Assessment of neutron irradiation effects via PKA spectra, displacement damage, and gas production: Application to reactor pressure vessel

Abstract

Neutron irradiation damage is a major challenge for materials employed in radiation environments, such as Reactor Pressure Vessels (RPV). Based on a determined neutron flux, the present study assesses the neutron irradiation effects via Primary Knock-on Atoms (PKAs) production, the consequent displacement damage, and gas production. The complete PKA spectra including all minor isotopes from nuclear reactions are calculated and used to estimate the displacement damage and gas production. At the inner surface of the RPV, which suffers the strongest neutron irradiation, it is found that some minor PKAs have smaller atomic numbers and higher kinetic energies than dominant isotopes in RPV. These PKAs have much deeper ranges in RPV steel and may thus produce important damage other than point defects. The displacement damage is calculated using SRIM simulations and the corresponding corrections to ensure consistency with the NRT-dpa concept. Notably, the displacement damage in the RPV should be ∼23% higher than the prediction by the NRT-dpa formula, which cannot be directly applied to PKAs different from the target atom. The 4.1 H-appm/dpa and 0.2 He-appm/dpa gas productions at the RPV inner surface are higher than that in the innermost 1/4 thickness by a factor of 2 and 1.3, respectively.