Abstract
The evolution of helium-filled cavities during neutron irradiation is analyzed in terms of the stochastic theory of atomic clustering. The conventional separation of nucleation and growth is replaced by a self-consistent evolution model. Starting from kinetic rate (master) equations for the clustering of helium and vacancies, helium mobility, helium-vacancy cluster stability, and cavity nucleation and growth are all included in the model. Under typical fusion irradiation conditions (cascade damage and high helium-to-dpa ratios), the following is suggested: (1) Helium mobility decreases with the evolution of the microstructure. At quasi-steady state, it is mainly controlled by interstitial replacement or thermal desorption. (2) Gas re-solution from cavities by cascades increases nucleation at high fluences. (3) The cavity size distribution is broadened because of cascade-induced fluctuations. (4) The majority of helium-filled cavities are in a nonequilibrium thermodynamic state.
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