Mitigating re-circulation zones in small modular Molten Salt Fast Reactor models

Molten Salt Fast Reactors (MSFRs) utilize liquid fuel. The fuel itself is cooling the reactor as well as generating the power. The EVOL design was selected as the base reactor, which has homogeneous fuel flow. When the reactor dimensions are reduced to Small Modular Reactor (SMR) scales, re-circulation zones start to form. The existence of these zones disrupts flow homogeneity. The disruption affects the neutronic behavior of the reactor. This study aims to mitigate these re-circulation regions by optimizing the reactor geometry for uniform flow distribution. Various geometric modifications, including different inlet configurations and wall curvatures to the EVOL design, were investigated through Computational Fluid Dynamics simulations. A final 6-inlet, 6-outlet sm-MSR model was developed. The developed model does not need additional mixing devices or complexity (such as diffusers, guides, etc.). Steady-state thermal-hydraulic analyses were conducted using a 3D-CFD approach with the Standard k-epsilon turbulence model. The power distribution within the core was modeled using a cosine-based source term to capture the effect of temperature distribution. Mesh sensitivity studies ensured high-quality discretization in regions that are susceptible to re-circulation. 1-2.5 million mesh counts were analyzed for the mesh sensitivity on average temperature. 1 million mesh count was found to be sufficient for the analysis. The current design allows sm-MSR to work with 90o temperature margin. The results demonstrate that the optimized design eliminates re-circulation zones ensuring homogeneous flow, thus enhancing mixing and maintaining homogeneous temperature distribution. This also prevents excessive thermal stress on the blanket. The findings contribute to the development of compact MSFR designs. Future work will focus on transient analysis and further optimization of thermal-hydraulic parameters.