Comparison of the swelling produced in nickel by neutron irradiation and by ion bombardment

Ion bombardment is a useful tool for investigating the swelling behavior of candidate alloys for LMFBR cladding and duct applications because high doses can be attained in a matter of hours. There are, however, several questions which must be answered to increase the utility of the technique. Of major concern is the similarity in void nucleation and growth processes under neutron irradiation and under charged particle irradiation. The difference in damage production rate of some four orders of magnitude produces a change in the temperature dependence of swelling and may also influence the magnitude of the swelling. Differences in the cascade structure of the damage produced by charged particles and neutrons may also influence the results. A few comparisons of swelling produced by charged particles and by neutron irradiation at high doses have been made for technological materials. These results show that the incubation period for swelling to develop and the temperature shift for dose rate are both influenced by alloy composition, heat treatment, and stability. It is therefore desirable to study the phenomena in a pure material so as to separate the effects arising from alloy composition and stability from those inherent to the basic damage process. The swelling behavior of pure nickel has been extensively studied at NRL to characterize the influence of temperature, dose rate, and dose on the nucleation and growth of voids under ion bombardment. Observations are reported of the swelling behavior of pure nickel of the same stock under neutron irradiation in EBR-II and these observations are compared with the previous ion bombardment results