A five-member team of the Nuclear Regulatory Authority decided Nov. 10 that there is a strong possibility that a “crush zone” of small rocks and sediment running beneath the No. 2 reactor of Japan Atomic Power Co.’s Tsuruga nuclear power plant is an active fault. The team’s conclusion is based on a two-day on-site geological survey as well as examination of data provided by the operator of the nuclear power plant.

On the basis of the team’s decision, Mr. Shunichi Tanaka, head of the NRA, said, “At this point, we cannot conduct safety checks to clear the restart of the Tsuruga reactors.”

The decision means that it has become extremely difficult for Japan Atomic Power to restart the No. 2 reactor as well as the plant’s No. 1 reactor, which is near the No. 2 reactor. The No. 1 reactor, which started commercial operation in March 1970, is Japan’s oldest commercial reactor. The logical step under this situation should be to decommission both reactors.

The NRA plans to carry out geological surveys of six nuclear power plants. Its most recent decision reinforces the case for having seismological and geological experts check all of Japan’s nuclear power plants, including Kansai Electric Power Co.’s Oi nuclear power plant in Fukui Prefecture, whose Nos. 3 and 4 reactors were restarted last summer, and Tohoku Electric Power Co.’s Higashidori nuclear power plant, which also has crush zones running under it.

Although Japan is prone to quakes, a number of nuclear power plants were allowed to be built at a time when seismological and geological knowledge — especially with regard to fault lines —was far less developed than it is now. Once the location of a nuclear plant was chosen, one reactor after another was built on the same site. After the reactors were built, the most up-to-date scientific knowledge was not fully reflected in the safety checks of reactors in operation. Thus there is a very real possibility that some nuclear power plants are situated near or above active faults whose existence was not known in the past.

The crush zone beneath the Tsuruga nuclear power plant’s No. 2 reactor, which is called D-1, branches out from the Urazoko fault, an active fault located about 250 meters from the reactor buildings.

Japan Atomic Power plans to build two new reactors only about 800 meters from the Urazoko fault. Three crush zones run beneath the site.

Constructing reactors at such a seismically unstable location is reckless and defies common sense. The government’s safety check guidelines prohibit building reactors and the facilities essential to their safe operation above active faults. The NRA should subject the nuclear power company’s new construction plan to the strictest scientific scrutiny to determine if the location is safe.

In the past, the safety evaluation of geological faults near nuclear power stations was largely left to the operators. The NRA team’s decision shows that the safety evaluation by operators was slipshod.

The Nuclear and Industrial Safety Agency and the Nuclear Safety Commission, which have allowed nuclear power plants to operate despite warnings from seismologists, bear a grave responsibility for the current situation. It is important to determine what these bodies did during their safety checks.

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