Wednesday, 6 April 2011

Nuclear accidents

It's interesting how after every nuclear 'accident' or disaster we hear the same mantra, 'lessons learnt... can't happen again. Only it does.

Britain is certainly not squeaky clean. There was the Windscale fire of 10 October 1957, ranked in severity at level 5 on the 7 point International Nuclear Event Scale. The graphite core of a nuclear reactor caught fire releasing substantial amounts of radioactive contaminants.

Then there was the incident at the Wylfa Magnox power station on Anglesey on 31st July 1993. A 3ft long, 130lb steel grab on the end of crane used to lift nuclear fuel rods broke off and fell 40ft into a reactor. It lodged in one of the 6,150 fuel channels in the reactor, blocking a small part of the flow of carbon dioxide coolant gas through the structure. After control room staff detected the breakage they allowed the reactor to keep operating for nine hours before shutting it down.

In 2005 a leak of highly radioactive nuclear fuel dissolved in concentrated nitric acid, enough to half fill an Olympic-size swimming pool, forced the closure of Sellafield's Thorp reprocessing plant. The highly dangerous mixture, containing about 20 tonnes of uranium and plutonium fuel, leaked through a fractured pipe into a huge stainless steel chamber which was radioactive that it was impossible for workers to enter.

Finally there's Japan and the Tokai-mura accident in 1999 a direct product of cost-cutting and appalling safety standards.

The JCO Corporation, which operated the Tokai-mura plant, ran an experimental reactor known as Joyo. The process involved mixing a uranium oxide with nitric acid in a dissolving tank to produce uranyl nitrate. JCO had altered the safety manual to permit workers to combine uranium oxide and nitric acid in steel buckets rather than the dissolving tank. The solution was manually poured into the buffer tank.

To save time the untrained and unsupervised workers mixed seven buckets, or some 16 kilograms, and poured them directly into the precipitation tank instead of the specially shaped buffer tank. As the seventh bucket was poured in the mixture reached critical mass initiating a sustained chain reaction.

The nuclear reaction lasted up to 20 hours exposing the plant and 500 metres beyond to levels of radiation many times above the official safe dose.

No government regulator had inspected the operation in 10 years. As a result the Labor Ministry conducted inspections of 17 facilities. Health and safety violations were found at 15. Inspections of nine nuclear fuel processing plants and laboratories found 25 violations ranging from inadequate training of staff, failure to provide workers with regular medical checkups and failure to report radiation exposures.

Lessons learnt in time for Fukushima?

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