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The latest annual report from Japan’s Nuclear Safety Commission is a troubling reminder that accident prevention remains a key priority for the nation’s nuclear power industry. The head of the commission acknowledges in the foreword that last August’s tragedy in Mihama, Fukui Prefecture — Japan’s deadliest nuclear accident ever — could have been prevented if sufficient precautions had been taken.

The accident, which killed five workers and injured six others, involved the rupture of a water pipe in one of the reactors of Kansai Electric Power Co. The affected workers were heavily exposed to superheated steam bursting from the broken section of pipe. In September 1999, two workers died from radiation exposure at a uranium-purification facility in Tokaimura, Ibaraki Prefecture.

The basic assumption is that people are liable to make mistakes. To make up for human shortcomings, a wide array of safety technologies have been developed. But believing that technologies can eliminate all accidents once and for all is wishful thinking. In the nuclear industry, at least in its present stages of development, there is no such thing as absolute safety.

According to the white paper, as many as 24 accidents and disorders, including minor ones, occurred in 2004. The number might have been reduced if safety laws and regulations had been followed more strictly. But, again, these rules cannot provide absolute guarantees of safety. They do not always apply to specific risks and dangers that may arise in the course of day-to-day operations.

That is why it is absolutely necessary to raise the level of safety awareness among those involved, particularly frontline managers and workers. Experience shows clearly, and tragically, that lapses in mental alertness and attitude toward safety can lead to major accidents.

In fact, as the commission’s chairman admits, negligence was the underlying factor in the Mihama accident. The pipe corrosion that directly caused its rupture was preventable not only because it was technically possible to stop the thinning of the pipe wall, but also because some of the people involved knew where it would occur yet kept that knowledge to themselves.

The Mihama tragedy has focused attention on another critical problem: the aging of nuclear plants. The Mihama reactor involved had gone into operation 27 years earlier. That’s not “old” by industry standards, but the steady corrosion of the pipe — wall thickness in the affected area was said to be as thin as paper — demonstrated that the pipe was aging steadily.

At present, 53 reactors are in operation across the country. A number of them are reportedly more than 30 years old, the oldest being 35. Current operation plans put the service life at 40 years or more. This means that many reactors will top 30 years old in the next decade, which is considered “advanced in age.”

As the report points out, the aging problem is compounded by the fact that it develops very slowly. This makes it difficult, if not impossible, to detect early signs of aging. If these signs are overlooked, they may lead eventually to disaster, as happened in the Mihama No. 3 reactor.

The aging process involves a complex combination of factors, including heat, water flows, vibrations and radiation. Because of this, experts say, the process is likely to take various — and possibly unpredictable — forms, depending on how these factors interact. In this respect, experience at older nuclear plants overseas should provide useful lessons.

Notably, the white paper takes up a question that has not received much attention in the past: how to ensure safety when obsolescent nuclear facilities are dismantled. A case in point is the Japan Atomic Energy Research Institute’s experimental power reactor, which, after 13 years of operation, was scrapped over a period of 10 years beginning in 1986. Its radioactive waste was also disposed of.

The fact is that current safety regulations focus on the construction and operation of nuclear facilities, but not on their dismantlement. Rightly, a bill to update the law governing nuclear reactors is now being discussed in the Diet. It responds to a commission report calling for a review of safety rules for the disassembly of nuclear facilities.

As nuclear safety goes, experience still seems lacking in many respects, despite decades of operation. Indeed, the poor safety record is a constant wake-up call to the nuclear industry as well as the government. Their priority task, now and in the future, is to assure the safety of nuclear plants and facilities beyond any reasonable doubt.

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