A full-resolution multiphysics model of the Molten Salt Reactor Experiment

The Molten Salt Reactor Experiment (MSRE), operated at Oak Ridge National Laboratory in the 1960s, was a pioneering effort to demonstrate MSR technology and remains a cornerstone for MSR research. This study presents a full-resolution multiphysics model of the MSRE, resolving the entire reactor vessel and internal structures without porous-media or axisymmetric approximations. The workflow couples Monte Carlo neutron–photon transport (Serpent 2) with conjugate heat transfer and turbulent flow simulation (GeN-Foam within the foamForNuclear platform) on unstructured meshes, iterated to convergence with temperature and density feedback. Predicted effective multiplication factor and power fractions show good agreement with benchmark data, and velocity profiles in the volute, annulus, and core passages are compatible with experimental measurements and previous simulations within known uncertainties in geometry and operating conditions. Where design parameters are uncertain, the model demonstrates the ability to infer missing data from experimental observations, highlighting the potential for high-fidelity simulation techniques to support reactor start-up procedures and digital-twin applications. The model reproduces major experimental flow trends in the lower plenum while revealing three-dimensional structures that axisymmetric surrogates cannot capture. Some discrepancies remain, largely attributable to input uncertainties and limitations of RANS models under strong adverse pressure gradients, suggesting future extensions to LES turbulence modeling. • Developed a full-resolution multiphysics model of the MSRE. • Implemented cell-by-cell two-way coupling of Serpent 2 with GeN-Foam. • The model reproduces key experimental flow trends. • The model reveals three-dimensional flow structures not captured by simplified studies. • Results underscore the importance of resolving geometric details for MSR design and analysis.