Under revised regulations which came into force in July 2013, Japanese reactors have a nominal operating period of 40 years. Extensions can be granted once only and limited to a maximum of 20 years, contingent on exacting safety requirements.
In November 2016, Japan's Nuclear Regulation Authority (NRA) approved an extension to the operating period for Kansai's Mihama unit 3, a 780 MWe pressurised water reactor that entered commercial operation in 1976. The NRA's decision cleared the unit to operate until 2036. Mihama 3 was the third Japanese unit to be granted a licence extension enabling it to operate beyond 40 years under the revised regulations, following Kansai's Takahama 1 and 2 which received NRA approval in June 2016.
Mihama 3 was restarted in June 2021 after having been idle since May 2011 following the accident at the Fukushima Daiichi plant two months earlier. It became the first Japanese power reactor to operate beyond 40 years.
The International Atomic Energy Agency (IAEA) has now completed a ten-day Safety Aspects of Long-Term Operation (SALTO) mission to Mihama 3, carried out at Kansai's request.
A SALTO peer review is a comprehensive safety review addressing strategy and key elements for the safe long-term operation of nuclear power plants. SALTO missions complement IAEA Operational Safety Review Team (OSART) missions which are designed as a review of programmes and activities essential to operational safety. SALTO peer reviews can be carried out at any time during the lifetime of a nuclear power plant, although according to the IAEA the most suitable time lies within the last ten years of the plant's originally foreseen operating period. SALTO and OSART reviews are carried out at the request of the IAEA member country in which the review is to take place.
The team reviewed Mahama 3's preparedness, organisation and programmes for safe LTO. The mission was conducted by an 11-person team comprising experts from the Czech Republic, France, Sweden, the UK and the USA, as well as three observers from Finland and South Korea, and two IAEA staff members.
The team identified good performances, including that the plant has developed and effectively implemented a comprehensive methodology for identification and management of design obsolescence. The plant has also participated in benchmarking efforts related to ageing management of the steel containment and containment pressure testing and uses these benchmarking efforts to enhance the ageing management activities of the civil structures. In addition, it has put in place an effective mentoring programme using retired staff as mentors for new and current staff to develop their competencies and skills.
The team also provided recommendations and suggestions, including that the plant should further develop and implement its LTO programme and should fully develop and complete the ageing management review process for mechanical, electrical, and instrumentation and control components and civil structures. It also said the plant should improve its so-called equipment qualification programme, designed to confirm the resistance of components to harsh conditions.
"The team observed that Kansai is implementing measures for safe LTO in a timely manner and the staff at the plant are professional, open and receptive to proposals for improvement," said team leader and IAEA Nuclear Safety Officer Martin Marchena. "Some ageing management and LTO activities already meet IAEA safety standards. We encourage the plant to address the review findings and implement all remaining activities for safe LTO as planned."
The team provided a draft report to the plant management and to the NRA at the end of the mission. The plant management and the NRA will have an opportunity to make factual comments on the draft. A final report will be submitted to the plant management, the NRA and the Japanese government after comments are addressed.
"Kansai is wholly committed to improving upon the topics recommended and suggested through the SALTO review," said Kazutaka Tsuru, the general manager of the Mihama plant. "As a pioneer in Japan's nuclear power generation sector, we also intend to roll out the improvements to domestic nuclear power stations and contribute to maintaining and developing the country's nuclear power generation. Harnessing the knowledge obtained from the review, we hope to make efforts to achieve higher standards with the support of IAEA members."
