Atomistic processes in the evolution of damage in irradiated samples at high temperatures were investigated by linking experimental results to computer simulations. It was proposed that interstitials and their clusters moved to form a group of interstitial clusters which then evolved into dislocations at high temperatures. Vacancies aggregated to stacking fault tetrahedra and voids. At high temperatures, gas atoms did not make a significant contribution to the nucleation of voids at neutron irradiation fluences of the order of 1018/cm2. The stacking fault tetrahedra relaxed, at high temperatures, to give a string of vacancy clusters, within which vacancies were connected 1-dimensionally. The break-up of stacking fault tetrahedra occurred by the jumping of an atom into a stacking fault tetrahedron. A loosely bound vacancy cluster of string-like form moved with an activation energy of 0.2eV. Voids were formed via the coalescence of moving vacancy clusters of string-shape at high temperatures. It was concluded that the role played by gas atoms in the formation of voids was to degrade the mobility of movable vacancy clusters.

Computer Simulation of Void Formation in Neutron-Irradiated Cu and Ni at High Temperatures. Y.Shimomura, I.Mukouda, K.Sugio: Journal of Nuclear Materials, 1999, 271-272, 225-9