The severe reactor accident at Fukushima Daiichi Nuclear Power Plant (2011) has confirmed the need to understand the flow and transport processes of steam and combustible gases inside the containment and connected buildings. Over several years, Computational Fluid Dynamics (CFD) models, mostly based on proprietary solvers, have been developed to provide highly resolved insights; supporting the assessment of effectiveness of safety measures and possible combustion loads challenging the containment integrity. This paper summarizes the design and implementation of containmentFOAM, a tailored solver and model library based on OpenFOAM^®. It is developed in support of Research & Development related to containment flows, mixing processes, pressurization, and assessment of passive safety systems. Based on preliminary separate-effect verification and validation results, an application oriented integral validation case is presented on the basis of an experiment on gas mixing and H₂ mitigation by means of passive auto-catalytic recombiners in the THAI facility (Becker Technologies, Eschborn, Germany). The simulation results compare well with the experimental data and demonstrate the general applicability of containmentFOAM for technical scale analysis. Concluding the paper, the strategy for dissemination of the code and measures implemented to minimize potential user errors are outlined.

As the applications of hydrogen as a replacement for fossil fuels and energy storage increase, more concerns have been raised regarding its safe usage. Hydrogen’s extreme physical properties—its lower flammability limit (LFL), for instance—represent a challenge to simulating hydrogen leakage and, hence, mitigating accidents that occur due to such leakage. In this work, the OpenFOAM-based CFD simulation package containmentFOAM was validated by different experimental results. As in its original use, to simulate nuclear safety issues, the containmentFOAM package is capable of capturing different phenomena, like buoyant gas clouds and diffusion between gases and air. Despite being widely validated in nuclear safety, this CFD package was assessed with benchmark experiments used to validate hydrogen leakage scenarios. The validation cases were selected to cover different phenomena that occur during the hydrogen leakage—high-speed jet leakage, for example. These validation cases were the hallway with vent, FLAME, and GAMELAN experiments. From the comparison of the experimental and simulation results, we concluded that the containmentFOAM package showed good consistency with the experimental results and, hence, that it can be used to simulate actual leakage cases.