Preliminary Development of an Open-Source One-Way Steady-State Monte Carlo Neutronics-CFD Coupling Framework Using OpenMC and OpenFOAM

A coupled neutronics-thermal-hydraulic simulation framework based on OpenMC and OpenFOAM is developed and verified for pressurized water reactor (PWR) applications. The framework enables the transfer of spatially resolved fission power distributions from Monte Carlo neutronics calculations to a computational fluid dynamics (CFD) solver for thermal-hydraulic analysis. The coupling methodology is assessed using a hierarchical set of test cases, from a simplified pin-cell configuration to a full-height 3×3 PWR assembly with a 3.5-m active core. The performance of the power-mapping and interpolation strategy is examined through axial and cross-sectional comparison, demonstrating preservation of key spatial characteristics of the neutronics heat source across extended domains. Coupled simulation predicts physically consistent temperature, density, and velocity fields in the fuel, cladding, and coolant. It captures the expected axial trends, rod-bundle flow behaviour, and boundary-condition effects. The framework remains stable when scaled to multi-pin geometries and greater axial extent. The thermal-hydraulic responses reflect the imposed neutronics source. The results demonstrate that the OpenMC-OpenFOAM coupling approach offers a reliable, scalable platform for integrated reactor simulations, enabling application to larger, more complex configurations for thermal-hydraulics and safety analysis.