Mihama plant: more data needed

December 9, 2013

Nuke authority seeks additional Mihama plant fault data from KEPCO

http://mainichi.jp/english/english/newsselect/news/20131209p2a00m0na008000c.html

A team of experts from the Nuclear Regulation Authority (NRA) wrapped up two-day on-site investigations on fault lines under the Mihama Nuclear Power Plant in Fukui Prefecture on Dec. 8, but stopped short of determining whether the fault lines are active or not, citing lack of information.

The NRA requested plant operator Kansai Electric Power Co. (KEPCO) to submit additional data on the fault lines, citing a shortage of information for the agency to reach a conclusion. If the fault lines are determined to be active, the plant likely faces decommissioning. KEPCO has heretofore maintained in its report that the fault lines are not active.

There are nine fracture zones under the nuclear plant's premises. Six of them run directly underneath the buildings for the No. 1 to 3 reactors. There is also a 15-kilometer active fault line running from north to south, called the "Shiraki-Nyu fault line," about one kilometer to the east. Some experts have pointed out the possibility of the fracture zones under the plant moving in tandem with the fault line.

The five-member research team, including NRA acting chairman Kunihiko Shimazaki, investigated the relationship between the fracture zones and the Shiraki-Nyu fault line by observing the geological formations between them on Dec. 8.

After the survey, Shimazaki said, "It's not that our investigations are over. We need a little more data before making a conclusion (over whether the fault lines are active)."

The NRA is demanding KEPCO submit the additional data before an evaluation meeting scheduled for the beginning of next year and will ask the utility to conduct additional surveys if necessary.

The Mihama plant's suspected active fault issue emerged during a review of fault lines on the plant's premises by the now-defunct Nuclear and Industrial Safety Agency under the Ministry of Economy, Trade and Industry in the wake of the March 2011 Great East Japan Earthquake and the ensuing Fukushima No. 1 Nuclear Power Plant disaster. Regulations forbid the construction of key nuclear plant structures directly above active fault lines.

December 09, 2013(Mainichi Japan)