Accelerated helium and hydrogen production in 54Fe doped alloys – measurements and calculations for the FIST experiment

F-82H alloys isotopically enriched in 54Fe up to 86% were irradiated in the high flux isotope reactor (HFIR) to determine the accelerated production of helium and hydrogen due to isotopic effects. Results are compared to calculations using isotopic helium production cross-sections from ENDF/B-VI or GNASH and measured neutron spectra. Helium measurements demonstrated an accelerated helium (appm)/dpa ratio of 2.3 after a 1.25-year irradiation, an increase of a factor of 4.3 over natural iron. The accelerated helium production is due to higher helium production cross-sections for 54Fe and 55Fe. Alloys doped with 55Fe could achieve helium/dpa ratios up to about 20, well above the fusion reactor ratio of 10. Hydrogen measurements were performed using a newly developed quadrupole mass spectrometer system at PNNL. Calculations predict that hydrogen production will be accelerated by about a factor of 13 over natural iron. However, measurements show that most of this hydrogen is not retained in the samples.