Recent reassessments of the safety of nuclear power plants leave little doubt that the risks posed by active faults, just like the risks of possible tsunami, were estimated in a shockingly sloppy manner.
The reassessments of the seismic hazards to individual nuclear facilities have raised suspicions that some nuclear power plants are sitting atop active faults, long cracks in the earth that can move and cause earthquakes.
Nuclear safety regulations prohibit the construction of important nuclear power facilities directly above active faults.
But experts now suspect that the Japan Atomic Power Co.’s Tsuruga nuclear power plant, Hokuriku Electric Power Co.’s Shika nuclear plant and Kansai Electric Power Co.’s Oi and Mihama plants may be located right above active faults.
The fresh seismic hazard analyses that led to the concerns were prompted by a major earthquake that struck southern parts of Fukushima Prefecture in April last year.
A fault that had been declared to be inactive by both the electric power company serving the area and the government actually moved along with other faults, making the quake bigger.
When experts took a fresh look at faults in various parts of the nation, they discovered many faults that were previously labeled inactive might actually be active.
Behind these developments are lax safety inspections of the locations of nuclear power plants in the past.
After studying the area around the Tsuruga nuclear power plant in Fukui Prefecture in April, an expert panel of the Nuclear and Industrial Safety Agency said the possible movement of the Urasoko Fault, an active fault running within the plant site, would likely cause a nearby fault directly under a reactor to move as well.
During a meeting of the panel July 17, one expert said a fault running right under the Shika plant is “a typical active fault,” expressing his surprise at the fact that the plant’s location passed the initial screening process.
These findings have highlighted afresh the disturbing ineffectiveness of the nuclear safety regulations.
But part of the blame also rests with electric utilities.
Even when experts pointed out the possibility of the existence of active faults, utilities kept denying that the faults posed safety threats without publishing sufficient materials and information to support their arguments.
The Diet’s investigative committee that has looked into the Fukushima nuclear disaster criticized both the government and electric utilities for having been reluctant to reform the nuclear safety regulations in response to new knowledge about tsunami. The panel said both the government and utilities feared new regulations could raise safety questions.
We are tempted to suspect that the government and utilities were also concerned that making active responses to the danger of active faults would jeopardize the operations of the nuclear power plants.
Japan is a highly quake-prone country. There must never be unfounded optimism about the safety of nuclear facilities, such as assuming that nothing serious will happen.
Investigations to determine whether the suspected active faults are actually dangerous ones are expected to take several months.
Meanwhile, the government plans to make the decision at the end of August on the future share of nuclear power in Japan’s overall energy supply.
But a decision on how much power should come from atomic energy in the future would be meaningless if it is made before the results of exhaustive investigations into possible active faults become clear.
The government should first make rigorous examinations to find out whether these faults are active or not and decommission all dangerous reactors immediately.
Even if such reactors are decommissioned, there are concerns that major earthquakes could destroy pools used to cool spent nuclear fuel.
It is vital to take necessary safety measures, such as transferring spent nuclear fuel from the pools into dry containers.
Investigations into the faults lying beneath the Oi nuclear power plant have yet to begin. But the government has already decided to restart the Nos. 3 and 4 reactors at the plant. And the No. 3 reactor is already running at full capacity.
Prime Minister Yoshihiko Noda has stressed the safety of these reactors.
But is it really possible to ensure the safety of operating these reactors while the possibility of active faults lying beneath them cannot be ruled out?
The government owes the public a clear and convincing answer to this question.
-- The Asahi Shimbun, July 19
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