The major sources of helium production in stainless steel irradiated in a fast reactor are (n, α) reactions in nickel, iron, chromium, and impurities such as nitrogen and boron. The corresponding reaction cross sections are generally of the threshold type with threshold energies about 1 MeV. Two important exceptions are the cross sections for the two-stage nickel reaction and the boron-10 reaction. Athough lifetime helium concentrations are low, they may be an important consideration, when applying material property change data obtained from the experimental breeder reactor II (EBR-II) core to high-temperature out-of-core fast breeder reactor (FBR) structural components. The ratio of atomic parts per million (appm) helium to displacements per atom is larger for the soft out-of-core spectra than for the harder in-core spectra in which most irradiation data are obtained. These differences should be kept in mind when applying data obtained in EBR-II to FBR out-of-core components.

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This paper reviews the current status and procedures associated with damage function analysis as it applies to the development, design, and operation of nuclear reactors. Damage function analysis provides a systematic applied engineering approach for estimating fluence limits and their uncertainties for neutron-induced property changes for reactor materials and components. A summary of derived, quasi-empirical damage functions is provided and emphasis is placed on the need for standardization in their definition and application. Included is a discussion of the calculation and use of displacement production as an energy-dependent measure of exposure and displacement cross sections for damage function analysis. A brief review is given of the current and projected status of the neutron flux-fluence spectra characterisation that is essential for damage function analysis.