12th International Symposium on Symbiotic Nuclear Power ( ISSNP-2026)

Molten Salt Reactors (MSRs) are promising Generation IV systems offering inherent safety, online fuel processing, and efficient heat utilization. However, their development remains constrained by limited experimental data, prototype experience, and materials capable of withstanding extreme operating conditions. In this context, high-fidelity multiphysics modelling is essential for predicting reactor behavior, evaluating performance under challenging operating conditions, and supporting the design and development of advanced MSR concepts. This work investigates the use of OpenMC-generated group cross sections in Moltres, a MOOSE-based multiphysics application for coupled neutronics and thermal-hydraulics analysis of liquid-fuelled MSRs. Neutronics and thermal-hydraulics models were developed for the Oak Ridge Molten Salt Reactor Experiment (MSRE) and Seaborg Technologies’ Compact Molten Salt Reactor (CMSR), with OpenMC-generated cross sections used for the coupled simulations. The results were compared with previously published Moltres simulations based on Serpent-generated cross sections and showed good agreement, demonstrating the suitability of OpenMC for cross-section generation in MSR multi-physics analysis. Full-core coupled simulations were performed to evaluate neutron flux, power density, effective multiplication factor, delayed-neutron precursor transport, and temperature-dependent reactor behavior. The results demonstrate that Moltres, coupled with OpenMC-generated cross sections, provides a capable framework for steady-state MSR analysis and core design. The study also identifies potential design improvements for the MSR while highlighting uncertainties associated with nuclear data and modelling assumptions. Overall, this work demonstrates the potential of OpenMC–Moltres coupling as a valuable computational framework for the analysis and further development of MSRs.

Multiphysics coupling,Neutronics,Thermal hydraulic