Remotely operated mini submarines have been used at the Sellafield nuclear site to demonstrate just how radioactive sludge could be removed from the bottom of a historic fuel storage pond.

DECOMMISSIONING

Remotely operated mini submarines have been used at the Sellafield nuclear site to demonstrate just how radioactive sludge could be removed from the bottom of a historic fuel storage pond.

One of the biggest decommissioning challenges at Sellafield is the First Generation Magnox Storage Pond (FGMSP) which handled 27,000 tonnes of nuclear fuel over its lifetime. It is estimated that there is up to 1500 cubic metres of radioactive sludge left in the 60-year-old pond – that’s equivalent to more than half an Olympic swimming pool.

The 1950s 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 garden pond. The sludge is made up of algae, corrosion products and wind-blown material but is radioactive and therefore needs careful handling.

Martin Leafe, Head of the facility added: “We’ve taken technology used in the hazardous deep sea conditions and applied it at Sellafield in our own hazardous nuclear fuel storage ponds. The mini submarines can explore, survey and carry out remote operations at the bottom of the pond, while the workers remain safe and dry outside the pond.

“We are building up our knowledge of the radioactive sludge characteristics to help develop equipment for bulk sludge retrievals, which will have to cope with sludge up to one-metre-deep in places. The greater our understanding of the sludge the more opportunities we will have to accelerate decommissioning of this priority project.

“Significant savings will be made using mini submarines rather than designing and building complex bespoke equipment which was our original plan. We now have the ability to clear space in this hugely congested storage pond to help with the recovery of nuclear fuel, contaminated waste and radioactive sludge as part of our work to empty this legacy facility.”

Sellafield Ltd has already built a Sludge Packaging Plant (SPP1) alongside the historic pond and inactive commissioning of the new plant is being carried out. Before it can start operating, some sludge has to be sucked up from the bottom of the seven-metre-deep pond to test it and that’s where the Remotely Operated Vehicles (ROVs) or mini submarines come in.

Dave Skilbeck, the facility manager said: “We are extending our Remotely Operated Vehicle (ROV) capability all the time to help empty this historic nuclear pond. Our experienced pilots can “fly” the machines within the pond to survey the fuel and sludge, take sludge samples for analysis, and pick up and consolidate nuclear fuel into fuel containers for export out of the pond.

“Our latest success has been attaching an eductor to the ROV which has proved that we can lift the sludge from the bottom of the pond. The eductor device is like a powerful jet pump that creates a negative pressure differential that draws the sludge up through a thick hose.

“We need about 50 cubic metres of sludge to commission and test the new Sludge Processing Plant later this year and we’ve now proved the technology to get the job done. We can safely get the radioactive sludge off the bottom of the pond whilst leaving behind the water which is a significant step forward.”

Radioactive sludge to a depth of 30 centimetres was successfully removed from a small area of the pond floor right down to the concrete base slab. This capability will be used to help pond floor clearance and will provide access to the containers of nuclear fuel that needs to be retrieved and moved to modern storage.

The radioactive sludge is thick and although the eductor had been previously trialed using simulant materials, there was no guarantee that it would be effective when introduced into the FGMSP. Video footage was taken by the ROV and it shows this grey sludge being pulled up through the hose and the yellow uranium is clearly visible.

Further trials are now being carried out to capture and temporarily store the sludge, before it is turned into a consistency suitable to start pumping it across to the new SSP1 at the end of 2014.

Notes for Editors

First Generation Magnox Pond

The FGMSP was constructed in the 1950s to store, cool and prepare Magnox fuel for reprocessing. During its 26 year operating lifetime it processed approximately 27,000 tonnes of fuel (almost 2.5 million fuel rods). Spent nuclear fuel from the UK’s nine Magnox stations, along with Magnox fuel from both Italy and Japan was held in the FGMSP.

The 1950s original building comprised an inlet building for incoming fuel, an open air storage pond, a building containing wet bays for fuel cladding removal and a sludge settling pond. The 1960s extension provided additional pond storage capacity and new large caves for improved fuel cladding removal.

Since 1992 the plant has been in the Post Operational Clean Out (POCO) phase of decommissioning. Considerable work has been carried out improving the condition of the building, installing new equipment and removing redundant facilities in order to allow the safe retrieval of the nuclear materials stored in the pond.

Sludge Packaging Plant

The new Sludge Packaging Plant (SPP1) has been built alongside the FGMSP to hydraulically receive and store the retrieved sludge. It includes three stainless steel buffer storage vessels to contain the sludge. In the future the tanks will be emptied and the sludge processed into a form suitable for final disposal.

Inactive commissioning of the SPP1 is already underway and as part of this the water testing of the buffer storage vessels has commenced. This will test the integrity of the vessel loading and the design stresses. It is anticipated that the plant will be available late 2014 to support the commencement of sludge retrievals.

Sellafield Ltd

Sellafield Ltd is the company responsible for safely delivering decommissioning of the UK’s nuclear legacy as well as fuel recycling and the management of low, high and intermediate level nuclear waste activities on behalf of the Nuclear Decommissioning Authority

NMP

Since 2008, Nuclear Management Partners (NMP) has owned and operated Sellafield Ltd. NMP combines the global nuclear experience of US company URS, British company AMEC, and French company AREVA to manage Sellafield Ltd, a unique site with the most diverse portfolio of any nuclear facility in the world. Together with Sellafield Ltd we are delivering the Nuclear Decommissioning Authority’s mission of accelerated clean-up at Sellafield.

More information can be requested from either info@rovtechsolutions.co.uk or by calling 01229 822121