Windscale chimney finally opened for demolition work11 September 2013

Work on decommissioning the last remaining Windscale chimney – a a major part of the Sellafield skyline since the 1940s – is now underway.

The filter dismantling access gantry, made up of 52 tonnes of structural steel work, has been pulled apart to open the chimney for the first time in more than 17 years, in preparation for dismantling.

"The decommissioning challenges posed by the pile chimney are unique," says Jeremy Hunt, head of decommissioning projects. "No other structure in the world provides the same complexity, in terms of both radiological and conventional decommissioning constraints."

The original two pile chimneys were ventilation shafts, rather than chimneys, discharging cooling air from the Windscale Pile Reactors – conceived in the aftermath of the war, as part of the drive to develop a nuclear deterrent.

The remaining pile chimney worked as a ventilation shaft for Windscale Pile One, which caught fire in 1957. The high performance filters fitted at the top of the chimney prevented much of the contamination escaping to the local area, but the decision was taken then to shut down both Windscale Piles.

It was Nobel prize-winning physicist John Cockcroft who insisted that the Windscale Pile chimneys be fitted, at great expense, with high performance filters. But since the decision came after the stacks had been designed and partially built, they resulted in the iconic bulges at the top of the structures, known as the Cockcroft's Follies.

Ironically, it was these filters that prevented the Windscale Fire disaster from becoming a catastrophe.

"Today, we're using the considerable nuclear expertise built up at Sellafield to safely bring the final chimney down," comments Steve Slater, head of decommissioning.

"The plan is to remove the filter gallery by the end of next year and then the chimney diffuser by 2018 to meet the requirements of our customer the Nuclear Decommissioning Authority," he continues.

"A tower crane will be built alongside the chimney and the chimney barrel itself will then be dismantled and lowered down in sections."

Work is now underway for the demolition of the filter gallery structure. Some 66 tonnes of brickwork have been removed from the filter gallery external walls and all of this has been transferred from the top of the chimney in a small goods hoist which runs up and down the outside of the chimney.

Chris Wilson, pile chimney demolition manager says it's taken many years to develop a robust, safe and effective plan for the chimney demolition.

"For the first time in decades, we are able to confidently progress the safe dismantling and demolition of this historic and iconic UK nuclear legacy," he declares.

Brian Tinham

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