Effects of Neutron Spectrum and Dose Rate on Radiation Hardening and Embrittlement in Steels

Abstract

The Kinchin and Pease model for calculating the number of displaced atoms resulting from a fast neutron collision is described briefly and is used to calculate damage rates for iron irradiated in various calculated reactor neutron spectra. It is shown that the results of tension tests on steel specimens irradiated at 150 C in some reactor spectra can be used to determine the importance of energy loss by electronic excitation. The resulting damage function is used to predict the embrittlement of the CALDER HALL reactor pressure vessel steel from the results of accelerated irradiation tests. Preliminary results of investigations of the influence of neutron dose rate show no significant effect on the radiation hardening of mild steel at irradiation temperatures in the range 100 to 350 C. The method whereby the number of displaced atoms produced by thermal (n,γ) reactions can be calculated is described and the importance of this mode of damage relative to that produced by fast neutron scattering evaluated. It is shown that the embrittlement of the CALDER HALL pressure vessel steel is overestimated when both thermal (n, γ) and fast neutron displacements are considered.