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On-site survey at Higashidori

December 14, 2012


Team: Fault at nuclear plant may be active



Japan's nuclear regulator says that a nuclear power plant in northern Japan may be sitting on active faults.

Nuclear Regulation Authority official Kunihiko Shimazaki and 4 experts concluded their 2-day inspection at the Higashidori plant in Aomori Prefecture on Friday.

They scraped and washed the ground surface to see how far 2 faults in the compound extend.

Plant operator Tohoku Electric Power Company has argued that the shift in the strata was formed after soil in the ground absorbed water, and that it was not the result of seismic activity.

The experts say they cannot deny the possibility that the 2 faults are active, and that they can reach a conclusion without additional surveys.

Shimazaki says everyone on the team shares the same view and that they will discuss the matter next Thursday.

The experts also call for inspections on faults in and off Shimokita Peninsula, where the Higashidori plant and other nuclear facilities are located.

Tohoku Electric says the faults are not located directly beneath the reactor or other key facilities at Higashidori.

But if the nuclear regulator determines that the faults are active, the operator will have to review its earthquake-resistance measures and possibly close the plant.

The plant has been offline for regular safety checks.

NRA starts survey of Higashidori crush zones



A Nuclear Regulation Authority expert team on Thursday launched an on-site survey to ascertain whether the crush zones running below Tohoku Electric Power Co.'s Higashidori nuclear power plant in Aomori Prefecture are active faults.

During the two-day survey, the five-member team of experts, including NRA Acting Chairman Kunihiko Shimazaki, will check such sites as the trenches excavated by Tohoku Electric for their own surveys.

Next Thursday, the experts will hold an evaluation meeting to discuss their findings.

This is the third on-site survey to be conducted by the NRA. Earlier, they inspected Kansai Electric Power Co.'s Oi nuclear power plant and Japan Atomic Power Co.'s Tsuruga nuclear plant, both in Fukui Prefecture.

The crush zones running below the Higashidori power plant are considered by some experts as being at risk of moving in tandem with a main active fault.

Tohoku Electric has stated, "There is no active fault nearby."

The crush zones are away from the nuclear reactor. If they are judged to be active, however, there must be a main active fault nearby. This will prompt experts to fundamentally review the quake-resistance of the plant, while making it unlikely the plant will get approval to resume operations.

The team of experts will examine four crush zones south of the nuclear reactor building. They will inspect the trenches, which the power company excavated earlier, to observe the stratum of the crush zones, while checking geological samples collected earlier.

At a hearing held before the Great East Japan Earthquake last March by the now-defunct Nuclear and Industrial Safety Agency, experts pointed out that these crush zones might be active faults.

Tohoku Electric asserts they are the crush zones created not by earthquakes, but by a rise in groundwater levels.

If the crush zones are found to be at risk of moving in tandem with a main active fault, the question arises of where the main active fault is located.

A leading candidate is a peripheral fault on the continental shelf, running along the seabed about 7 kilometers east of the Higashidori plant.

Tohoku Electric has said the fault, which runs north and south for more than 80 kilometers, is not active.

Japan Nuclear Fuel Ltd.'s Rokkasho reprocessing plant and the Electric Power Development Co.'s Oma nuclear power plant, currently under construction, are near the peripheral fault. It is likely experts will discuss the quake-resistance of these two plants.




December 13, 2012


Survey starts on faults at Higashidori plant





Inspectors from Japan's Nuclear Regulation Authority have started an on-site survey into possible active faults under the Higashidori nuclear plant in Aomori Prefecture, northeastern Japan.

Regulation Authority official Kunihiko Shimazaki and 4 experts began the 2-day assessment on Thursday.

They observed cross-sections of faults found in trenches dug at the southern part of the plant compound.
Along a fault known as "s-19", the ground has shifted 90 centimeters.

Officials from plant operator Tohoku Electric Power Company say the movement is due to swelling of the strata from water absorption, not seismic activity.

But experts taking part in the survey doubt the utility's explanation. They say it is full of contradictions and they need more data.

The experts will meet in Tokyo on Thursday next week to present their assessment of the 2-day survey.

This is the NRA's third on-site assessment, following studies at the Ohi and Tsuruga plants, both in Fukui Prefecture on the Sea of Japan coast.

An NRA expert panel concluded earlier this week that a fault beneath the Tsuruga plant is likely to be active. The future of the plant is yet to be decided.

If the current Higashidori survey concludes that fissures in the compound are active, the plant may never be restarted. Government guidelines do not allow installation of key nuclear plant facilities above active faults.

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