Study on the self-shielding and temperature influences on the neutron irradiation damage calculations in reactors

摘要

Displacement per Atom (DPA) is conventionally computed using the DPA cross sections in reactor applications. The DPA cross sections can be influenced by temperature through the Primary Knocked-on Atom (PKA) energy and the Doppler broadening of reaction cross sections. The former is shown not important due to the threshold energy of atomic displacement and the small value of thermal kinetic energy. For Fe-56, the Doppler broadening has limited influence on DPA cross sections due to high resonance energies. On the other hand, the self-shielding should be considered in the computation of DPA, which depends not only on the cross sections but also the corresponding recoil energies of the PKA. ECCO 1968-group calculations show that the self-shielding corrections on DPA cross sections are necessary for the computation of atomic displacement. In addition, the total DPA rate calculated by self-shielding corrected total cross sections is smaller than the sum of partial components. The recommended method to compute DPA is the calculation of each reaction, especially for coarse energy structures. The total DPA rate in ASTRID reactor inner core is 25 DPA/year, for which the contributions of the elastic scattering, total inelastic scattering, and disappearance reactions are 81.9%, 18.0%, and 0.1%, respectively. The corresponding relative reductions due to the corrections of multi-group cross sections are 11.3%, 5.9%, and 20.5%, respectively.