'Metal Mickey' helps de-sludge Windscale pond

16 September 2008

De-sludging activities have begun in the Windscale Pile Fuel Storage Pond at the Sellafield site in the UK. Plant operators are being assisted in the project by Metal Mickey, a remotely operated vehicle.

Sellafield B29 (Sellafield Sites) 
The open-air B29 cooling pond reflects
an image of the remaining Windscale
stack (Image: Sellafield Sites)
The pond - built and commissioned between 1948 and 1952 - and the adjoining Decanning Building provided the storage and cooling facility for irradiated fuel and isotopes from the two Windscale pile reactors. The pond processed 2100 tonnes equivalent (te) of pile fuel and 300te of Magnox fuel. All operations in the pond ceased in the 1970s.

The sub-divided outdoor storage pond is some 100 metres long, 25 metres wide, 7 metres deep and contains over 14 million litres of water. It contains skips of irradiated fuel and waste, each skip containing up to six cubic metres of material. The building contains a series of sub-ponds, or 'bays', connected underwater to the main pond.

Sludge, in the form of corrosion products and wind blown material, which has accumulated in the pond since it was commissioned in 1952, is being mobilised by the use of water lances and flushed into the main pond. It is then being retrieved and moved into an enclosure in the pond.

The initial phase of the project is the retrieval of sludge from two of the original twelve bays within the pond, in which fuel was decanned and exported for processing. Metal Mickey will help workers reach some of the more inaccessible areas of the pond. The contents of the pond, some of which had been displaced over the years, were mapped by another submersible robot in a preliminary stage.

Later phases of the project will see sludge transferred from the enclosure to a new facility which is currently being constructed adjacent to the pond, for interim storage prior to final treatment.

Steve Topping, head of delivery, said: "We have started de-sludging one of the highest hazard facilities at Sellafield and we shouldn't underestimate the importance of this for the site and local community or the UK nuclear industry as a whole."

The Local Effluent Treatment Plant has also begun operating at Sellafield, which will treat the pond water.

Topping added, "Activity levels in the pond may be affected by the sludge retrieval operations. What the Local Effluent Treatment Plant allows us to do is treat and control the activity in the pond water, helping to protect both the workforce and the environment and is a major achievement in its own right."