Intergranular corrosion of irradiated austenitic steels has been attributed to compositional changes produced by radiation-induced segregation at grain boundaries, and the effect has been investigated for the 20Cr/25Ni/Nb stainless steel employed as fuel cladding in advanced gas-cooled reactors. Analytical electron microscopy has been used to determine compositional profiles at grain boundaries in irradiated samples.

The observations are explained in terms of a model based on the inverse Kirkendall effect. At higher doses, interpretation is complicated by grain boundary migration, and compositional changes are found to persist after a boundary has moved away. The compositional profiles are compared with corrosion data for the same irradiated material. Results of Strauss corrosion tests are found to correlate with widths of chromium-depleted zones.

Silicon segregation towards boundaries is a feature of the observations at the lower irradiation temperatures.