A Methodology for Determining the Transmutation Efficiency of Minor Actinides

Abstract

The long-lived minor actinides (MAs) are the major contributors to the long-term radiotoxicity of spent fuel. Therefore, the transmutation of these MAs is considered as an alternative way to the direct disposal. Up to now no definite internationally recognized quantitative criterion of MAs transmutation efficiency was worked out, although this would be highly desirable. The absolute and relative total mass reduction of MAs are completely inadequate. We introduce a new criterion for transmutation efficiency of MAs in nuclear reactors and demonstrate its efficiency by comparing two molten salt reactors; the Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) and the Small Molten Salt Fast Reactor (SMSFR). The proposed criterion takes into account the mass of all useful MAs, short-lived MAs, and short-lived fission products (FPs). The proposed approach merges the advantages of both homogeneous and heterogeneous approaches. We introduce a new approach to load MAs into the SD-TMSR and SMSFR. The change in the actinides and FPs mass has been calculated using SERPENT-2 code. The results show that the transmutation efficiency of 241Am, the prime candidate for transmutation, in the SD-TMSR is much higher than in the SMSFR. After 1500 days of radiation, the transmutation efficiency reaches 82.6% for SD-TMSR, however, for SMSFR it reaches 52.5%.