Master equation and Fokker–Planck methods for void nucleation and growth in irradiation swelling

A complete theory of void swelling in irradiated metals requires the treatment of defect cluster nucleation events, as well as subsequent growth of stable clusters. One difficulty is that small-voids evolve rapidly and reversibly, whereas the secular evolution of the overall system is extremely slow. Thus, rate theory models for the void size distribution entail a set of stiff, coupled equations. A combined Master equation and Fokker–Planck numerical approach is introduced to address this problem and permit large time-steps at late times. Calculations are stable in practice, easily converged, and computationally efficient to large doses over a wide range in temperatures. The results are encouraging compared to experiment and earlier, related calculations.