Subcascade formation in displacement cascade simulations: Implications forfusion reactor materials

Displacement cascade formation in iron has been investigated by the method of molecular dynamics (MD) for cascade energies up to 40 keV, corresponding to PKA energies up to 61 keV. The results of these simulations have been u sed in the SPECOMP code to obtain effective, energy-dependent cross section s for two measures of primary damage production: (1) the number of survivin g point defects expressed as a fraction of the those predicted by the stand ard secondary displacement model by Norgett, Robinson, and Torrens (NRT), a nd (2) the fraction of the surviving interstitials contained in clusters th at formed during the cascade event. The primary knockon atom spectra for ir on obtained from the SPECTER code have been used to weight these MD-based d amage production cross sections in order to obtain spectrally averaged valu es for several locations in commercial fission reactors, materials test rea ctors, and a DT fusion reactor (ITER) first wall. An evaluation of these re sults indicates that neutron energy spectrum differences between the variou s environments do not lead to significant differences between the average p rimary damage formation parameters. This conclusion implies that the displa cement damage component of radiation damage produced in a DT fusion reactor should be well simulated by irradiation in a fission reactor neutron spect rum, and that differences in nuclear transmutation production may be the pr imary source of uncertainty in the prediction of material performance at hi gh doses in DT fusion reactors. (C) 1999 Elsevier Science B.V. All rights r eserved.