During a severe accident in a watercooled nuclear power plant, large quantities of hydrogen can be generated in the reactor core. The hydrogen mixed with air presents a potential risk of combustion when the hydrogen concentration reaches flammability limits. If combustion occurs, pressure loads can damage safety systems and even compromise the structural integrity of the nuclear reactor walls. Thus, predicting the pressure loads is an important safety issue to ensure the reliability of critical structures in the event of a severe accident.

Computational Fluid Dynamics (CFD) codes can be used as numerical tools to assess the risks of hydrogen combustion and predict detailed transients of the pressure loads. The scenarios simulated in nuclear safety engineering can be analyzed with low fidelity models based on reduction assumptions of the physical phenomena. Specifically, the flame gradient models are chosen to model the combustion phenomena based on a turbulent flame speed to which the combustion propagates. In this work, the applicability and robustness of a pressure-based solver for compressible reacting flows is first assessed through the canonical Sod shock tube problem, thereby establishing its capability to handle a wide range of Mach numbers relevant to deflagration and mild shock regimes. Building upon the baseline XiFoam solver, two new solvers are introduced: NRGXiFoam for fully premixed conditions, and ppNRGXiFoam for partially premixed configurations. A central contribution of this thesis is the optimisation,
modification, and integration of a generic laminar flame speed library into OpenFOAM, enabling robust predictions for lean hydrogen-air mixtures across a wide range of conditions.

The ppNRGXiFoam solver extends the fully premixed framework by incorporating transport equations for the mixture fraction and its variance, thereby enabling the simulation of fuel stratification effects. The updated flame speed library is validated against experimental data for lean stratified hydrogen–air flames, and its interaction with turbulence closures is assessed through different algebraic wrinkling factor models.

Validation and performance assessment are carried out on two experimental configurations ENACCEF and the ENACCEF-2 flame acceleration facilities with obstacle-induced turbulence. Key quantities such as flame radius, turbulent flame speed, and pressure rise are compared to experimental data, with sensitivity studies performed on mesh resolution, time-stepping, and turbulence model selection.

Overall, the developments presented in this thesis significantly enhance the predictive capability of OpenFOAM for partially premixed hydrogen combustion under conditions relevant to nuclear safety, while providing a validated and flexible framework for modelling turbulent flame propagation with composition inhomogeneities.