During a severe accident in a PWR reactor, the integrity of the containment can be questioned by the combustion of hydrogen produced by the high-temperature oxidation of the core materials. In order to assess these risks, IRSN is developing an internal software called CALIF3S-P²REMICS to carry out explosion scenarios simulations for hydrogen and for any explosive gaseous mixture. Two different approaches are available for the turbulent deflagration modelling : - In the first one, the turbulence is modelled by a RANS approach. The flame brush location is determined by a G-equation. To handle partially premixed situations, the species mass balances are solved, but reaction rates are expressed from the level-set function. The model is closed by a turbulent flame speed correlation. - The experimental characterization of the velocity field during a deflagration is difficult, especially in large-scale configurations. Moreover, turbulent flame speed correlations assume an equilibrium between turbulence motions and flame surface wrinkling, generally not verified in unsteady flames, and display a large scatter. For these reasons, a LES approach was developed. The combustion model uses a virtually thickened flame formalism combined with a dynamical determination of the sub-grid scale flame wrinkling factors to handle unresolved contributions. Two different configurations of accelerated deflagrations at small and medium scales are investigated. The influence of obstructions (obstacles location or blockage ratio) on the flame propagation is studied. Simulations are performed with both LES and RANS approaches. The aim is to use LES results in order to enhance the RANS model more adapted to large-scale configurations.