Effect of neutron flux on low temperature irradiation embrittlement of reactor pressure vessel steel

Miniature Charpy V-notch impact test specimens of commercial reactor pressure vessel (RPV) steels having high and low copper contents were irradiated at the different irradiation positions with neutron flux levels of ∼6×1014, ∼7×1015, and ∼8×1016 n m−2 s−1 (E>1 MeV) to fluence levels ranging from ∼6×1021 to ∼7×1022 n m−2 (E>1 MeV) at temperatures of about 50°C to 150°C in the Japan Materials Testing Reactor (JMTR). The results showed that the radiation-induced increases in ductile-to-brittle transition temperature (ΔDBTT) at a neutron flux level of ∼6×1014 n m−2s−1 were greater than those for neutron flux level of ∼7×1015 n m−2 s−1. The neutron flux effect on embrittlement tended to be more pronounced in the lower neutron fluence range of ∼6×1021–∼1×1022 n m−2 than in the higher fluence level of ∼7×1022 n m−2, and also to be larger for the low copper steel than for the high copper steel, although the ΔDBTT for the high copper steel was larger than that for the low copper steel regardless of neutron fluence or flux. The displacement dose rate effect identified by the data converted to the ΔDBTT for the full size Charpy specimens from those for the miniature Charpy specimens was consistent with that based on the comparison of the results in the literature.