NDA-RWMD's Letter of Compliance process ensures that radioactive waste destined for the proposed UK Geological Disposal Facility is made passively safe; the main way of ensuring this is the immobilisation of activity in the wasteform. The material most widely used for the encapsulation of the UK's stock of ILW waste is cement due to its chemical stability, compatibility with most wastes, well established physical properties and relatively low-cost. However, there exist some waste streams for which cementation appears unsuitable and so a viable alternative is being sought. Immobilisation of ion exchange resins, reactive metallic wastes and fine particulates such as graphite, are not always suited to cements and are known as "orphan wastes" or "WRATs" (Wastes Requiring Additional Treatment). Babcock is at the forefront of this research in the UK and has recognised the advantages polymeric materials have over grout including the fact that their inert nature leads to the corrosion, expansive cracking and hydrogen generation typically seen within a cementitious waste package being absent if the waste is dry. A number of research and development projects are underway to determine whether a number of WRATs identified in the UK inventory are suited to polymeric encapsulation including the Windscale Piles fuels and isotope waste, GLEEP fuel and Harwell ion exchange
wastes. This article gives an insight into the R&D done so far on polymeric encapsulation both in the UK and around the world.
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