Calculation of Displacements Per Atom (DPA) in the Reactor Vessel of VVER-1200 Using arc–DPA Methodology

Neutron irradiation damage is one of the most critical degradation mechanisms in reactor pressure vessel (RPV) steel. Traditional displacement damage models, such as NRT-DPA, tend to overestimate stable defect production by neglecting athermal recombination effects. However, the generated vacancies undergo athermal relaxation, leading to a reduction in the stable number of vacancies. This study focuses on incorporating athermal relaxation effects into the final vacancy distribution, building on the results of the previous work (Khrushchinsky et al., 2024) where the distribution was obtained without considering athermal relaxation. The calculations are performed for the VVER-1200 reactor pressure vessel using the arc–DPA (displacements per atom with athermal relaxation correction model), providing a more accurate assessment of radiation-induced damage. Additionally, we estimate the annual arc-vacancy accumulation, providing improved lifetime assessments for the VVER-1200 RPV. This work highlights the importance of advanced damage models for accurate safety evaluations in nuclear reactors.