A pot-type Liquid-Metal-Cooled Fast Breeder Reactor was analyzed as a civil defense problem in a nuclear attack. In order for the core inventory of fission products to add significantly to casualties, they must be promptly released from the reactor structure due to blast from the weapon, and added to the fallout. The analysis of the interaction of weapon effects with the significant elements of the structure surrounding the reactors was checked by high explosive tests on scale models. It is concluded that for prompt ejection of the core, a megaton-range weapon must be detonated close enough so that the reactor is in the crater, or that an air shock greater than 170 atm impacts at near normal incidence the fueling cell wall crossing the sodium tank. For megaton weapons, delivery accuracy substantially exceeding that ascribed to deployed strategic delivery systems would be required.