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Neutron irradiation damage is a key factor that influences behaviors of nuclear materials. Folding the specific neutron flux to the pre-calculated displacement damage cross section is a widely used method for quantifying neutron irradiation damage in nuclear reactors. This method has been implemented in various neutron transport codes, such as ERANOS and OpenMC. However, because the displacement damage cross section is a generalization of nuclear cross section, current theories on the computation of self-shielded multigroup cross section are not directly applicable for the damage cross section.
Displacement damage cross section, briefly noted by Displacement per Atom (DPA) cross section hereinafter, is proportional to the product of nuclear reaction cross section and the average damage energy: σ_DPA (E)∝σ(E) E_a (E). There are three approaches to calculate the multigroup DPA cross section. Figure 1 shows the multigroup DPA cross sections computed with the three methods along with the quasi-point-wise (ECCO 1968 group) one for neutron elastic scattering on 56Fe. The first method is mathematically rigorous for computing multigroup cross section, but the self-shielding corrections on nuclear cross section cannot be directly applied. The latters can directly use the self-shielding corrections on nuclear cross section, whereas they are not mathematically well defined for multigroup reaction rate calculation.
The present work thoroughly studies the three approaches for computing multigroup DPA cross section and their influences on DPA rate based on Fe in the core and Mg in the reflector of a typical sodium-cooled fast breeder reactor. In addition, the uncertainty induced by the approximate treatments of self-shielded multigroup DPA cross sections is also quantified.