The risk of combustion loads and containment failure deriving from local hydrogen accumulation and potential stratification in containment must be analyzed with three-dimensional simulations covering a full spectrum of severe accident sequences. Probabilistic and deterministic criteria are used to select these accidental sequences. This paper reports on a hydrogen risk sensitivity study based on two Small Break LOCA scenarios, extracted from the PSA Level 2 of a Swiss operating PWR and characterized by a considerable hydrogen production and slow release dynamics. The LOCA accident is evaluated as the limiting sequence for hydrogen release in the short term. Two different break sizes (50 cm² and 5 cm²) are considered in the hot leg. The GOTHIC code is used and a coarse-mesh model was developed to cope with the long transient time. A total of 214 kg hydrogen are released in the 50 cm² SBLOCA scenario. A larger hydrogen mass, overall 470 kg, is discharged in the 5 cm² SBLOCA scenario, characterized by loop failure due to creep rupture in the hot leg. The calculations revealed that a sufficiently large break area leads to the discharge of enough steam to make the containment inert. The highest hydrogen concentrations are at the break location and the actual flammability depends on the amount of steam in the break flow. The final containment atmosphere (without PAR mitigation) shows hydrogen concentration of 4% for the 50 cm² SBLOCA (below the flammability limit) and between 8% and 10% for the 5 cm² SBLOCA, which indicates the potential for flammable states.