10 Years of Fukushima Part 5: Lessons Learned

09.03.2021
© IAEA
Our five-part series "10 Years of Fukushima" looks at the nuclear accident in Japan from different perspectives. This week we present the lessons learned and consequences that the accident has had for nuclear power plant operation and supervision, both nationally and internationally.

The accident at the Fukushima Daiichi nuclear power plant caused the safety of nuclear power plants to be reviewed at national and international level and led to increased safety requirements worldwide. 

Germany: "Stress test", Information Notice, and new regulations

German stress test. A few days already after the disaster at Fukushima, the Federal Ministry for the Environment commissioned the Reactor Safety Commission (RSK) to subject all German nuclear power plants to a safety review - also known as a "stress test". The aim of this review was to assess the robustness of the plants against impacts or events that go beyond the original design. Robustness in this context means the ability of a plant to remain in a safe condition even under such beyond-design conditions.

The RSK then developed a catalogue of requirements that included scenarios that have a great influence on vital functions to maintain the safety of a nuclear power plant. These included natural hazards (e.g. earthquakes, floods) and events caused by civilisation (e.g. aircraft crash, terrorist attacks). Also included were event-independent scenarios, such as a prolonged power supply failure, as well as events that make it difficult to implement emergency measures (e.g. increased radiation exposure after a nuclear meltdown or destruction of safety-relevant infrastructure). However, since the scenarios considered were beyond the usual load assumptions of the nuclear rules and regulations, the RSK could not fall back on the criteria specified there. Therefore, it developed new criteria that referred to the robustness of the plants.

The operators of all German nuclear power plants had to present in a report what influence the listed scenarios had on the safety of their plants. The objective was to prove whether and to what extent the overriding protection goals – reactivity control, fuel cooling and limitation of the release of radioactive materials – could be met. The RSK evaluated the reports of the plant operators. The necessary inspections were organised by GRS on behalf of the RSK.

The RSK published its findings in a statement  on 16 May 2011. It came to the conclusion that German plants – compared to the nuclear power plant at Fukushima – had taken better precautions against events such as power failures and floods. To date, the RSK has published several statements and recommendations on this topic. 

Information Notice. In the course of the stress tests, the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety commissioned GRS to prepare an Information Notice on the Fukushima accident. GRS always prepares such Information Notices when an event of safety significance occurs in a nuclear power plant in Germany or abroad. GRS investigates whether the event can be applied to other plants and, if necessary, derives appropriate recommendations.

The information notice on Fukushima contains eleven recommendations on technical and organisational measures to improve the management of beyond-design-basis events. These include, for example, ensuring the power supply for at least ten hours by means of an additional emergency power generator, an autonomous auxiliary cooling water supply that is independent of the existing cooling water intake, or additional equipment for cooling the spent fuel pools in the event of a so-called station blackout, which is defined as the failure of a nuclear power plant's connection to the external power supply. 

National Action Plan. All European countries were required to draw up a National Action Plan after the accident at Fukushima. The Federal Ministry for the Environment published its national "Action Plan for the Implementation of Measures after the Reactor Accident at Fukushima" in December 2012. The plan had previously been coordinated with the nuclear authorities of all German Länder and the operators of the German nuclear power plants. In addition to the recommendations of the Reactor Safety Commission and the Information Notices of GRS, the action plan also took into account the results of the European stress tests and the recommendations of the International Atomic Energy Agency (IAEA). 

The action plan contained 23 overarching recommendations for improving the safety of nuclear installations. The translation of the recommendations into concrete measures – such as technical retrofitting – was carried out for each individual plant. In the course of the National Action Plan, amongst others the preventive emergency equipment was optimised, the technical prerequisites for extending the direct-current supply in the beyond-design-basis area were created, and mobile diesel generators were provided to restore the three-phase current supply in case of an emergency. In addition, each plant received a manual with mitigative emergency measures as an extension of the existing emergency manuals. A review by the European Nuclear Safety Regulators Group (ENSREG) was completed in 2015 with a positive result.

National nuclear regulations. The findings from the analysis of the accident were also incorporated into the national nuclear regulations. As early as in 2012, various points were added to the Safety Requirements for Nuclear Power Plants, including the requirement for a diverse heat sink, increasing the capacity of the battery-supported DC power supply, more stringent requirements for accident monitoring systems, and extensive requirements for the control of natural and man-made hazards.

Europe: Stress test, EURATOM Directive and WENRA safety requirements

European stress test. In 2011, the then European Union Energy Commissioner Günther Öttinger ordered stress tests for all 143 nuclear power plants in Europe. The European Nuclear Safety Regulators Group (ENSREG) defined the scope of the tests. Similar to the national stress test of the Reactor Safety Commission, the countries had to present the safety of their nuclear power plants for various beyond-design-basis events. The results were published by the supervisory authorities of the Länder in the form of a report. The reports were subjected to a peer review by experts and specific recommendations were made. ENSREG published all essential recommendations and suggestions in its summary "Compilation of Recommendations and Suggestions from the Review of the European Stress Test". 

