Void Swelling as a Stochastic, Evolutionary Process

Past theories of radiation swelling have mostly dealt with the effect of void growth on the steady-state rather than of void nucleation on the incubation of swelling. However, new analysis indicates that incubation and its dependence on dose rate, impurity concentrations. and temperature dramatically influences the cumulative experimental swelling. We present rate theory calculations of this void nucleation and growth that include the time-dependent coupling and evolution of point defect concentrations, void size distribution, and dislocation density. A transient, swelling-free period originates in the exponential sensitivity of nucleation to the temperature and point defect supersaturations and the dependence of the defect concentrations on the dose rate, temperature, and aggregate sink strengths. Specifically. simulations representing cold worked pure metals show delayed swelling that is governed by dislocation evolution towards a reduced. steady-state density. Impurity atoms are expected to affect the incubation period through the initial dislocation density and subsequent rate of evolution. We conclude that appreciable void swelling requires a sufficiently low concentration of network dislocation and dislocation loop sinks, and that incubation is the time required to achieve this state