Liquid-fueled molten salt reactors (MSRs) are characterized by the use of liquid nuclear fuel, which leads to a unique thermal-hydraulic phenomenon in the core involving the simultaneous occurrence of nuclear fission heat generation and convective heat transfer. This distinctive behavior creates a critical need for high-fidelity experimental data on internally heated flows, yet such studies are severely constrained by the lack of methods to generate controllable, high-power-density volumetric heat sources in fluids. To address this methodological gap, this study proposes and numerically investigates a novel experimental concept based on microwave heating. The design features an innovative multi-tier hexagonal resonant cavity with fifteen strategically staggered magnetrons. A comprehensive multi-physics model was developed using COMSOL Multiphysics to simulate the coupled electromagnetic, thermal, and fluid flow processes. Simulation results confirm the feasibility of generating a volumetric heat source, achieving an average power density of 6.9 MW/m³. However, the inherent non-uniformity in microwave power deposition was quantitatively characterized, revealing a high coefficient of variation (COV) for power density. Crucially, parametric studies demonstrate that this non-uniformity can be effectively mitigated by optimizing the flow channel geometry. Specifically, using a smaller diameter tube or an annulus pipe significantly improved temperature field uniformity, reducing the temperature COV by over an order of magnitude, albeit at the cost of reduced absorption efficiency. Preliminary discussion also addresses the extension of this approach towards molten salt experiments. The findings establish a practical design framework and provide quantitative guidance for subsequent experimental investigations into the thermal-hydraulic behavior of internally heated fluids, offering a promising pathway to support the design and safety analysis of liquid-fueled MSRs.

The existing thermal neutron molten salt reactor design has a complicated online processing system that has many technical difficulties. A thorium-based molten salt fast energy amplifier (TMSFEA) driven by a proton accelerator can operate stably for nearly 40 years at a rated thermal power of 300 MW without online processing. In order to simplify the core structure of TMSFEA, the core design is based on a hollow and moderator-free cylindrical geometry. The molten salt in the core serves as both fuel salt and spallation target. In this paper, based on the previous TMSFEA core neutron physics design, the core thermal-hydraulic design principles of TMSFEA are proposed, and a detailed core design with specific core structures as well as three-dimensional core thermal-hydraulic performance are obtained. Through computational fluid dynamics steady-state analysis, the arrangement of the core inlet and outlet and the shape of the core sidewall are optimized. Suitable distribution plates and skirt plates are proposed, and two corresponding lower plenum structures are designed to improve the flow field in the core. This study provides TMSFEA with core structures that meet the thermal-hydraulic design principles and also provides ideas for similar hollow reactor core designs.