Computing the time dependence of void size distributions during irradiation and annealing

The response of particle size distributions to annealing is described analytically by the Wagner--Lifshitz--Slyosov theory of coarsening. Although the theory has been used to predict void annealing kinetics in irradiated materials, the limits of the model prevent a complete interpretation of the rate controlling mechanisms. These limits are overcome with a numerical solution to the problem for the combined influences of volume diffusion, surface kinetics, and irradiation-induced point defects. A computer program has been written which calculates and updates with time the necessary kinetic and material parameters. The time dependence of the radius distribution function is determined from a finite difference solution to the continuity equation. The program provides wide latitude in simulating and analyzing the dependence of swelling and void growth kinetics on point defect kinetics, point defect sink efficiencies, and variations in irradiation and annealing history. The consequences of including the size distribution in the kinetic analysis are calculated for voids in molybdenum and compared with theoretical predictions of void growth from Brailsford and Bullough and of coarsening from Wagner--Lifshitz--Slyosov theory