Japan's Nuclear Regulation Authority has officially ruled that unit 2 of the Tsuruga nuclear power plant in Fukui prefecture cannot be restarted as it does not comply with regulatory safety standards.
New regulatory standards announced in June 2013 prohibit reactor buildings and other important facilities being located above any active fault.
On two occasions - in May 2013 and March 2015 - a Nuclear Regulation Authority (NRA) panel of experts concluded that an active fault lies under the Tsuruga 2 reactor building. However, owner Japan Atomic Power Company (JAPC) has maintained that its own analysis has shown that the fault is not active and does not extend under the unit. In November 2015 it applied to the NRA for a review to restart the operation of Tsuruga 2.
An NRA review team presented the results of their confirmation of the activity of the fault at a meeting on 31 May this year, and the continuity of the fault at a meeting on 26 July. The team concluded that the possibility of an active fault running directly underneath the reactor building "cannot be denied". The regulator adopted the team's draft screening report in August.
Following a public comment period, the NRA has now ruled that the unit does not comply with the regulatory safety standards and can therefore not be restarted. It marks the first instance that such a decision has been made under the new regulations.
NRA Chairman Shinsuke Yamanaka was quoted by Jiji Press as saying "it was a big decision", adding that the decision "is not different at all from those made so far, in that we conducted strict screening from scientific and technical standpoints".
In a statement, JAPC said it was "disappointed" with the NRA's decision. "It did not recognise that the activity and continuity of the K fault found in the D-1 trench on the site of Tsuruga nuclear power plant unit 2 are in conformity with the new regulatory standards," it said.
"We will work toward reapplying for permission to change the installation of Tsuruga nuclear power plant unit 2 and starting operation," the utility added. "We will specify the content of the additional investigation required for the application, taking into account the opinions of external experts."