Change quake preduction or not?

July 2, 2015

Nuclear watchdog threatens to abort screening of Mihama plant

http://mainichi.jp/english/english/newsselect/news/20150702p2a00m0na010000c.html

The Nuclear Regulation Authority (NRA) has threatened to terminate safety screenings for reactivating the Mihama nuclear power plant's No. 3 reactor if its operator, Kansai Electric Power Co. (KEPCO), fails to finalize a maximum seismic projection for the plant's premises by the end of August, it has been learned.

The nuclear watchdog announced the decision on July 1 over the plant's No. 3 reactor in Fukui Prefecture, whose operational life will reach the 40-year limit at the end of November next year. The move comes after KEPCO showed reluctance to raise the maximum earthquake ground motion for the plant site.

KEPCO is seeking to extend the operational life of the No. 3 reactor and filed for safety screenings in March. In order to bring about the extension, however, the utility will need to have inspections on the reactor completed by the end of November 2016, including anti-dilapidation measures.

At a regular meeting on July 1, the NRA estimated that it will take around 15 months from finalizing basic ground motion -- which serves as seismic design standards for reactors -- until screenings on other matters are completed at the plant, meaning that the utility must finalize the basic earthquake ground motion by the end of August.

Basic earthquake ground motion greatly varies depending on the predicted depths of an epicenter. KEPCO estimates that a quake whose epicenter's upper edge is four kilometers deep could hit the Mihama plant, while setting the figure at three kilometers deep for the nearby Takahama and Oi nuclear stations, respectively. The NRA has called on KEPCO to review the figure for the Mihama plant to make it on par with those for the other two plants.

If KEPCO reviews and finalizes basic ground motion for the Mihama facility, it will require additional seismic reinforcement work, possibly raising the costs for safety measures. If the utility sticks to the four-kilometer-deep epicenter scenario, however, it will not be able to finalize basic ground motion by the deadline, possibly leading to the decommissioning of the reactor.

During a July 1 press briefing, NRA Chairman Shunichi Tanaka said, "(If KEPCO fails to finalize basic ground motion by the end of August) we must consider measures including suspension of screenings. The operator (KEPCO) needs to be aware of that."

A senior KEPCO official told the Mainichi Shimbun, "We will consider whether to change our quake predictions before the next meeting for safety screenings is convened."

The upper limit of a reactor's operational life is set at 40 years, but it can be extended by up to 20 years only once.