In 2013, the Nuclear Energy Agency (NEA) published a report into the Fukushima accident, identifying actions to be taken in the light of experiences gained. The most important conclusion reached in the 2013 report was that, in the aftermath of the accident, nuclear power plants in Nuclear Energy Agency (NEA) member countries were safe. Nevertheless, there were many lessons learned, and nuclear power plants are safer because of actions taken in response to the lessons learned.

NEA has produced a new report, ‘Five Years after the Fukushima-Daiichi Accident: Nuclear Safety Improvements and Lessons Learnt’, which focuses on what has been done by the NEA and its member countries to improve safety, and to build on the 2013 report. The report identifies the following:

  • Actions taken by regulatory authorities in NEA member countries that have led to the establishment of new requirements resulting in specific nuclear power plant improvements in multiple areas.

  • Actions to underline the importance of using operating experience and risk insights through international cooperation.

  • Activities to improve regulatory frameworks in member countries.

  • Research undertaken to improve knowledge and understanding of the accident.

  • Activities implemented to improve emergency preparedness and radiological protection.

  • Efforts to understand and characterise the importance of strong nuclear safety cultures.

  • Actions taken to continue enhancing stakeholder involvement and public communication.

  • Legal improvements, including liability law.

Enhancing safety is a common objective around the world. However, NEA member countries have addressed it using different approaches. Some national standards or safety requirements are country-specific, and member countries are not necessarily starting from the same point.

Some improvements have already been implemented, some are in the process of being completed, and some are being planned and will be implemented in the near future. 

In several countries, governments have also taken action to reinforce the independence of their regulatory bodies.

One element that has been identified where safety can be improved is related to the potential impact of external hazards, along with plant improvements related to the diversity of equipment, enhancements in the robustness of safety functions, and continuing efforts to improve organisational behaviours. Actions taken in these areas have resulted in:

  • A re-examination of external hazards.
  • An improvement of the robustness of the electrical systems.
  • An enhancement of the robustness of the ultimate heat sink (UHS).
  • Protection of the reactor containment system.
  • Protection of spent fuel in storage pools.
  • Reinforced capability to rapidly provide diverse equipment and assistance from onsite or offsite emergency preparedness facilities.
  • A reinforced safety culture, including human and organisational factors in decision making during emergencies.
  • Continued safety research.

NEA identified an important need to better develop and enhance the approach taken to the evaluation and inclusion of external hazards in the safety analysis. It was generally concluded that there has traditionally been a more thorough and detailed inclusion and consideration of internal hazards in safety analyses and safety cases. Consequently, member countries have re-examined the response to external hazards, including those of higher magnitudes than had previously been considered, and have used the latest data technology to identify and consider plausible combinations of sequential and consequential events.

Many countries have focused on the robustness of electrical systems. As a result, nuclear power plants in these countries are in the process of upgrading the capability of existing power supplies as well as installing new, dedicated equipment to ensure that there are redundant and diverse sources of electrical power available following a significant event. Measures have included new or improved fixed installations as well as additional mobile power sources.

Ensuring heat can be removed from the core in the event of an extreme natural event has led some countries to consider bunkered safety systems, designed to resist extreme natural events. Many countries have now installed or are considering strategic placement of portable equipment that can be quickly positioned and provide emergency cooling. Some countries have enhanced the decay heat removal function by providing an alternate path for cooling water supply, arranging for passive cooling or identifying an alternate heat sink.

The ability of spent fuel pools (SFPs) to cool and protect spent nuclear fuel was a challenge during the Fukushima accident. Although no damage occurred to any of the SFPs or to the spent fuel at Fukushima, NEA member countries have taken actions to improve the protection of SFPs. For example, protection of SFPs against external events has been reassessed in some countries, and has led to the installation of redundant SFP level and temperature indications, as well as diverse cooling water supplies.

Some countries require portable safety equipment be stored in a protected manner at the site, to provide redundancy and diversity of equipment during a significant event. Some countries have decided to establish offsite equipment storage facilities, capable of transporting a full range of equipment to a facility within hours of an event. These facilities are located far enough away from the nuclear power plant that a natural disaster at the plant would not affect the off-site facility.

