Sludge removal step in Sellafield clean-up

Sellafield 200A major step forward in the clean-up of Europe’s most complex nuclear site has been achieved by Sellafield Ltd.

The very first radioactive sludge has been removed from one of the most hazardous nuclear plants in Europe, a huge step forward in the UK’s nuclear decommissioning programme.

The First Generation Magnox Storage Pond (FGMSP) — which dates back to the 1950s and was constructed to store, cool and prepare used Magnox nuclear fuel for recycling into new fuel — urgently needs to be emptied of 1500 cubic metres of radioactive sludge lying at the bottom of the pond which is equivalent to more than half an Olympic sized swimming pool.

“We’re making history at Sellafield by transferring the first sludge using a tried and tested pump to a new £240 million state-of-the-art sludge storage plant containing three enormous stainless steel buffer storage vessels, each of which is the same volume as seven double decker buses,” Head of the FGMSP Martin Leafe said.

The vessels were brought to the Sellafield site in separate sections and then welded together before being carefully slid into the reinforced concrete building. The welding of each vessel involved over 2000 metres of weld run, which was done 99% right first time. All welds were then radiographed to ensure the required integrity and that there will be no leaks.

“Working with both Westinghouse and Energy Solutions, the technology already in use at European reactor stations has been adapted for our needs at Sellafield and rigorously tested in a full scale test facility at Forth Engineering here in West Cumbria,” Leafe added.

The sludge is a similar consistency to sand and has to be carefully removed, whilst leaving the water in place to provide a radioactive shield for the stored nuclear fuel. Its retrieval from the pond will enable the remaining radioactive inventory to be progressively removed to reduce the inherent hazard posed by the facility. The pond holds some 14,000m3 of contaminated water, in which is stored Magnox spent nuclear fuel, miscellaneous nuclear wastes and skips all of which is draped in blanket of radioactive sludge.

The pond has thick reinforced concrete walls however it was built with no roof and is open to the elements, so sludge has been accumulating at the bottom of the pond just like in any other garden pond. The difference is that this sludge is radioactive made up of nuclear fuel corrosion products, algae and windblown material, so it requires careful handling.

“The pond is six metres deep and we’ve spent years devising an engineering solution to literally suck up the radioactive sludge from the bottom of the pond, which in places is over one metre deep. What makes the job more difficult is that the pond is very congested and full of large metal boxes containing nuclear fuel, so we need to work around these and ensure these remain fully submerged at all times. Just to make matters more difficult we have to drive the platform remotely from a control cabin to minimize the radiation dose to the workforce,” Leafe added.

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