Energy Deposition Mechanism and Distribution Characteristics in a Liquid Fuel Molten Salt Reactor Under a Static Fuel Salt Approximation

Accurate specification of spatial heat sources is required for liquid fuel molten salt reactors, given the redistribution of deposited energy among fuel salt, graphite, and metallic structures by gamma ray transport. In this study, a refined power deposition framework based on Monte Carlo particle transport was formulated for a 150 MW thorium molten salt reactor to quantify particle, material, and spatial contributions to the core heat source. The calculation was performed under a static fuel salt approximation, in which flow-induced transport of delayed particle precursors in the circulating fuel salt was not explicitly considered. Particular attention was given to gamma ray generation, transport, and deposition, as well as to the resulting refined power density distribution. The results show that gamma rays contribute 7.64 MW to graphite heating, approximately 3.11 times the neutron contribution. In the alloy sleeve, capture gamma rays account for 63.44% of the deposited power, producing an average power density of 9.34 MW/m3, nearly 18 times that in graphite. This behavior is primarily associated with the strong neutron capture capability of the tungsten bearing alloy and the relatively short gamma ray mean free path in this material. The refined power density distribution further indicates that fuel salt channel power density decreases from about 100.0 MW/m3 near the core center to 57.7 MW/m3 near control rod assemblies, while local graphite power density varies by more than 40%. These findings indicate the need for spatially resolved and material specific heat source descriptions in thermal hydraulic coupling and structural heat load assessment, rather than material averaged treatments or fixed fuel to graphite scaling.