After implementing actions resulting from reviews and self-assessment, member countries have found that, in general, nuclear safety, emergency preparedness, and response arrangements have improved. They have also acknowledged that more needs to be done.

National safety frameworks are being improved to reinforce the effective independence of regulatory bodies and to update regulations. International cooperation is also increasing, with greater participation in peer reviews and more information exchanged. International collaboration is growing, and this is reinforcing global nuclear safety.

The Committee on Nuclear Regulatory Activities (CNRA) has reached consensus on various reports and documents providing best practices and guidance in accident management, crisis communication, precursor events, defence in depth, regulatory effectiveness, safety culture and the regulation of new reactors. These guidance and best practices are designed for countries with existing, mature regulators, and can be used to improve policies and practices, benchmark and train staff. They can also be useful for new entrant countries in the process of developing and maintaining an effective nuclear safety regulator.

Report conclusions – Continuing enhancement of safety

NEA member countries have sought to learn lessons from the Fukushima accident. The report examined prompt actions and analyses at national and international levels to ensure safety. NEA member countries have continued to take appropriate actions to maintain and enhance the level of safety at their nuclear facilities. As a result, nuclear power plants are safer.

Ensuring safety is a continual, evolving process. Safety is the prime responsibility of the operator, and the goal of the regulator is to ensure operators continuously improve and make nuclear facilities safer. The continued operation of nuclear power plants requires that their robustness to extreme situations be reinforced beyond design basis safety margins, and many of these improvements have either been, or are in the process of being, implemented.

While an external event caused the Fukushima accident, the actions that have been taken around the world to improve nuclear power plant safety are applicable to any type of event.

Effective implementation of safety improvements

Nationally, NEA members have all discussed the same lessons learnt from the Fukushima accident, and the outcomes being sought are very similar. However, different avenues are being taken to achieve the goals of enhancing safety, and preventing and mitigating potential accidents.

Member countries face unique natural conditions, particularly with regard to extreme events. Different countries have different national regulatory requirements for the prevention and mitigation of severe accidents, different approaches to and applications of periodic safety reviews to continuously improve safety, and different types and generations of reactor.

Since national standards are country- specific, and reflect operating experience from the particular country or regulatory practices within the country, member countries are not necessarily starting from the same start point. Different member countries have differences in the priorities and implementation of schedules for safety improvements.

Using operating experience and risk insights

Lessons learnt concerning operating experience have been disseminated internationally, particularly in relation to
the main initiators and conditions that were observed during the Fukushima accident. The accident did not reveal any unknown initiators, sequences or consequences. However, the combination and severity of the initiating events had never occurred before, and the evolution of the accident in three different units simultaneously was also new.

The Fukushima accident demonstrated that while existing operating experience feedback systems provide a good tool to learn lessons and help prevent the events recurring, operating experience combined with risk insights can provide an even greater source of potential improvement, as demonstrated in the course of real events.

Timely implementation of nuclear power plant operating experience is a continuous challenge for both regulators and operators. The challenge is to identify precursor events and the subsequent lessons learnt, and then to implement the related actions to enhance plant safety and prevent recurrence.

Strengthening regulatory frameworks

National safety frameworks have been and are being strengthened to enhance governmental frameworks and update regulations, including through reinforcing the independence of regulatory bodies. The principle of regulatory independence, in particular the effective separation between the functions of the regulatory body and those of any other body or organisation concerned with the promotion or use of nuclear energy, is fundamental, and it requires vigilance to ensure that it is maintained.

Some member countries have reviewed, and other member countries are in the process of reviewing, their regulatory frameworks and are making changes as appropriate to update their legislation so as to reflect lessons learnt from the Fukushima accident. One example is the emphasis on ensuring that a clear and comprehensive legal framework exists to allow the operator of a nuclear installation – and its government, if necessary – to quickly react and adapt to the specific circumstances of an event to ensure timely and financially adequate compensation to victims.

Member countries have done a lot of work in benchmarking and continuously improving their nuclear safety frameworks and regulations. This has included activities on accident management, crisis communication, precursor events, defence in depth, regulatory effectiveness, safety culture and regulation of new reactors. International cooperation is also increasing, with greater participation in benchmarking of effective regulatory practices and exchanges of information.

