The diffuser gave the 125-metre chimney its distinctive top-heavy appearance. It has loomed over the west Cumbrian landscape for nearly 70 years. But after three years of precision dismantling, it has now been cleared.
The diffuser had to be cut up in-situ, more than 100 metres above ground. Sections were then transported separately down to the ground. It required 200 moves to clear the entire block. Much of the work took place during the Covid-19 pandemic.
Work is now taking place to remove a metal frame platform and reduce the access shaft. Following this, work will start on demolishing the chimney barrel.
This surgical demolition also removed the seismic risk associated with the chimney.
Demolition work started in December 2018. The first block was removed from the diffuser in January 2019.
A total of 226 blocks have been removed from the top of the chimney stack, reducing the height of the stack by 15.42 metres. Each block weighed between two and nine tonnes; the total weight of all 226 blocks was 1,232 tonnes
The sections of the diffuser structure have been cut by machine using diamond wire saws. These cut blocks were removed from the top of the stack and lowered into the controlled area canopies ground using a tower crane.
The blocks were then remediated and transferred to the bagging station on the Sellafield site where a Goliath crane was used to manoeuvre the blocks ready for transport to interim storage prior to disposal.
This was either to the Calder Landfill Extension Segregated Area on the Sellafield site, or Low Level Waste Repository, dependent on contamination levels and conditions for acceptance at each location.
Sellafield Ltd project manager Geoff Carver said: “Removing the seismic risk is a huge achievement. This is a clear demonstration of progress towards our purpose of delivering a clean and safe environment for future generations. Many people have contributed to this success. Sellafield Ltd employees have worked closely with their colleagues from our partners ADAPT, Doosan, Mammoet, KDC, Kaefer, the Design Services Alliance, and Nuvia.”
David Peattie, chief executive of the Nuclear Decommissioning Authority(NDA), said: “This is an excellent example of the pioneering work taking place on our sites to deal with the legacy of the earliest days of the nuclear industry. In reaching this significant milestone of removing the Windscale Pile Chimney diffuser, we take another step forward in our clean-up mission.”
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