Immobilisation challenges with Post Operational Clean Out (POCO) residues

The post operational clean out (POCO) of the highly active liquor storage tanks at Sellafield site will require the removal and immobilisation of residual solids from the heel of the tanks. The solids are expected to contain high levels of molybdenum and zirconium which are insoluble fission by-products. Some of the older highly active liquor storage tanks will require washing and stripping of the compacted solids with an alkali reagent due to a lack of engineered methods of solids agitation, one of the preferred reagents is sodium carbonate solution. Both molybdenum and sodium have limited solubility in the current glass matrix used for immobilisation of high level waste (HLW) in the UK. This project aims to address this issue by developing a new and improved glass formulation and method of delivering the glass forming additives into the existing UK vitrification process. This will ultimately reduce the volume of HLW requiring final disposal and accelerate the high level hazard reduction programme at Sellafield.