Immobilisation of Prototype Fast Reactor raffinate in a barium borosilicate glass matrix

Abstract

The vitrification of Dounreay Prototype Fast Reactor (PFR) Raffinate in a barium borosilicate glass matrix was investigated, with the aim of understanding process feasibility and the potential benefits over the current baseline of cement encapsulation. Laboratory scale glass melts demonstrated the production of homogeneous glasses incorporating at least 20 wt% simulant PFR waste (on an oxides basis), with no detectable crystalline accessory phases. The hardness and indentation fracture toughness of the simulant PFR waste glasses were determined to be comparable to those of current UK high level waste glass formulations. The normalised dissolution rate of boron from the simulant PFR glasses was determined to be 3 × 10−2 g m-2 d-1, in 18.2 MΩ water at 90 °C and surface area/volume ratio of 1500 m−1, only a factor of two greater than the French SON-68 simulant high level waste glass, under comparable conditions. Consequently, the simulant PFR waste glasses show considerable promise for meeting envisaged waste acceptance criteria for geological disposal. Overall, the superior stability of vitrified PFR wasteforms could enhance the safety case for long term near surface storage of radioactive wastes, mandated by current Scottish Government policy.