Damage-function analysis of neutron-induced embrittlement in A302-B steel at 550 F (288 C)

A damage function was derived for neutron-induced increases in the brittle to ductile transition temperature (ΔTT) of ASTM A302-B steel, for temperatures of 550 to 585 F (288 to 307 C). The damage function is a series of weighting factors for the damaging capacity of neutrons of all energy groups in a reactor spectrum that indicate the relative importance of specific energy-group neutrons to the damaging process. The damage function showed that neutrons of energies greater than 1 MeV would account for about 75 percent of the ΔTT, but that neutrons of energies greater than 0.1 MeV would account for over 94 percent for virtually every spectrum evaluated. Furthermore, thermal neutrons were seen to contribute less than 5 percent of the ΔTT, and this only if the thermal population were an order of magnitude greater than the fast neutron population. A method was then developed for plotting neutron fluence (>0.1 MeV) weighted by the damage function that provides excellent correlation of the experimental 550 to 585 F (288 to 307 C) irradiation data for diverse reactor environments. Adequate correlations of data can also be achieved (using only fluences > 0.1 MeV) if conditions preclude inclusion of the damage function. This is a totally rational approach for correlating experimental radiation damage results that has the advantage of being least susceptible to errors in flux spectrum and neutron dosimetry measurements.