A postulated severe accident in a nuclear power plant (NPP) can lead to generation of large quantities of hydrogen in the NPP containment. Potential hydrogen combustion and ensuing dynamic pressure loads can be detrimental to the integrity of the containment and its structure, systems and components. This paper provides validation results of a computational fluid dynamics (CFD) modeling approach based on two combustion models, that is the Turbulent Flame-speed Closure (TFC) model and the Extended TFC (ETFC) model. The latter was further elaborated in order to investigate the influence of the laminar flame speed on the flame evolution and propagation modeling. As a result, a newly developed approach in form of the augmented ETFC model was introduced and validated as well. The hydrogen slow deflagration results from the Upward Flame Propagation Experiment (UFPE) conducted in the large-scale HYKA-A2 experimental facility have been used for validation. The main results of the performed validation are presented and discussed, with the focus on axial and radial flame front propagation, maximum pressure, pressure increase rate and flame front development.