foamForNuclear: A unified OpenFOAM multi-physics platform for nuclear applications

OpenFOAM has been extensively used to develop dedicated physics solvers for nuclear applications, ranging from thermal-hydraulics to structural mechanics and neutronics. However, existing frameworks still lack a general-purpose structure for coupling arbitrary physics across multiple regions and meshes. This work presents foamForNuclear, a new OpenFOAM-based open-source multiphysics architecture that addresses this limitation. Building on the established GeN-Foam and OFFBEAT codes, the platform introduces a flexible, modular structure that enables users to configure simulations with different combinations of physics, solvers, and coupling strategies without source code modifications. The platform architecture, physics libraries, and verification and validation processes are detailed. Its capabilities and applicability to both fission and fusion systems are demonstrated through selected test cases, including the simulation of the ORNL 19-pin sodium-cooled fuel assembly, the sloshing of liquid metals in pool-type reactors under seismic loading, and the thermal performance of a dual-coolant lithium-lead fusion blanket.