Tsuruga 2 sits on active fault, NRA concludes

26 March 2015

The restart of unit 2 of the Tsuruga nuclear power plant in Japan's Fukui prefecture has been thrown into doubt after the Nuclear Regulation Authority (NRA) accepted a report compiled by a panel of experts that concluded the unit sits upon an active fault line. However, plant owner Japan Atomic Power Company (JAPC) says it still plans to apply for safety checks in order to restart it.

Tsuruga 2 - 250 (JAIF)
Tsuruga 2 (Image: JAIF)

At a regular meeting of the NRA yesterday, the regulator's decision-making panel accepted the final evaluation report into a fault zone directly below the reactor building of Tsuruga unit 2. The report concluded that the fault is active and could cause an earthquake.

New regulatory standards announced in June 2013 prohibit reactor buildings and other important facilities being located above any active fault. The acceptance by the NRA that Tsuruga 2 sits upon such a fault suggests that the unit will not be restarted and will be decommissioned.

However, JAPC has objected to finalization of the evaluation report, claiming there were problems in the draft evaluation. The company said it will proceed with the filing of applications to the NRA for necessary permissions to restart the reactor.

The panel of experts conducted on-site investigations twice at Tsuruga 2 since 2012, focusing on the activity of a fault running directly under the reactor building. The NRA made an evaluation of fault in May 2013 saying it was active. However, after receiving a report from JAPC in July 2013 on its own investigation into the fault, the NRA has conducted on-site investigations and held additional evaluation meetings. JAPC has repeatedly disagreed with the NRA on how its evaluation was carried out.

On 24 March - the day before yesterday's meeting - JAPC asked the NRA to only "finalize an evaluation report after sufficient discussions on a scientific, technical basis."

NRA chairman Shunichi Tanaka said the regulator would refer to the evaluation result in its examination of JAPC's applications to restart Tsuruga 2, making the restart of the 1160 MWe pressurized water reactor appear unlikely.

Higashidori fault

Also at yesterday's meeting, the panel said that it has yet to reach a consensus on whether a fault below unit 1 of Tohoku Electric Power Company's Higashidori plant in Aomori Prefecture is active.

Tohoku applied to the NRA for safety checks at the 1100 MWe boiling water reactor in June 2014. However, the regulator has suspended its examination of that application until the panel came to a conclusion.

On-site investigations have been carried out four times at Higashidori 1, but evaluation of several faults within the site encountered significant difficulties. While the panel has agreed that the two main faults under the site are active, it has yet to agree on whether the fault under important facilities at unit 1 could cause an earthquake.

NRA commissioner Akira Ishiwatari said, "It is very difficult to judge the situation. This is not a matter on which we can have an answer soon."

Researched and written
by World Nuclear News