An International Atomic Energy Agency (IAEA Safety Aspects of Long Term Operation (SALTO) team has completed a review of long term operational safety of unit 3 at the Mihama NPP in Japan. The review mission was requested by the plant’s operator, Kansai Electric Power Company.

Unit 3 started its commercial operation on 1 December 1976. It underwent an outage of approximately 10 years after the Fukushima-Daiichi NPP accident in March 2011. In 2015, Kansai Electric applied to extend the operational period of Mihama 3 from 40 to 60 years until November 2036. In 2016, Japan’s Nuclear Regulation Authority (NRA) approved the extension. In 2021, unit 3 was restarted and began its long-term operation.

The SALTO team assessed the strategy and key elements for safe long-term operation (LTO) of NPPs based on the IAEA safety standards. During the ten-day mission, the team reviewed the plant’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 US as well as three observers from Finland and South Korea, and two IAEA staff members. The team had in depth discussions with staff from the Mihama NPP and conducted plant walkdowns during the review.

The team observed that Kansai Electric 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 identified good performances, including:

  • The plant has developed and effectively implemented a comprehensive methodology for identification and management of design obsolescence. The use of this methodology constitutes a powerful tool to proactively address obsolescence issues and identify safety improvements.
  • The plant has 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.
  • The plant 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 to further improve safe LTO; the most significant are the following:

  • The plant should further develop and implement the LTO programme.
  • The plant should fully develop and complete the Ageing Management Review process for mechanical, electrical, and instrumentation & control (I&C) components and civil structures.
  • The plant should improve the programmes designed to confirm the resistance of components to harsh conditions, a so-called equipment qualification programme.

The plant management expressed a determination to address the areas identified for improvement and to continue its cooperation with the IAEA. Kazutaka Tsuru, the General Manager of Mihama Power Station said Kansai Electric is wholly committed to improving upon the topics recommended and suggested by the SALTO team. “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. I would like to express my appreciation again for the dedicated support the IAEA team provided for the review.”

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, NRA and the Japanese Government after comments are addressed.

Image: SALTO Team Leader Martin Marchena (second from right) in discussion with staff at the Mihama nuclear power plant (courtesy of KEPCO)