10 October 2007

The Windscale Fire

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Today is the 50th anniversary of Britain’s worst nuclear accidents. On 10 October 1957 a fire ripped through the radioactive materials in the core of Windscale , Britain's first nuclear reactor site. .Ever increasing pressure to deliver materials for Britain’s nuclear programmes led to compromised safety. When the accident happened it was the staff who were scapegoated.

Two reactors were built at Windscale Windscale in Cumbria in the late 1940s. Their initial purpose was to produce plutonium for British atomic weapon programme. The reactors were operational in 1950 and the first British nuclear weapon was detonated in 1952. Along with Calder Hall, the world’s first nuclear power station which opened in 1956, the reactors were subsequently used to produce tritium for the British H-Bomb programme. The Windscale reactors themselves were graphite moderated and air cooled.

Hungarian physicist Eugene Wigner discovered that graphite will suffer dislocations in its crystalline structure when bombarded by neutrons (as happens during its operation) and that this will cause a build up of potential energy. If allowed to accumulate the energy could escape spontaneously in a powerful and very dangerous rush of heat. The only viable way to deal with “Wigner energy” was to anneal the graphite – heat it to 250 degrees Celsius thus expanding the graphite and allowing a gradual release of energy.

It was during a routine exercise to release Wigner energy that the fire took place. Inadequate monitoring equipment meant that the control room staff mistakenly thought the reactor was cooling during the annealing process and so needed an extra boost of heating. In fact temperatures were rising. When there the reactor's chain reaction was restarted to increase core temperature a fuel canister burst and ignited. Further canisters burst and the ignition of further material sent temperatures soaring, eventually to 1,300 degrees Celsius. In an effort to help cool the pile, extra air was pumped through the core. This simply fanned the flames and flushed radioactive material from the reactor, more that could be handled by its air filtration system. As a result a large amount of radioactive material was released into the air. An attempt to damp the fire with CO2 was equally unsuccessful. Ultimately the operators decided to try cooling the core with water. This was a very risky procedure as it could have led to an explosion destroying the reactor. The consequences would of course have been terrible.

Tom Tuohy, the deputy general manager at the site, led the team faced with dealing with the fire: "Mankind had never faced a situation like this; there's no-one to give you any advice," he said. In addition pumping water into the core, the air cooling system was turned off. The combination was successful and the fire was put out

The fire itself released an estimated a substantial; amount of radioactive material into the environment (an estimated 700 terrabecquerels or 20,000 curies). No one was evacuated from the surrounding area, but for a month after the incident milk from about 200 Square Miles of nearby countryside was destroyed. There were no fatalities during the accident itself but it is estimated that it was responsible for over 200 additional cancer cases.

An enquiry was conducted by William Penney, the man responsible for developing Britain’s Atomic and Hydrogen bombs. He learned that scientists had been warning about the dangers of an accident for some time. There were serious concerns that safety margins had been increasingly eroded. However the politicians and the military ignored the warnings; instead they increased demands on Windscale to produce material for an H-bomb.

A succession of Prime Ministers from Clement Attlee onwards had been determined to persuade the Americans to share the secret of their nuclear weapons with Britain. Harold Macmillan believed that, if Britain could develop an H-bomb on the scale of the Americans', they would treat it as a nuclear equal and form an alliance. In fact at the time of the accident Macmillan was arranging a summit in Washington where they would announce the Declaration of Common Purpose in which the US would share nuclear secrets with the UK, Macmillan realised that if the American Congress knew that the fire had been the result of reckless decisions taken to try to produce the-H bomb, they might veto Macmillan and Eisenhower's plans. Macmillan therefore issued a report that said the accident had been caused by "an error of judgement" by the Windscale workers and for 50 years, the official record on the accident has been that the very men who had averted a potentially devastating accident were to blame for causing it.

A television programme about the incident was aired on BBC2 on Monday featuring many of the people who had worked at Windscale at the time, including Tom Tuohy. Needless to say they remain bitter at their treatment. At the very end of the programme Mr Tuohy was asked what he thought of the officials who the Americans think that his men were responsible for the conflagration, he said “I thought that they were a shower of bastards.”

The Windscale reactor was unsalvageable; It was sealed with over 9,000 fuel elements and isotope canisters still inside. The damaged reactor core is still slightly warm as a result of continuing nuclear reactions - The final removal of fuel from the reactor is scheduled to start next year (2008). The second reactor was also shut doen over safety fears and not further air-cooled reactors were built in the UK.


Crushed said...

I didn't know it was bring used for H-bomb purposes.

I still think Nuclear power is on the whole the best option, however.

jams o donnell said...

I hope we don't se anything of this sort again. Personally I am very uneasy about nuclear power but it will be providing a significant part of our energy output for a long time yet.

Archie said...

As someone born in the shadow of Sellafield I have been following the coverage of the anniversary with interest.

Nuclear power is much safer now and I agree that it remains the best option to meet medium term energy needs.

jams o donnell said...

My biggest concern has always ben the storage of amterial that is dangerous for millennia. In the medium term I agree it is a better choice that more fossil fuel burning. Hopefully alternatives can be made to provide a substantial part of our needs in the future

Steve Bates said...

An exaltation of larks... a murder of crows... a shower of bastards...

When they convince me they've solved not only the reactor safety problem but also the waste disposal problem... and I don't mean entombing it in caves or dumping it in open trenches in west Texas... I may consider nuclear power. Until then, I believe it's even less safe than burning things. And like burning things, nuclear power contributes to climate change. As I recently commented elsewhere, I prefer my nuclear power to be generated a long distance away from me, say, the distance from the Earth to the Sun.

(I am probably posting this using nuclear power; there's a plant in South Texas, so one never knows.)

jams o donnell said...

My biggest concern Steve is wasste disposal. Keeping radiocaive material safe that will be dangerous for millennia? Something tells me that there will be some serious leaks before that problem is licked...