Sharper sense of safety urged at nuclear facilities

原子力産業の最重要課題

    The head of the commission acknowledges in the foreword that last August's tragedy in Mihama, Fukui Prefecture — Japan's deadliest nuclear accident — 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 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 malfunctions, including minor ones, occurred in 2004. The number might have been reduced if safety laws and regulations had been followed more strictly. But 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 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 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 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 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 is to assure the safety of nuclear plants and facilities beyond any reasonable doubt.

The Japan Times Weekly
May 21, 2005
(C) All rights reserved

      松浦祥次郎委員長は白書のはしがきで、昨年8月に死者5人、負傷者6人を出した関西電力美浜原子力発電所の蒸気噴出事故は、予防措置が十分であれば防げたはずと振り返った。死傷者は、破損した配管から漏れた高熱蒸気に襲われた。99年には茨城県東海村の民間ウラン加工施設で2人が被爆、死亡している。

      各種の安全技術は、人為的ミスは避けられないという前提で開発されてきたが、それで事故をすべて防止できるわけではない。現在の原子力産業で絶対安全はあり得ない。

      白書によれば、04年に24件の事故、故障が原子力施設で起きた。安全に関する法律、規則が順守されていれば、件数は減った可能性があるが、規則は安全を保証しない。

      したがって、現場の管理者、労働者が安全意識を高めることが絶対に必要になる。

      松浦委員長は、美浜原発事故の根源に怠慢があることを認めている。配管の腐食を防ぐことは技術的に可能だったばかりでなく、関係者は腐食の可能性を認識していながら隠していた。

      美浜事故は原発の老朽化の問題も浮き彫りにした。操業開始後27年の美浜原発は業界基準では老朽化していなくても、原子炉の配管は腐食が進み、部分的に紙1枚の薄さになっていた。

      全国で運転中の53基のうち、いくつもの原子炉が運転開始後30年以上を経過している。現在の基準では、原子炉の寿命を40年以上としており、今後10年間で多くの原子炉が運転開始後30年を迎える。

      原子炉の老朽化は緩慢に進行する。老朽化の兆候を見逃すと、美浜事故のような大事故が起きる可能性がある。海外の老朽化した原子炉の例が事故防止に役に立つ可能性がある。

      白書はまた、原子炉の廃棄に関する安全について触れている。現在の安全規則は、原発の建設、運転に関するもので、その廃棄についてはカバーしていない。原子炉等規制法の改正法案が国会に上程されているのは当然である。

      続発する事故、故障は原子力産業、政府への警告である。原発、その他の原子力施設で安全を確保することを最優先課題とすべきである。