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Dewatering Hazardous and Radioactive Sludges

03.06.2014  |  

Radioactive sludges are an issue for many parts of the nuclear sector; they can be found in ponds, in vessels and in pipework. They present real problems for operational and decommissioning teams and the removal and recovery of these sludges can be quite challenging.

We have been working on this issue with sludges since 2009; our first experience being on the Chapelcross site where certain drains within the ISB section of the site needed to be cleaned but the material in the drains was potentially contaminated. Since that time we have added to our technology know-how and demonstrated sludge removal, processing and drying at Chapelcross, Sellafield and LLWR sites.

There are several issues to overcome to successfully treat sludge; these are:

1) recovering the sludge in a useable form,

2) reducing the water content of the recovered sludge/ suspension and

3) removing sufficient water from the sludge so that it may be disposed of as a dry material.

It’s not easy to remove sludge from vessels; in all cases energy must be put into the system to extract the sludge and place it in a holding vessel. Sludges have different compositions but we find that they have a common characteristic; any energy input into a sludge system will tend to change the surface chemistry of the particles that form the sludge and create suspensions rather than discrete solid: liquid systems; of course, given enough time the suspension will revert to a solid:liquid system. It’s not always possible to wait that long.

We take the raw sludge from the vessel, this can be done by pumping or by eductor transfer, typically at this stage the sludge is less than 1% by weight solids content. Raw sludge is treated with poly electrolytes and flocculating agents to overcome the surface charges; this creates a forced deposition and it also produces a thickened sludge with a solids content of perhaps 15% solids. We take this thickened sludge and process it further. The liquid left after the thickening process is clarified and can be re-used to recover more sludge or disposed of by an appropriate route.

The thickened sludge is transferred to the final treatment stage. We use permeable containers to hold the sludge and then apply a small electrical potential across the sludge; this produces a remarkable drying effect for a very small cost; for example we have dried thickened sludge from 85% water content to below 25% levels in less than 72 hours. When a sludge is dried to 25% water content it is suitable for disposal to landfill or it could be grouted or treated in other ways.

The technology we use is modular and is commercially available, we put together the elements that are needed for each project; as such each project receives a bespoke solution. We have demonstrated the technology on VL an LL wastes and the technology could well have potential for use inside cells as all of the treatment steps can be contained within a cell whilst the control equipment can remain outside.

If you have a sludge removal issue then we would be delighted to have a discussion about the project. You can contact us on 01900 870140.