Prediction of swelling of 18Cr10NiTi austenitic steel over a wide range of displacement rates

The internal components of pressurized water reactors of Russian types WWER-440 and WWER-1000 are constructed of annealed 18Cr10NiTi steel, a close analog to AISI 321. Void swelling of the internals is a concern for plant life extension and predictive equations are required to assess the potential of swelling in critical components such as the baffle ring or reflection shield that surrounds the WWER core. The only previously available swelling data for this steel were derived at higher than PWR-relevant displacement rates in the BOR-60 fast reactor. The swelling equation previously developed from these data does not incorporate the effect of displacement rate on swelling. Using heavy-ion irradiation at very high dpa rates (10 ⁻² and 10 ⁻³ dpa s ⁻¹) and doses (5–100 dpa) and coupling the results to available neutron data a swelling equation has been developed that specifically incorporates the effect of dpa rate on void swelling. Experimental results allow description of the swelling peak, the incubation period and the steady-state swelling rate over a wide range of irradiation temperature. For the first time it appears possible to describe both ion and neutron data on this steel within the framework of a single empirical model. Swelling maps constructed from this model permit forecasting of the behavior of the steel in WWERs under the required irradiation conditions, not only at already attained exposure doses, but more importantly to higher dose levels that will be reached following plant life extension.