Preliminary study on TRUs utilization in a small modular Th-based molten salt reactor (smTMSR)

Small modular reactors (SMRs) can provide an energy option with low carbon emission, enhanced safety conviction, convenient construction and operation. Meanwhile, molten salt reactors (MSRs) have been recognized as one of the reference reactors of the Generation IV International Forum (GIF) with the unique potential (inherent safety, no fuel fabrication, online fuel reprocessing, etc). Combining advantages of SMRs and MSRs, the small modular Th-based molten salt reactor (smTMSR) has excellent performances such as inherent safety, economics, sustainability, and proliferation resistance. Moreover, thorium is still an attractive fuel in a smTMSR with characteristics of online refueling and reprocessing. In this paper, we attempt to study the capability of the transition to thorium fuel cycle in a thermal smTMSR by analyzing the neutronic characteristics using TRUs as starting fuel. Optimizations are conducted to produce the required amount of U-233 for starting a new smTMSR based on various fuel fractions in thermal energy region. It is concluded that the U-233 production is superior with higher fuel fraction in the core, which indicates that a thermal smTMSR with a proper fuel fraction can achieve the transition to thorium fuel cycle. The HM and Pu mole proportions which may have a negative influence on the molten salt stability are analyzed. Moreover, the temperature feedback coefficient as a key safety parameter is also discussed. With a suitable fuel fraction in thermal region, the smTMSR can well satisfy the restrictions of HM and Pu mole proportions and safety demands.