A model for the behavior of Type 304 stainless steel during fast-reactor irradiation has been developed into the computer program SCIM (Swelling and Creep of Irradiated Metals). The model incorporates recent concepts on high-temperature radiation damage into an analytical tool for predicting in-pile behavior of Type 304 stainless steel. Swelling rates are discussed in terms of the relative efficiencies of voids and dislocations as sinks. The calculation for the swelling rate shows it is at maximum when the sink efficiencies are equal. The dose dependence of swelling is found to be a function of the relative rates of void and dislocation loop formation. Saturation mechanisms are discussed with respect to their effect on the swelling rate. Saturation is favored by increased void number density and increased irradiation temperature. This results in a compromise between irradiation temperature and the expected void volume at saturation. Cold work is expected to be increasingly effective with increasing irradiation temperature. At 372°C the dose dependence of swelling in cold-worked material is expected to be much higher than for solution-annealed material because of the rapidly changing relative effectiveness of voids and dislocations as point-defect sinks. High number densities of incoherent precipitate should limit swelling at intermediate irradiation temperatures by forming a saturation microstructure at low void volumes. A climb-controlled in-pipe creep mechanism has been developed. The expression that results depends on the radiation-produced excess interstitial flux to glissile dislocations as the mechanism for enhanced in-pile creep. The glissile dislocations are created by the unfaulting of irradiation-produced interstitial dislocation loops. The principal obstacle is taken as dislocations pinned by the void structure. The maximum inpile creep rate is expected to occur at nearly the same temperature at which swelling is a maximum. The creep rate is expected to decrease slowly with dose.