In a core disruptive accident in a liquid-metal fast breeder reactor, rearrangement of core materials may lead to a prompt critical excursion. Damage to the primary containment, especially the head seals and head bolts, caused by the subsequent core disassembly is a primary concern of hypothetical accident analysis. A systematic study has been performed to evaluate the sensitivity of that damage in a commercial size reactor to various uncertainties. The damage is very insensitive to the equation-of-state of the fuel but highly sensitive to the reactivity ramp rate through prompt critical. From the point of view of vessel damage calculations, these results indicate that there is little incentive to improve our equation-of-state data on unirradiated mixed-oxide fuel.