of significant operating experience, the potential for similar consequences from different initiators needs to be considered. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=169 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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The operating experience programme needs to function within a management system where nuclear safety is paramount and overrides all other demands. |
The management system needs to include objective risk informed decision making criteria to support decisions for retrofitting safety design improvements. It is important to periodically check if the organization is effectively upholding nuclear safety as the overriding priority. |
| Reference Document:
The Fukushima Daiichi Accident - Technical Volume 2 - Safety Assessment |
| Link to Reference Document:
<a href=http://www-pub.iaea.org/MTCD/Publications/PDF/AdditionalVolumes/P1710/Pub1710-TV2-Web.pdf#page=169 target='_blank' alt='Open site in new window'><img src='/FukushimaLessonsLearned/Images1/Thumbnails/external-link-xxl.gif' style='height:25px; width:25px;' /></a> |
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