Work to demolish the 110-metre tall chimney of the first Windscale plutonium-producing pile - which suffered a fire in its graphite core in 1957 - has begun at the UK's Sellafield site.
|The Windscale chimney (Image: Sellafield Ltd)
The chimney is the first of two to be built at Sellafield to service reactors which were used solely for making weapons-grade plutonium for Britain's nuclear weapons program.
The first reactor pile was damaged beyond repair by a fire that officially began on 10 October 1957. After many hours it was finally extinguished. Most of the radionuclides released were caught by the filters in the chimney, but some escaped and travelled in a plume across Britain. The accident was at the time the world's worst. Following the fire, the contaminated filters were removed from chimney, which was then sealed at the top.
The access area to where the filters had been located in Pile 1's chimney has now been opened to enable dismantling work to begin. It marks the first time that the chimney has been unsealed in over 17 years.
Work is currently underway to demolish the chimney's filter-holding structure. There is some 500 tonnes of structural materials including steel work, bricks and masonry in the filter section of the chimney alone. Some 66 tonnes of brickwork has already been removed from the external walls of the section. Over 5000 tonnes of materials in total will need to be removed during the full demolition of the chimney.
Unit 2, which was closed after the accident, was defuelled. However, its core - a 'pile' of graphite bricks - remains, as does unit 1's.
The height of the second chimney was reduced to the level of the adjacent reactor building in 2001.
"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," said Sellafield Ltd's head of decommissioning Steve Slater. He added, "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."
Pile chimney demolition manager Chris Wilson noted, "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."
Researched and written
by World Nuclear News