Verification of multiphysics coupling techniques for modeling of molten salt reactors

Crucial to the development of molten salt reactor (MSR) designs is the application of multiphysics codes to model the tightly coupled neutronics and thermal-hydraulics behaviour of the liquid fuel. However, the verification and validation of such codes is not a trivial task, in particular for fast reactor designs, where no experimental data are available. In absence of experimental data, a benchmark was developed by LPSC/CNRS-Grenoble for multiphysics codes dedicated to MSR studies. In this study we present two independent multiphysics approaches and apply them to this benchmark. The first approach utilizes the Serpent2 multiphysics interface, allowing for high fidelity coupling of the finite volume computational fluid dynamics code OpenFOAM and Serpent2. In this approach, Serpent2 serves as the neutronics solver and is coupled to an OpenFOAM based thermal-hydraulics solver and supplemented by a delayed neutron precursors transport solver implemented in OpenFOAM. The main advantage of this coupling approach is that it allows for using a high accuracy Monte-Carlo approach to solve the neutron transport equations. The second approach is a novel approach that utilizes the SEALION framework. The SEALION code employs a specialized thermal hydraulics solver based on OpenFOAM, coupled with a custom-made modified point kinetics neutronics solver, that explicitly accounts for the altered neutron importance due to the transport of delayed neutron precursors. The main advantage of this approach is that it allows for a pre-determination of the temperature feedback effects using Monte-Carlo codes, such as Serpent2. Both approaches are verified against results from the benchmark and the overall agreement between the results demonstrates the validity of both approaches.