Accordingly, in October 2021, Kyushu Electric began special inspections to ascertain the soundness of the reactor vessels and other facilities at Sendai-1 and -2, and filed applications with the NRA in October 2022 for permission to extend their operating lifetimes by 20 years.

At a regular meeting on November 1, the NRA’s Secretariat explained the examination results. Six items were specified as possible areas of major physical degradation, to be evaluated in an aging examination:

  1. low cycle fatigue
  2. neutron irradiation embrittlement of the reactor vessel
  3. Irradiation-induced stress corrosion cracking
  4. thermal aging of duplex stainless steel
  5. deterioration of cable insulation
  6. loss of strength of concrete structures

The results of the special inspections were evaluated, and it was then determined that conditions would remain compliant with standards during the period that operations would be extended.

After the enforcement of Japan’s New Regulatory Requirements for Commercial Nuclear Power Reactors in July 2013, Sendai-1 and -2 were the first to be restarted, in 2015. Operated continually at rated thermal output, they have performed well, with capacity factors reaching 107% during the winter months.

Six domestic NPPs in Japan have now been approved for operation beyond 40 years: Mihama-3 and Takahama-1 and -2, all owned and operated by the Kansai Electric Power Co. (Kansai EP)—all of which have been restarted—and the Tokai-2, owned and operated by the Japan Atomic Power Company (JAPC), along with the two Sendai units.

After the bundle of bills amending Japan’s energy-related laws—including the Electricity Business Law, which aims at creating an electricity supply system leading to the realization of a decarbonized society (the GX Decarbonization Power Supply Bill), and which the Diet passed on May 31, 2023—comes into force in June 2025, a nuclear operator will be required to make a technical evaluation of reactor deterioration at the 30th year of operation and every ten years thereafter, and issue a long-term facility management plan.