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 similar to 6 x 10(14) similar to 7 x 10(15), and similar to 8 x 10(16) n m(-2) s(-1) (E > 1 MeV) to fluence levels ranging from similar to 6 x 10(21) to similar to 7 x 10(22) n m(-2) (E > 1 MeV) at temperatures of about 50 degrees C to 150 degrees C in the Japan Materials Testing Reactor (JMTR). The results showed that the radiation-induced increases in ductile-to-brittle transition temperature (Delta DBTT) at a neutron flux level of similar to 6 x 10(14) were greater than those for neutron flux level of similar to 7 x 10(15) n m(-2) s(-1). The neutron flux effect on embrittlement tended to be more pronounced in the lower neutron fluence range of similar to 6 x 10(21)-similar to 1 x 10(22) n m(-2) than in the higher fluence level of similar to 7 x 10(22) n m(-2), and also to be larger for the low copper steel than for the high copper steel, although the Delta DBTT 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 Delta DBTT 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. (C) 1999 Elsevier Science B.V. All rights reserved.