The government has worked out a revision of the law on the control of nuclear reactors. Under the revision, the operational life span of a reactor will be legally limited to 40 years — in principle. But the revision contains an exception clause, modeled after one in use in the United States, for extending this limit. Also under the revision, a nuclear power station operator will be legally obligated to prepare for severe accidents by adopting such measures as establishing as multiple redundancy of power sources for reactor operations and taking steps to prevent the flooding of reactors. Thus far, reactor operators have employed such measures only on a voluntary basis. Technical standards will be drawn up using the latest knowledge, and nuclear power stations already in operation must pass them.

If the 40-year life span limit is strictly enforced, it will reduce the share of nuclear power in Japan’s total power generation. The exception clause could permit the extension of an operational life span for up to 20 years if reactor operators make such a request and a government inspection determines that the reactors are in safe working order and the operator can keep them this way. The government carried out an inspection on the Fukushima No. 1 reactor in 2010 and extended its license to operate by 10 years just weeks before the March 11 disaster struck and severely damaged the 40-year-old reactor.

The danger is that the government and power industry abuse the exception clause thereby going against public sentiment in favor of phasing out nuclear power.

At present, there are 54 commercial reactors in Japan. Three of them — the No. 1 reactor of the Fukushima No. 1 nuclear station, the No. 1 reactor in Tsuruga, Fukui Prefecture, and the No. 1 reactor in Mihama, Fukui Prefecture — are more than 40 years old.

In July, the No. 2 reactor in Mihama will be 40 years old. Since construction of new nuclear power plants is unlikely, the number of reactors will decline to 35 in 10 years and to 16 years in 20 years if the 40-year rule is strictly enforced.

But the 40-year rule does not necessarily mean that reactors in operation for less than 40 years are safe. The Nos. 2 to 4 reactors at the Fukushima No. 1 nuclear power plant, which sustained severe damage on March 11, were all more than 30 years old. Fears have been raised that the condition of the 36-year-old No. 1 reactor in Genkai, Saga Prefecture, has deteriorated due to bombardment by neutrons. The government must carry out especially stringent inspections of all reactors in operation for more than 30 years.

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