Pure nickel was irradiated in EBR-II without active temperature control to two exposures levels (14 and 31 dpa) at target temperatures of 425, 500, and 600°C in three starting conditions: annealed, 30% cold worked, 30% cold worked and aged at 650°C for 10 hr. The same material conditions were irradiated with active temperature control in FFTF to 33–36 dpa at 430, 520, and 600°C. Post-irradiation density measurements show that in the annealed condition swelling tends to saturate at levels strongly dependent on irradiation temperature. In EBR-II at 600°C. saturation occurs before 12 dpa but swelling is still increasing slowly at 425 and 500°C. The tendency toward saturation of swelling is enhanced by cold working. In addition, the temperature dependence of the saturation level is strongly decreased by cold-working. The maximum swelling under most irradiation conditions is on the order of 8%. In the isothermal FFTF irradiations, the effectiveness of cold working in promotion of swelling is much less pronounced at the higher irradiation temperatures, particular at 600°C. These results are consistent with most evidence from other neutron and charged particle irradiation studies on pure nickel. In comparing the results of these and previous studies, it appears that the saturation is linked to a progressive collapse of the dislocation network when voids begin to dominate the microstructure.