Comparison of calculated helium production in stainless steel due to neutron irradiation with experiment

It is well known that helium produced during neutron irradiation through the (n,α) reaction affects the mechanical properties and the amount of void swelling in nuclear reactor materials. In order to estimate the amount of helium produced in a high alloy stainless steel, which is used in fast reactors and is appropriate to be used in future fusion reactor structural materials, calculations have been performed using the neutron interaction cross sections of the steel constituents. Two austenitic steel specimens of type 1.4970 with high and low boron content, respectively, for which some experimental results are available have been chosen for the present calculations. Predominant nuclear reactions like 10B(n,α)7Li, and the two-step reaction viz. 58Ni(n,γ)59Ni(n,α)56Fe, and the details of the neutron spectrum are taken into account. The cross sections for 59Ni, the major contributor for higher irradiation times, are taken from the KEDAK-4 (German) and the most recent ENDF/B-VI (American) Evaluated Nuclear Data Libraries. The results show that the calculated and the measured estimates differ by a factor of 2 to 3. This difference may be due to uncertainties in the measurement as well as uncertainties in the reaction cross section, especially in the two-step reaction. (orig.)