Synroc and glass composite wasteforms for simulated radioactive waste from advanced reprocessing

• Main Author: Hsieh, Yun-Hao
• Other Authors: Lee, Bill
• Published: Imperial College London 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.754741

A novel advanced reprocessing method, EURO-GANEX, has been developed to further separate wastes, in comparison to the PUREX route, and to enhance the proliferation resistance of reprocessing. It produces a waste-stream that contains fission products only, free of traceable actinides. A Synroc derivative wasteform, Synroc-Z, has been developed to contain minimal host phases for actinides and could immobilise up to 35 wt.% EURO-GANEX waste. Synroc-Z was prepared via hot uniaxial pressing and hot isostatic pressing to compare the phase composition and microstructure. Consolidation of the Synroc-Z by hot pressing techniques resulted in a dense microstructure with low porosity (< 0.5 vol%). Processing temperature was the most important factor in controlling density and phase composition. The suggested hot uniaxial pressing conditions determined from this study are a temperature of 1150-1200oC with pressure of >10 MPa for dwell time of 3 h. Another potential matrix is French borosilicate glass, R7T7, which was prepared via melting vitrification and hot isostatic pressing. However, the applied pressure did not enhance the solubility of Ru, Pd, Te and Mo compared to melting vitrification. The processing conditions, waste loading and surface roughness were varied, and their effects on Synroc-Z durability and microstructure were examined. Synroc-Z samples with dense microstructures displayed similar leach resistance performance and behaviour. Leached samples formed Ti-oxide films and crystals on their surfaces that act as a barrier to mitigate elemental loss. Synroc-Z with low (< 20 wt.%) waste loadings showed slightly poorer durability than Synroc-C while at high (> 20 wt.%) waste loadings, Synroc-Z displayed less degradation in performance compared to Synroc-C. In contrast, the secondary phases formed on the R7T7 glass offer little protection during durability testing as the leach rates of R7T7 displayed only a 1.4 times decrease compared to the 14 times reduction for Synroc-Z between 3 and 28 days.