Thermodynamically, the oxygen potential of pure steam increases as the pressure increases. As a result, high-pressure steam can produce more highly oxidized urania than can steam at atmospheric pressure. Oxygen-to-uranium ratios as high as 2.60 can theoretically be attained in steam at 150 atm and temperatures near 1600 K. Oxidation to this extent can render the fuel nearly as important a source of hydrogen as the cladding in severe fuel damage accidents. Fuel oxidation by steam, however, is endothermic and provides a heat sink rather than a heat source.