(552.5297) WISE Amsterdam - The accident occurred when a basket ("carousel") containing spent fuel rods broke free of the remotely controlled lifting mechanism. The basket fell onto the closed door of the shaft leading to the spent fuel storage pond.
The operatives responded by spraying carbon dioxide gas over the fallen basket to prevent the fuel overheating or catching fire (the Magnox fuel used at Chapelcross contains uranium in metallic form which can catch fire if exposed to air).
At first BNFL suppressed news of the accident. After a report in The Sunday Herald, BNFL admitted the accident but said that the basket fell 2 feet (0.6 meters). Later BNFL admitted that 12 of the 24 fuel rods probably fell 83 feet (25 meters)! This led to Energy Minister Brian Wilson commenting: "I will expect an explanation of why the initial information about what happened at Chapelcross seems to have fallen some way short of the reality".
Where exactly the rods have fallen is not entirely clear. Using remote cameras, BNFL found that 12 of the fuel rods were still in the discharge basket. However, as at 16 July - 11 days after the incident - they still could not find the other 12 rods, but assumed they had fallen to the bottom of the shaft. BNFL announced on 14 July that the other three Chapelcross reactors would be shut down so that "all the station's resources can be concentrated on the fuel recovery program."
Each spent fuel rod is approximately 1 meter long, 5cm in diameter and weighs between 10-12 kg. During IAEA tests in which a Magnox transport flask was "drop-tested" from a height of 9 meters, fuel rods have sometimes broken open inside the flask. If any of the rods which have fallen 25 meters have broken, there remains a risk that they could catch fire, resulting in a major release of radioactivity. BNFL say that tests have so far shown no raised levels of radioactivity.
The accident is not the first time there have been problems with the de-fueling system. Just two months ago, a grab-release mechanism failed during de-fueling operations at Chapelcross.
Chapelcross was opened in 1959 and consists of four 50MW Magnox reactors. The reactors are dual-use: besides electricity production, the reactors have produced plutonium for Britain's nuclear weapons program. The site is also home to a military plant that produces tritium for Trident warheads.
In 1967 there was a partial meltdown in reactor no.2 at Chapelcross, and the reactor was closed for two years. The extent of the 1967 accident was kept secret for many years. The meltdown apparently began when a fuel rod broke and caught fire. The press were told at the time that no radioactivity was released, which later turned out to be untrue.
The Calder Hall reactors at Sellafield - the world's first power reactors, opened in 1956 - are of a similar design to Chapelcross, and de-fueling operations there have also been suspended as a precaution, according to BNFL.
Sources:
- CORE Briefing, 9 and 16 July 2001
- The Sunday Herald, 8 July 2001
- BBC News, 13 and 14 July 2001
- N-Base Briefing, 14 July 2001
- The Guardian, 13 October 1986 and 9 February 1988
- Platts Nuclear News Flashes, 13 July 2001
Contact: Cumbrians Opposed to a Radioactive Environment (CORE), 98 Church Street, Barrow,
Cumbria LA14 2HJ, UK
Tel: +44 1229 833851; Fax: +44 1229 812239
E-mail info@core.furness.co.uk
Web: www.corecumbria.co.uk
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