Phase Separation and Crystallisation in UK HLW Vitrified Products

Given the complex composition of the UK High Level nuclear Waste (HLW) streams and the single base glass frit composition used to vitrify these streams, some phase separation and/or crystallisation in the vitrified product is almost inevitable. Depending upon the specific composition(s), the presence of phase separated/crystalline material can be deleterious, inconsequential or even advantageous to the quality of the product. It can also determine (or be determined by) the operational plant parameters for HLW glass manufacture.This paper focuses on HLW product glasses manufactured on the Vitrification Test Rig, a full scale non-active vitrification plant based on the Atelier de Vitrification de La Hague process. The influence of processing conditions, waste stream composition and overall waste loading on the phase separation/crystallisation in historical and current vitrified products are discussed. The implications of future changes to waste stream constituents along with a potential move to an alternative base glass formula are also explored.