[en] The MARCH and HECTR computer codes are used in this study to examine hydrogen production, transport, and combustion in an ice-condenser containment for a number of hypothesized severe accidents. Both degraded-core and core-meltdown accidents are treated. The sensitivity of the containment pressure-temperature response is assessed for a number of factors, including the hydrogen and steam source-term assumptions, ignition and propagation limits, combustion completeness, flame speed, spray operation, and recirculation fan operation. The highest containment pressures occur for those cases where the igniters are assumed to fail, the recirculation fans or containment sprays are assumed to fail, or very large steam and hydrogen releases accompanying vessel breach are predicted