Japan’s Kansai Electric Power Co announced that safety improvement measures had been completed to enable extended operation for an additional 20 years of Mihama 3 and Takahama 1, both in Fukui Prefecture. Safety improvement measure were also underway for Takahama 2.
Mihama 3 will be 44 years old in December and Takahama 1 will be 46 years old in November. These are two of four ageing reactors authorised by the Nuclear Regulation Authority (NRA) to operate beyond the limit of 40 years, which the government introduced after the 2011 Fukushima accident.
Kansai plans to bring Mihama 3 back online in January 2021 and Takahama 1 in March, provided it receives approval from local governments. However, following a bribery scandal that was revealed last year, the head of Takahama Town said Kansai needs to improve corporate governance before the town can accept its plans.
In June 2016, Takahama 1 and 2 - both 780MWe pressurised water reactors (PWRs) were the first units to be granted a licence extension beyond the 40 years stipulated in the revised regulations. The units began operating in 1974 and 1975, respectively. In November 2016, NRA approved an extension to the operating period for Mihama 3, a 780MWe PWR, which began commercial operation in 1976.
Kansai has reinforced the concrete wall surrounding the containment vessels of Takahama 1&2 and has also installed secondary domes. Fire protection has been improved by replacing fire-resistant cabling, installing fire protection sheeting, and installing additional fire detectors and fire extinguishing facilities. The central control panels of both units have also been replaced. The refuelling water tank has been replaced and is now protected by an anti-tornado wall. The seawater intake facility at Takahama 2 is being relocated by excavating a new tunnel in the bedrock, and it will also be surrounded by an anti-tornado wall.
At Mihama 3 work has centred on improving seismic resistance. Kansai has reinforced the used fuel storage pool, replacing its fuel assembly rack. The internal structure of the reactor core has been replaced and seismic resistance of the reactor containment vessel improved. Fire protection has been improved, with the installation of fire-resistant cabling, fire protection panels, fire detectors, and new fire extinguishing equipment. A new, higher tidal barrier has been constructed.
Photo: Mihama nuclear plant (Alpsdake - Own work, used under CC BY-SA 4.0 )