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Highly challenging

A giant crane has helped shave 18 months off a key decommissioning project at Sellafield. NCE reports.

sellafield2

Main event: Heavy lifting specialist Mammoet supplied the 1,200t crane to position the new pipe bridge

One of the most technically challenging crane lifts ever performed on the Sellafield nuclear site was completed successfully at the end of last year as part of a project to transfer radioactive sludge into storage. With space extremely tight, and a heavy and awkward load, just getting permission to carry out the work was a challenge in itself.

The job involved lifting a 50t pipe bridge into place to link a 60 year old legacy pond with a new sludge storage facility. The 30m long pipe bridge will be used to transfer radioactive sludge from the first generation Magnox storage pond (FGMSP) to a new sludge packaging plant (SPP1) for interim storage.

“It was an immense challenge for the team to plan and get this job approved,” says Sellafield project manager Steve Harnwell. “Failure wasn’t an option.

“The job involved convincing ourselves, the safety experts and our safety regulators that we could safely build one of the world’s largest mobile cranes in the heart of the Sellafield site,” he adds. “Just finding enough space between the buildings was a challenge, never mind lifting the pipe bridge over the top of neighbouring nuclear facilities.”

Harnwell describes the lift as “a mammoth task, carried out with an enormous crane, which had to be executed with surgical precision”. Before the actual lift, the team had a “dummy run” off site to check that the whole lifting operation could physically be done.

The FGMSP is one of Sellafield’s priority decommissioning projects, as the legacy sludge has to be retrieved from the pond floor so the pond can be emptied of nuclear fuel and the facility decommissioned.

“The job involved convincing ourselves, the safety experts and our safety regulators that we could safely build one of the world’s largest mobile cranes”

Steve Harnwell, Sellafield

Installing the pipe bridge will allow retrieval of the sludge to begin in 2014, and provide a valuable back-up emergency route for the FGMSP, before it is emptied.

In advance of the lift, preparations for the crane required 40m3 of concrete foundations to be poured to provide a stable base for the lifting operations. The 1,200t crane - supplied by heavy lifting specialist Mammoet - travelled to site on a number of wagons, and a second 100t crane was used to prepare the site and erect the larger crane.

“The crane lift shows what good work can be achieved by challenging norms and expectations,” says Nuclear Decommissioning Agency head of programme, Sellafield, Mark Steele. Assembling the pipe bridge off site and putting arrangements for the crane lift in place have saved significant work on site and allowed the task to be completed some 18 months earlier than scheduled.

“We appreciate the efforts by the project team and all involved on the site and in the supply chain. It’s good to see these initiatives being grasped by the programme and the more support we can all give to these endeavours the better,” says Steele.

The FGMSP was constructed in the 1950s to store, cool and prepare Magnox fuel for reprocessing. During its 26 year operating lifetime it processed almost 2.5M fuel rods containing 27,000t of fuel.

The pond now holds 14,000m3 of contaminated water that contains spent nuclear fuel, radioactive sludge, miscellaneous nuclear waste and skips.

The new sludge packaging plant (SPP1) is being built to receive over 1,200m3 of legacy sludge from the FGMSP. It comprises three stainless steel buffer storage vessels to contain the sludge and allow it to decant and settle. This will then enable the sludge to be properly processed and disposed of.

Each storage vessel measures 33m long, 7m high and 3m wide, and weighs 240t.

Site clearance for SPP1 began in November 2005, and installation of the three stainless steel buffer storage vessels was completed in 2012.

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