Standing 110 metres high and dominating the West Cumbrian skyline since its construction in the 1940s, Windscale pile chimney number one was one of the first parts of the Sellafield site to be constructed.
It was the first of two pile chimneys built to service reactors used to make weapons grade plutonium during the cold war, and then in 1957 was the scene of what remains the only significant nuclear accident to ever occur in the UK.
Now, over 50 years since operations ceased following the fire, work on cleaning up and decommissioning the pile number one is moving forward.
The first, and most challenging, step is to remove the filter gallery from the top of the chimney.
Nobel prize-winning physicist and nuclear pioneer John Cockcroft insisted that the filter galleries were added to the chimney’s after construction work had started, because he was concerned that there was no way to contain radiation in the result of an accident.
Because the work had already started it was too late to put the filters near the reactors at the bottom of the piles, meaning they were added to the top. Nuclear workers at the time felt Cockcroft’s approach, which was incredibly expensive and caused a delay, was over the top, earning the filter galleries the nickname “Cockcroft’s Follies.” However, during the fire in 1957 the filter gallery on pile number one stopped what remainsBritain’s worst nuclear incident from becoming a catastrophe. It absorbed the vast majority of the contamination, so while some radiation was spread across the region, most was contained within the filter gallery.
Following the fire the chimneys were sealed at the top and the contaminated filters removed, so air inlet ducts could be isolated. Radiation levels had to reduce significantly before decommissioning work could start. The first chimney was reduced to the level of the adjacent reactor building in 2001, but the second chimney posed more of a challenge due to radioactive contamination from the fire.
However, with much of the radiation having now decayed, chimney number one has been opened up for the first time in over 17 years to enable work on dismantling it to begin. The filter dismantling access gantry, which is made up of 52 tonnes of structural steel work, was pulled open by Sellafield Ltd engineers.
Steve Slater, Head of Decommissioning said: “The decommissioning challenges posed by the pile chimney are unique – no other structure in the world provides the same complexity in terms of both radiological and conventional decommissioning constraints. Bringing the chimney down will be a real visual demonstration of our commitment to cleaning up Sellafield.
“Over 50 year after the Windscale Pile reactors ceased operation, the familiar landmarks of the West Cumbrian skyline are disappearing. The chimneys were a real technical achievement in terms of construction, which minimized the effect of the fire in 1957 and are testament to the nuclear pioneers who built them.
“Today, we’re using the considerable nuclear expertise built up at Sellafield to safely bring the final chimney down. The plan is to remove the filter gallery by the end of next year and then the chimney diffuser by 2018. 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. Already 66 tonnes of brickwork has been removed from the filter gallery external walls, and taken down from the top of the chimney in a small goods hoist.
Chris Wilson, Pile Chimney Demolition Manager: “It’s taken many years of real effort and energy 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.
“There have been many significant challenges to overcome in preparing for the physical demolition of the chimney, not least coming up with an agreed plan with the neighbouring nuclear plants on the congested Sellafield site. We are also working hard to put in place a sizable workforce with the right skills to carry out the job.”
The chimney is 110 metres tall and there is approximately 500 tonnes of structural materials including steel work, bricks and masonry in the filter gallery section of the chimney, with over 5000 tonnes of materials in total to be removed during full demolition of the chimney to ground level.