Sellafield is Europe's largest nuclear site and although operations including spent fuel management and nuclear waste storage continue on-site, power generation ceased in 2003. As part of the decommissioning process, the site's tallest chimney will now be demolished.

"This is part of a whole program of decommissioning work that is being carried out at Sellafield to clean-up historic nuclear facilities, many of which were built in the 1940s and 1950s in support of the defense industry," explains Ali McKibbin of Sellafield Ltd, the company responsible for delivering the decommissioning, to Gizmag.

The chimney is 61 m (200 ft) tall and sits on top of an 11-story reprocessing plant. The entire structure reaches 122 m (400 ft) above the ground. Its location, atop the reprocessing plant and surround by other nuclear facilities which are still in operation, means that the demolition of the chimney be undertaken without explosives.

"The job of bringing down the stack is going to be a delicate operation to ensure 100 percent safety of all personnel and surrounding nuclear plants," explains project manager Matthew Hodgson. "Because we can’t use explosives, we will use an ingenious self-climbing platform which will [allow us to] bring the chimney down bit by bit in a controlled manner."

The technique was used recently during the dismantling and rebuilding of the chimneys at Battersea Power Station. The platform will be built around the chimney and electric screw jacks will be used to raise and lower it.

The middle level of the platform is used as a workspace for the dismantling of the concrete windshield exterior of the chimney using a diamond wire cutting system. The upper level of the platform is used as a workspace for dismantling the internal stainless steel flue liner. Flooring is installed inside the flue to provide access, before plasma arc cutting or cold cutting techniques are used to reduce its size.

By using the platform in this way, work can be carried out removing the internal flue where the external windshield has already been removed. At the same time, work can continue on removing a lower part of the windshield in preparation for work on the flue when the platform is lowered.

In total, the project will see the dismantling of 600 tonnes of concrete and rebar and over 25 tonnes of stainless steel. Sellafield's Windscale chimneys are also in the process of being dismantled.