Radioactive Waste Management in U/Th Fuel Cycles

Abstract

Radioactive waste streams are generated at various stages of uranium and thorium fuel cycles. Treatment and storage/disposal of low and intermediate level wastes (LILW) from U fuel cycle are being practiced in various countries, which have adopted either open or closed fuel cycles for nuclear power generation. The spent nuclear fuel (SNF) from open fuel cycle is being stored. In the case of processing of SNF for closed fuel cycle, the resultant high-level liquid waste (HLW) is solidified by immobilization in an inert matrix like glass, and stored in engineered facilities. The research and development work is being pursued in various countries on disposal of SNF and solidified HLW in deep geological formations. In the case of thorium fuel cycle, since the mining is generally in shallow sea coastal areas, the waste generation is comparatively less. Process and technology for treatment and disposal of the wastes generated during mining and milling of monazite for recovery of thorium and associated rare earth (RE) elements is well established. Waste management practices with respect to the waste generated in fabrication of Th-based fuel and in operation of Th-fuelled reactors will not be much different from similar uranium fuel-based facilities. However, in the immobilization of HLW from the reprocessing of Th-based SNF, some challenges are likely on account of difficulty in dissolution of thorium oxide in concentrated nitric acid which necessitates the use of fluorides and aluminum. The results of R&D on the aspects of reduction of concentration of fluorides and aluminum in the waste, incorporation of thorium oxide in boro-silicate glass matrix, and its impact on the characteristics of vitrified waste product (VWP) as well as future areas of research are discussed in this chapter.