A MOLECULAR-DYNAMICS STUDY OF TEMPERATURE EFFECTS ON DEFECT PRODUCTION BY DISPLACEMENT CASCADES IN ALPHA-IRON

Assessment of the hardening and embrittlement of pressure vessel steel s and welds as a function of neutron dose uses trend curves derived fr om surveillance specimens. For some materials in the UK typical of tho se used in older plant, these curves incorporate an empirical factor t o describe the temperature-dependence of matrix hardening. In the pres ent work, molecular dynamics (MD) simulations have been used to obtain detailed information on defect number and arrangement produced in the primary cascade state of radiation damage as functions of irradiation temperature, T-irr, in alpha-iron. To allow for heat dissipation duri ng the thermal spike phase, the continuum treatment of heat conduction was used to adjust the temperature of the boundary atoms in MD throug hout the cascade process. The continuum parameters were calibrated to match those of the atomic structure, This new hybrid model allows for the variability in form between one cascade and another and has been a pplied to defect generation by cascades of either 2 or 5 keV at 100 K, 400 K, 600 K and 900 K. The effect of T-irr on the production of Fren kel pairs is small but statistically significant: the total number dec reases by about 20-30% as T-irr increases from 100 K to 900 K. The dec rease is smaller than would be consistent with the factor in the trend curves, implying that most of the observed temperature dependence ari ses from postcascade processes. (C) 1997 Elsevier Science B.V.