Directive 2014/87/EURATOM. The European Council anchored the lessons learned in Directive 2014/87/EURATOM in 2014. Among other things, it stipulates the strengthening of the national supervisory authorities, the anchoring of the "Defence in Depth" concept, the performance of a periodic safety review at least every ten years, and the performance of a thematic peer review at European level every six years.

WENRA Safety Reference Levels. In the same year, the Western European Nuclear Regulators Association (WENRA) – an independent network of European regulatory authorities – also revised its Safety Reference Levels for nuclear power plants on the basis of the new findings from Fukushima. Among other things, the requirement to consider natural hazards beyond the design limits was added. The requirements for preventive and mitigative measures and equipment for the control of beyond-design-basis accidents were also fundamentally revised.

International: IAEA Action Plan, CNS Special Conference, Vienna Declaration

Action Plan on Nuclear Safety. Internationally, too, the accident at Fukushima led to revisions of safety standards and a variety of follow-up measures for nuclear power plants. In 2011, the International Atomic Energy Agency (IAEA) drew up an action plan to improve the safety of nuclear power plants worldwide. The twelve overarching goals of the "IAEA Action Plan on Nuclear Safety" include e.g. the timely assessment of the protection of nuclear power plants against beyond-design-basis natural hazards, the improvement of emergency preparedness as well as ensuring independent and effective state supervision. 

Special conference of the Convention on Nuclear Safety. On the occasion of the nuclear disaster at Fukushima, the IAEA organised a special conference in summer 2012 within the framework of the international Convention on Nuclear Safety (CNS). In advance, all participating countries had to submit a national report describing the safety of their nuclear power plants. The reports were discussed at the conference. In addition to plant-specific recommendations – similar to those from the stress tests – generic recommendations were developed with regard to organisational factors, off-site emergency protection, and international cooperation. GRS supported the Federal Ministry for the Environment in the preparation of the German report for the CNS special conference on Fukushima, the evaluation of the national reports of other participating countries, and during the conference itself.

Vienna Declaration on Nuclear Safety. Almost four years after the events at Fukushima, the States Party to the Convention on Nuclear Safety adopted the Vienna Declaration on Nuclear Safety in 2015. By this joint declaration, the States Party commit to the following three principles of nuclear safety: 

  1. New nuclear power plants must be planned and built in such a way that severe accidents are prevented. In the event of a severe accident with possible releases of radionuclides, there must be no long-term contamination outside the plant. Sufficient time must be available for protective measures of off-site emergency response.
  2. For existing nuclear power plants, safety must be regularly reviewed and improved.
  3. National regulatory frameworks should ensure these objectives and must take into account the Safety Standards of the IAEA and the Review Meetings of the Convention on Nuclear Safety (CNS).
IAEA International Nuclear Safety Standards. Subsequently, the IAEA updated five of its general and specific safety requirements ("Safety Standards") on the regulatory framework, safety demonstration, site selection, and design and operation of nuclear power plants, thus implementing the lessons learned from the accident at the Fukushima Daiichi nuclear power plant. GRS supported the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) in commenting on drafts of the Safety Standards and collected and compiled all comments from expert organisations, industry, and the general public. 

Japan: New nuclear supervision and safety reviews

In Japan, the supervisory authority ordered the gradual shutdown of all 17 Japanese nuclear power plants with a total of 51 reactor units after the accident. This situation lasted for almost two years. Only after extensive safety checks and retrofitting did the first two nuclear power plant units generate electricity again in 2015. 

The Japanese government was initially occupied with investigating the sequence of events and the causes of the accident. Two government investigation commissions came to the conclusion that the catastrophe in its origin, course and severity was due to a large number of technical and organisational deficiencies. On the one hand, the Fukushima nuclear power plant was insufficiently resistant to beyond-design-basis events such as tsunamis. Secondly, there was a lack of appropriate accident management measures to stop any developing accidents or to limit their effects. 

Furthermore, the two commissions were able to uncover a fundamental problem: a deficient safety culture on the part of the operator TEPCO and insufficient supervision by the responsible government agencies, caused by a lack of distance and conflicts of interest between the promotion and control of nuclear energy use. The Japanese nuclear regulatory authority NISA was subsequently spun off from the Ministry of Economy and replaced in 2012 by the Nuclear Regulation Authority, which is independent of the government. 

 Find out more

 >> Statement by the Reactor Safety Commission (RSK) (German only)

 >> Final report of ENSREG 

>> Information Notice of GRS (German only)