Long-term learning process

As was the case with the Three Mile Island and Chernobyl accidents, implementation of lessons learnt from the Fukushima accident and the continuation of related research activities are long-term actions that will evolve into the future as regulators and the nuclear industry continue to learn from the accident.

While near-term, higher priority lessons learnt are being addressed, our knowledge base will expand as the Fukushima units are decommissioned. Efforts such as the NEA Senior Expert Group on Safety Research Opportunities Post-Fukushima (SAREF), and the NEA Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF) have already provided valuable insight concerning severe accident progression and the current status of reactors in all three units that experienced core melt.

Research is being continued into accident progression, recovery, and the human factors involved in severe accident response. Important information is emerging from post-accident recovery efforts at Fukushima.

The human element in safety

Human and organisational factors and safety culture are essential to all aspects of nuclear safety, from design, construction and operation to the response to potential events or accidents. Both licensees and regulatory bodies identified these as relevant issues to be addressed in the post-Fukushima accident assessment. The human element has a considerable impact on all levels of the defence-in-depth concept.

Work carried out by the NEA and the member countries on the characteristics of an effective nuclear regulator and on regulatory safety culture have been recommended for benchmarking, peer review, and for training and development of regulatory staff.

Several NEA member countries have initiated a broad consideration of safety culture characteristics, including human and organisational factors. These initiatives include specific safety culture programmes that focus on attitudes towards safety, organisational capability, decision-making processes and the commitment to learn from experience. Going forward, the NEA and its member countries recognise that nuclear safety will benefit from continuing work in such areas as safety culture, and human and organisational factors.

Emergency management and long-term commitment of resources

The Fukushima accident demonstrated the challenges involved when managing the consequences of a large-scale accident. As time progressed, radiological and social consequences became increasingly evident, while decisional responsibilities were shifting from central government to regional and local governments, and to affected individuals. Approaches to address the complexity generated by such long-lasting circumstances must be considered and included in national planning.

Moreover, the resources needed to manage an emergency on the scale of Fukushima accident have proved to be considerable. Non-accident countries, even those not directly affected, expended significant resources on understanding the rapidly evolving situation so as to support recommendations on how best to protect expatriate populations in Japan, address issues of people and cargo arriving from Japan and manage food emanating from Japan. The Japanese government was challenged by the need to expend significant resources to address the accident situation, and simultaneously dedicate resources to formally and informally address questions from other countries and from international organisations. Emergency management planning should therefore take into account the Japanese experience in terms of training and resources required to be appropriately prepared to manage the collection and flow of information.

Enhancing stakeholder involvement and public communication

It is appropriate to involve stakeholders (local authorities, industry, non-governmental organisations, government officials and the public) in decision-making. This helps to enhance the credibility, legitimacy, sustainability and final quality of regulatory and offsite emergency management decisions. In addition, regular communications with stakeholders is highly desirable to improve their understanding in times of crisis.

Some member countries have further developed their policies on transparency, openness and involvement of stakeholders in the regulatory process, providing a window into the regulatory decision-making process. Different country-specific practices and regulatory requirements reflect more general practices within each individual country.

Experience from the Fukushima accident highlighted the need to reconsider approaches to information sharing and assessment, both domestically and internationally.

The experience reaffirmed that regulators and governments should be effectively communicating with their stakeholders to ensure that all aspects of safety in relation to nuclear facilities are understood. To achieve this goal, regulators must continue improving their communication strategies, and the implementation of such strategies.

International cooperation for continuous safety enhancement

International cooperation provides a forum for regulators to work together to share and analyse data and experiences, gain consensus, and develop approaches that can be applied within each country’s regulatory process. International cooperation also provides a platform for peer regulators to encourage vigilance in ensuring nuclear power plant safety and avoiding the complacency that contributed to the accident at Fukushima.

Regulatory authorities from NEA member countries are working together internationally to share information and actions taken to improve their regulatory frameworks and power plant safety. The NEA provides an effective forum for cooperation in both medium- and long-term issues in its specific task groups, working parties and expert groups, as well as through joint international safety research projects.