[en] A theory of helium-assisted cavity nucleation in irradiated metals is modified and applied to conditions of continuous helium generation. The theory considers the nucleation and growth of cavities by coprecipitation of vacancies, interstitials, and inert gas atoms. Calculations are performed for type 304 stainless steel for comparison with ion irradiation experiments at approx.= 2 x 10^-4 dpa/s, with helium implantation at the rate of approx.= 10^-2 appm/s, to a total damage of approx.= 5 dpa, over the temperatures 773-973 K. Total cavity number density calculated ranges from 10²³ m^-3 at 773 K to 10²⁰ m^-3 at 973 K. The calculated incubation time for cavity appearance is 1000-3000 s(0.2-0.6 dpa). The calculated plot of cavity density versus time approximately reproduces the experimental data. Predicted cavity size distributions are roughly bell-shaped, but skewed in favor of larger cavity sizes. Calculated and experimental mean sizes agree within a factor of 3. The predictions of the model are found to change very little when most parameters are varied within reasonable limits. The model is, however, found to be strongly sensitive to cavity: matrix surface energy, as well as the rate that helium atoms are displaced from dislocations. (orig.)