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2012年10月20日 (土)

原発と活断層 公明正大な調査が求められる

The Yomiuri Shimbun (Oct. 20, 2012)
Fair probe necessary on faults under N-plants
原発と活断層 公明正大な調査が求められる(10月19日付・読売社説)

In November, the government's Nuclear Regulation Authority will begin on-the-spot investigations to confirm if there are any active faults immediately below nuclear power plants.

It is necessary to strictly check the safety of nuclear plants to prevent them from being directly hit by earthquakes.

The first to be probed will be Kansai Electric Power Co.'s Oi nuclear plant in Fukui Prefecture, whose reactors are the first and only ones to be reactivated since the Great East Japan Earthquake.

Earthquake expert Kunihiko Shimazaki, a delegate representing the NRA chairman, will visit the plant with four other experts on active faults. The NRA plans to conduct similar investigations at five other locations, including Hokuriku Electric Power Co.'s Shika nuclear plant in Ishikawa Prefecture.


Ground to get a second look

The six nuclear plants were believed to have no active faults beneath them when they were designed and built. But after last year's earthquake disaster, the now-defunct Nuclear and Industrial Safety Agency reexamined relevant materials from the time of those plants' design and construction, and found data that raised suspicion that active faults might exist below them.

It also has been found that power companies in their past investigations sometimes erred by considering separate faults as a single fault.

A powerful movement by an active fault beneath a nuclear plant could have unpredictable results, such as reactors being knocked askew or other key equipment getting damaged.

Some observers believe last year's massive earthquake has changed the geological conditions of the Japanese archipelago in ways that make active faults more susceptible to movement. The NRA's investigations are expected to closely examine such possibilities and dispel concerns associated with them.

The NRA has said it will ask power companies to halt the operations of nuclear reactors or decommission them if the existence of any active faults immediately below the plants is confirmed.

We consider it reasonable to strictly screen nuclear plants whose safety is questioned based on investigation results.


Clear judgments not easy

The problem is that even experts often assess active faults differently. There are usually many cracks and fractures in the bedrock and overlying strata. It is no easy task to determine to what extent they would cause intensive and dynamic movements in the future.

NRA Chairman Shunichi Tanaka said, "In scientific and technical terms, it's quite difficult to make a 'gray area' judgment [on whether a fault is active]."

But we think the authority should not be able to order the decommissioning of nuclear reactors based on vague evaluations.

The NRA should establish clear and uniform criteria for determining whether faults are active as soon as possible. If the authority demands that power companies decommission reactors in the absence of guiding standards, the utilities may take the matter to court.

For their part, power companies must not simply wait for the NRA's evaluations. They should not neglect to confirm the safety of their nuclear plants on their own.

It also has been found that power companies have failed to properly keep materials related to past explorations of subterranean conditions.

We want them to keep firmly in mind that they cannot escape responsibility if a nuclear disaster triggered by an earthquake occurs.

(From The Yomiuri Shimbun, Oct. 19, 2012)
(2012年10月19日01時30分  読売新聞)


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