NRA not quite sure - Further investigation needed

December 31, 2012

Oi N-plant fault survey may be prolonged

http://www.yomiuri.co.jp/dy/national/T121230002382.htm

OI, Fukui (Jiji Press)--The Nuclear Regulation Authority's on-site survey of the Oi nuclear power plant may be prolonged, as scientists who completed Saturday's inspection are unlikely to reach an immediate conclusion on whether there is an active fault.

Most members of a survey team commissioned by the authority stopped short of making a clear judgment on whether a crush zone under the plant site is an active fault after a second round of surveying at the Kansai Electric Power Co. plant in the town of Oi.

NRA deputy chief Kunihiko Shimazaki, who led the team, indicated at a news conference that it may take time to draw a conclusion. The judgment on the Oi plant is more difficult than that on Japan Atomic Power Co.'s Tsuruga nuclear power plant in Fukui Prefecture, he said.

After a single on-site survey in early December, experts agreed a crush zone running under the Tsuruga plant was highly likely to be an active fault.

If the NRA concludes there is an active fault under the Oi plant, its No. 3 and No. 4 reactors--the only reactors currently in operation in Japan--would face a possible shutdown.

The Oi reactors were brought back online in July. The nation's other 50 reactors remain idled in the wake of the accident at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear power plant, which was crippled by the March 2011 earthquake and tsunami.

On Saturday, the second day of the latest survey at the Oi plant, team members checked trenches dug for research, including one on the north side, where displacement was found in the geological layers.

Four of the five team members said it was possible there was an active fault running beneath the plant.

However, Ritsumeikan University Prof. Atsumasa Okada said the displacement in the northern trench looked different from active faults he had seen before.

Shimazaki said Okada's view did not necessarily provide a basis for denying the existence of an active fault.

At a meeting to be held early next year to examine the survey's findings, team members are expected to focus on reasons for the displacement.

As for the F-6 crush zone, which is believed to run under critical facilities of the Oi plant, they will have difficulty reaching a conclusion as a reversal in Kansai Electric's explanations has made it difficult to determine its exact location

December 30, 2012

Japanese experts still divided over status of allegedly active fault beneath Oi nuclear power plant

Kyodo

http://www.japantimes.co.jp/text/nn20121230a4.html

A team of experts examining the geological formation under Japan's sole operating nuclear power plant remained split over whether an active fault runs beneath it after completing their second field survey Saturday.

Four of the group's five members, including Kunihiko Shimazaki, head of the investigation team and a commissioner of the Nuclear Regulation Authority, indicated they could not rule out the possibility that an active fault runs underneath two restarted reactors at Kansai Electric Power Co.'s Oi power plant in Fukui Prefecture.

But team member and Ritsumeikan University professor Atsumasa Okada said that what the experts had observed "can be explained as a landslide," noting the rock formation differs from active faults he has previously seen.

Kansai Electric denies that an active fault exists under the Oi complex.

The outcome of the inspection is under the spotlight since the government approved the restart of reactors 3 and 4 at the Oi plant in July, making them the first atomic units to resume operations since the triple meltdown crisis at the Fukushima No. 1 plant last year saw all of the nation's reactors halted for safety checks.

In Saturday's survey, the team checked a test trench dug outward from the fracture zone of the F-6 fault, which is suspected of being active, as well as another test trench and the coastal area of the compound. The power station was built on the shores of the Sea of Japan.

While the team will hold an evaluation session early in the new year, its members are seen as unlikely to reach a unified conclusion anytime soon. A large amount of data were gathered Saturday, and the five experts all said they needed time to analyze them thoroughly before reaching a conclusion.

Shimazaki, the group leader, is meanwhile calling for more boring to be conducted in the southern part of the Oi complex under a new survey, which could further delay the team's final report.

If the F-6 fault — believed to run below the emergency water intake channel of the fully operational No. 3 and 4 reactors — is deemed to be active by the group, the NRA plans to order Kansai Electric to immediately take both units offline.

See also :

Researchers still split over fault assessment at Oi nuclear plant

http://mainichi.jp/english/english/newsselect/news/20121230p2g00m0dm058000c.html

TOKYO (Kyodo) -- Experts investigating the geological formation under Japan's sole operating nuclear power plant remained split over assessing whether it is an active fault or not after completing their second field survey.

But another member, Ritsumeikan University Professor Atsumasa Okada, said what they saw "can be explained as a landslide," adding it is different from active faults he has seen so far.

The outcome of the inspection has come under the spotlight as the government approved the restart of the plant reactors' operations earlier this year even after the nuclear crisis at Fukushima Daiichi power plant triggered by the quake and tsunami last year.

Kansai Electric denies the formation is an active fault.

While the team will hold an evaluation session early in the New Year, they are unlikely to reach a unified conclusion then or any time soon as Shimazaki is also calling for another bore survey in the southern part of the premises of the Oi plant.

In the Saturday survey, the team checked the test trench dug outward from the F-6 fault fracture zone suspected of being an active fault as well as another test trench and landscapes along the ocean.

If F-6, believed to be running underneath the emergency water intake channel of the operating No.3 and No. 4 reactors, is decided to be an active fault, the NRA plans to demand the utility suspend the operations of the reactors.

December 29, 2012

Experts yet to reach conclusion on crush zone

http://www3.nhk.or.jp/daily/english/20121229_29.html

Experts from Japan's nuclear regulatory body are trying to determine whether there are any active faults running underneath the country's only online nuclear power plant.

A Nuclear Regulation Authority team ended a 2-day survey at the Ohi plant in Fukui Prefecture on the Sea of Japan on Saturday.

The 5-member team, led by the regulatory body's commissioner Kunihiko Shimazaki, examined a recently dug trench in the northern part of the plant's premises.

The plant operator, Kansai Electric, says the fissures beneath the plant were caused by landslides and are not active faults. However, on the first-day of the survey, experts expressed doubt about that explanation.

The team concluded Saturday's survey with an inspection of another trench dug on a ridge running through the plant's premises that revealed a fault.

The discovery of the fracture last month has sparked disagreement.

Some experts say it resulted from landslides while others say it was caused by a large active fault.

The team failed to reach a consensus on Saturday.
It plans to meet again in the coming weeks to form an assessment based on the survey results.

Shimazaki says there are various data that need to be studied, and suggested that it will take longer than the assessment they made earlier this month on the Tsuruga plant in Fukui Prefecture. They determined that the faults underneath that plant are active.

The regulatory body will call on Kansai Electric to shut down the Ohi plant if the fissures beneath the facilities are confirmed to be an active fault.

The plant's Number 3 and 4 reactors resumed operation in July, the first to do so since the nuclear disaster in Fukushima last year.

Shimazaki says he wants to hold further discussions after more trenches are dug near the reactors in the next few months. Observers see his remarks as indicating that the survey may be prolonged.