Kansai opts to retire older Ohi units

Kansai Electric Power Company has today announced that it will not seek permission to restart units 1 and 2 of its Ohi nuclear power plant in Japan's Fukui Prefecture. The company will now apply to decommission the two 1175 MWe pressurised water reactors, which are approaching 40 years old.

Kansai Electric Power Company has today announced that it will not seek permission to restart units 1 and 2 of its Ohi nuclear power plant in Japan's Fukui Prefecture. The company will now apply to decommission the two 1175 MWe pressurised water reactors, which are approaching 40 years old.

Ohi units 1 and 2 (Image: Kansai)

The company said it made the decision at an extraordinary board meeting today. It has informed Ohi town and Fukui Prefecture of its decision to decommission the units, which began operating in March 1979 and December 1979, respectively.

"We will go through the various procedures to decommission units 1 and 2 of the Ohi plant," Kansai said in a statement, "and proceed with decommissioning, making safety a top priority." These procedures include applying for regulatory approval to decommission the units.

Kansai President Shigeki Iwane was cited by the Kyodo news agency as telling Fukui Governor Issei Nishikawa, "The decision we made is the result of giving priority to securing the safety and quality [of the reactors] after considering measures to meet new safety standards."

Ohi 1 and 2 - which have been offline since July 2011 and December 2011, respectively - are the only ones in Japan to feature ice condenser emergency cooling systems. These systems employ blocks of ice in a basket installed around the containment vessel to rapidly cool steam generated to reduce pressure in the event of an accident.

Kansai said that to comply with new safety standards, the walls of the containment buildings of Ohi 1 and 2 would had to have been thickened. However, reinforcement of the walls would have narrowed the space between the containment vessel and the wall of the containment building.

"It will be difficult to safely and securely carry out periodical inspection, equipment inspection and maintenance work during operation, and rapid repair when needed," the company said. "We have discussed it from a technical point of view, however, we have not been able to find an effective method."

Kansai had estimated it would have cost some JPY830 billion ($7.3 billion) to make safety upgrades for the units to meet the required standards.

Ohi 1 and 2 are the first reactors with capacities over 1000 MWe to be decommissioned in Japan following the accident at the Fukushima Daiichi plant in March 2011.

Five smaller Japanese reactors - Genkai 1, Mihama 1 and 2, Shimane 1 and Tsuruga 1 - were declared for decommissioning in mid-March 2015 following the introduction of an accounting-related system earlier that month to determine which units should not be restarted.

Under revised regulations that came into force in July 2013 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. The owners of the five units decided to shut them after an assessment of the work needed to ensure the units meet the new safety requirements.

Shikoku Electric Power Company announced in March 2016 that it had decided not to restart unit 1 of its Ikata plant. Last December, the government also formally announced its decision to decommission the idled Monju prototype fast breeder reactor.

Following the shutdown of all of Japan's reactors after the Fukushima Daiichi accident, Kansai was given permission to resume operation of the newer units 3 and 4 of the Ohi plant in August 2012. However, the two 1180 MWe pressurised water reactors were taken offline again for inspections in September 2013. The governor of Japan's Fukui Prefecture last month approved the restart of those units. The utility reportedly plans to restart both units by mid-2018.

Researched and written
by World Nuclear News