The transition from established system codes to higher-fidelity, three-dimensional multi-physics platforms is a central challenge in modern nuclear reactor analysis. The deployment of advanced simulation tools in nuclear reactor physics demands systematic validation against well-characterised experimental reference cases before they can be trusted for design and safety analysis. This thesis, conducted within Work Package 2 of the EU-funded EVEREST project, contributes to that effort by applying and validating foamForNuclear — an open-source multi-physics platform built on the OpenFOAM framework — to the Budapest University of Technology and Economics (BME) Training Reactor, a 100 kW pool-type facility operated under natural circulation conditions, in the context of the present study.