The response of a typical steel-lined reinforced concrete nuclear reactor containment to postulatedinternal hydrogen detonations is investigated by detailed axisymetric non-linear dynamic finiteelement analysis. The wall pressure histories are calculated for hydrogen detonations using atechnique that reproduces the sharp discontinuity at the shock front. The pressure results can beapplied to geometrically similar vessels. The analysis indicates that the response is more sensitive tothe point of initiation than to the strength of the detonation. Approximate solutions based on a pureimpulse assumption where the containment is modelled as a single-degree-of freedom (SDOF)system may be seriously unconservative. This work becomes relevant because new nuclear reactorsare foreseen as a primary of source of hydrogen supply.