Multiphysics assessment of a graphite moderated molten salt reactor

Molten Salt Reactors have gained renewed interest due to their potential advantages compared to conventional reactors based on solid fuels; these include passive safety features, low-pressure operation, large negative feedback coefficients and the possibility for online fuel reprocessing. The tightly coupled neutronics and thermal-hydraulics properties of the liquid-fueled reactors, however, necessitates the development of new multiphysics simulation tools. In this study we present results from the SEALION multiphysics code. The SEALION code employs a specialized thermal hydraulics solver based on the finite volume computational fluid dynamics code OpenFOAM, coupled with a custom-made Point Kinetics neutronics solver, that explicitly accounts for the altered neutron importance due to delayed neutron precursor decay and transport. The main advantage of this approach is that it allows for a pre-determination of the temperature feedback using Monte-Carlo codes like Serpent2. Despite the reduced order reactor physics modeling, point kinetics solvers are expected to capture the physics of lower-order transients and still are being used extensively in nuclear reactor transient analysis for solid-fueled reactors. It is therefore of interest to expand and evaluate point kinetics methods for liquid fueled reactors. To validate the SEALION code, results of a sub-channel model are compared to data available from the Molten Salt Reactor Experiment (MSRE). Specifically, fuel and graphite temperature profiles and fuel velocity fields are reactivity insertion derived for steady state operation. A simple transient scenario of a step reactivity insertion is modeled and the reactivity feedback of the system evaluated.