Neutron energy spectrum and temperature effects on freely migrating defectconcentrations and grain boundary segregation in alpha-Fe

Molecular dynamics (MD) calculations of cascades in alpha-Fe are used to pr edict the concentration of freely migrating defects. The single self-inters titial atoms (SIAs) are recognised to be important because they are more re mote from the cascade and their migration energies are less than those of s ingle vacancies. We are therefore able to estimate the enhanced concentrati on of freely migrating interstitial defects as a function of: (1) neutron e nergy spectrum, and (2) temperature. We compare our predictions with those obtained by diffusion experiments. The algorithms describing the temperatur e effect for a given neutron energy spectrum are incorporated in the models for radiation induced grain boundary segregation of P in alpha-Fe to produ ce an improved prediction of the temperature dependence of the segregation. Comments will be made on the implications of the new P segregation predict ions for ferritic steels and on the importance of the low energy part of th e neutron energy spectrum in determining freely migrating defect population s. (C) 1999 Elsevier Science B.V All rights reserved.