THE DEPENDENCE OF HELIUM GENERATION RATE ON NICKEL CONTENT OF FE-CR-NI ALLOYS IRRADIATED TO HIGH DPA LEVELS IN EBR-II

Fusion-relevant helium-effects experiments conducted on austenitic ste els in the Materials Open Test Assembly (MOTA) of the Fast Flux Test F acility (FFTF) fast reactor had to recognize the contributions of both the high neutron energy (n,alpha) reactions and that of the Ni-58(n,g amma) Ni-59(n,alpha) reaction sequence with low energy neutrons. An ex periment conducted in the harder neutron spectra found within the core of Experimental Breeder Reactor-II (EBR-II) has shown that the helium in this reactor was generated almost exclusively from the interaction of high energy neutrons with the natural isotopes of nickel. There wa s very little contribution from Ni-59. The helium production was found to scale directly with the nickel content over the range 25-75% Ni. E ven at very high neutron exposures, the helium production in such reac tors can be predicted within 5% accuracy on the basis of high energy r eactions as demonstrated by an experiment conducted on three Fe-15Cr-N i ternary alloys irradiated to doses of 75-131 dpa in EBR-II. (C) 1998 Published by Elsevier Science B.V. All rights reserved.