The radiation swelling of samples of fuel element cladding made of steel 16Cr-15Ni-2Mo-lMn after its use up to a maximum damage dose 73 – 93 dpa in the reactor BN -600 was studied. The samples were cut out from areas of different location in the core, so the irradiation temperature of various samples varied from 390 to 610 °C. The damage dose varied from 40 –92 dpa and the radiation damage rate varied from 0.9 ∙ 10-6 to 2 ∙ 10-2 dpa/s.
The conditions necessary to have the radiation swelling occurred were considered theoretically within the statistical thermodynamics of solids. An analytical expression connecting the incubation period of swelling with a temperature, fluence, radiation damage rate, and characteristics of material microstructure was obtained. The swelling rate at the post-incubation stage at various irradiation temperatures was estimated. The character of swelling dependencies on temperature, dose, and radiation damage rate obtained from the experimental data agreed well with the results of the theoretical analysis. In the range of 390 to 600 °C the nucleation damage dose initiating swelling increased with irradiation temperature. The swelling rate in the post-incubation phase also increased. Decreasing radiation damage rate shifted the fluence dependence of swelling into a region of lower fluences and temperatures.