Analysis of burnup performance and temperature coefficient for a small modular molten-salt reactor started with plutonium

In a thorium-based molten salt reactor (TMSR), it is difficult to achieve the pure Th-232-U-233 fuel cycle without sufficient U-233 fuel supply. Therefore, the original molten salt reactor was designed to use enriched uranium or plutonium as the start -ing fuel. By exploiting plutonium as the starting fuel and thorium as the fertile fuel, the high-purity U-233 produced can be separated from the spent fuel by fluorination volatilization. Therefore, the molten salt reactor started with plutonium can be designed as a U-233 breeder with the burning plutonium extracted from a pressurized water reactor (PWR). Combining these advantages, the study of the physical properties of plutonium-activated salt reactors is attractive. This study mainly focused on the burnup performance and temperature reactivity coefficient of a small modular molten-salt reactor started with plutonium (SM-MSR-Pu). The neutron spectra, U-233 production, plutonium incineration, minor actinide (MA) residues, and temperature reactivity coefficients for different fuel salt volume fractions (VF) and hexagon pitch (P) sizes were calculated to analyze the burnup behavior in the SM-SMR-Pu. Based on the comparative analysis results of the bur n-up calculation, a lower VF and larger P size are more beneficial for improving the burnup performance. However, from a passive safety perspective, a higher fuel volume fraction and smaller hexagon pitch size are necessary to achieve a deep negative feedback coefficient. Therefore, an excellent burnup performance and a deep negative temperature feedback coefficient are incompatible, and the optimal design range is relatively narrow in the optimized design of an SM-MSR-Pu. In a comprehensive consideration, P = 20 cm and VF = 20% are considered to be relatively balanced design parameters. Based on the fuel off-line batching scheme, a 250 MWth SM-MSR-Pu can produce approximately 29.83 kg of U-233 , incinerate 98.29 kg of plutonium, and accumulate 14.70 kg of MAs per year, and the temperature reactivity coefficient can always be lower than -4.0pcm/K.