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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Oi Fault : Active or not ?

November 2, 2012

Nuclear regulator researches Ohi plant



Japan's Nuclear Regulation Authority has surveyed the country's only operating nuclear power plant to determine whether a seam under the facility is an active fault.

The authority says it may ask the Ohi plant's operator -- Kansai Electric Power Company -- to suspend operations, depending on the survey results.

Its member Kunihiko Shimazaki and 4 other outside experts visited the plant on the Sea of Japan coast in Fukui Prefecture on Friday.

They were first briefed by Kansai Electric about what it has found in its own survey.

Later, the team took samples from under the northern part of the plant's premises.

In the afternoon, they examined a column of soil layers taken from ground in and around the seam to check its hardness and other properties.

After the inspection, Shimazaki said the team learned a lot and that the agency is to hold a meeting on Sunday to assess the results. He also said an additional survey may take place if necessary.

Nuclear plant operators in Japan are not allowed to build reactors or other facilities crucial for safe operation of reactors directly above active faults. The Ohi plant has a water channel above the seam to take in seawater for cooling reactors.

Kansai Electric submitted an interim report of its own survey to the agency on Wednesday. It says the fissure is not an active fault.

The regulator plans to conduct similar surveys at five other nuclear plants across Japan in the wake of the massive earthquake and tsunami in March last year. The disaster devastated the Fukushima Daiichi nuclear power plant in northeastern Japan.

Nov. 2, 2012 - Updated 10:24 UTC (19:24 JST)





Nuclear regulatory body starts studying disputed fault at Oi plant

Nuclear Regulation Authority Commissioner Kunihiko Shimazaki and other members of the government body examine layers of earth in a trench at the Oi Nuclear Power Plant in Oi, Fukui Prefecture, on Nov. 2. (Mainichi) 

Nuclear Regulation Authority Commissioner Kunihiko Shimazaki and other members of the government body examine layers of earth in a trench at the Oi Nuclear Power Plant in Oi, Fukui Prefecture, on Nov. 2. (Mainichi)

TOKYO (Kyodo) -- Japan's nuclear regulatory authority on Friday started a one-day investigation at Kansai Electric Power Co.'s Oi nuclear power plant in Fukui Prefecture to check whether a disputed fault running underneath it should be viewed as active.

Depending on the outcome of the investigation, the sole operating plant in the quake-prone country could be asked to shut down, just months after two of its reactors were allowed in July to restart having cleared a safety screening process carried out by the Nuclear Regulation Authority's predecessor.

It is the first time for the NRA to conduct an on-site inspection of a nuclear plant following its establishment in September.

At the government's request, Kansai Electric is further studying the F-6 fault, which runs north-south between the plant's Nos. 1-2 reactors and Nos. 3-4 reactors. But it has said that it has so far not found data suggesting movements in the last 120,000 to 130,000 years -- the current definition of an active fault in Japan.

The NRA, however, plans to make its own judgment based on Friday's investigation, which is being carried out by a team consisting of NRA commissioner Kunihiko Shimazaki and four other experts selected from outside the regulatory body.

The experts include Toyo University professor Mitsuhisa Watanabe, who has highlighted the risk posed by the F-6 fault, where a zone of crushed rocks has been found in bedrocks.

The shattered zone in question will not trigger an earthquake, but it is feared it could move together with active faults near the plants' premises and damage a water channel that would be used to take in seawater to cool reactors in the event of an emergency.

Utilities are not allowed to build reactors and other related facilities important for safe operation of reactors directly above active faults.

Prior to the investigation, NRA Chairman Shunichi Tanaka has said that, if the F-6 is determined to be an active fault, or strongly suspected to be, the authority would ask for the suspension of the currently operating Nos. 3 and 4 reactors.

Public concerns remain strong over the safety of nuclear power in the wake of the nuclear crisis at Tokyo Electric Power Co.'s Fukushima Daiichi plant last year, and the NRA is in the process of devising new safety standards for reactors.

The NRA-led investigation team is expected to meet Sunday to discuss the outcome of the on-site inspection.

The regulators also plan to implement similar investigations at five other nuclear facilities, including Hokuriku Electric Power Co.'s Shika plant in Ishikawa Prefecture and Kansai Electric's Mihama plant in Fukui.

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