Attenuation of neutron and photon-induced irradiation damage in pressurized water reactor pressure vessels

Abstract

The present work investigates the attenuation of neutron and photon-induced irradiation damage in a Pressurized Water Reactor (PWR)-like mock-up Reactor Pressure Vessel (RPV) using Tripoli-4® Monte Carlo simulations with a particular emphasis on the presence of a thick stainless steel heavy reflector between the core and RPV. Results show that the photon-induced damage is well described by the exponential law. The neutron-induced damage attenuates quicker than the exponential form near the outer surface of RPV. Nevertheless, an exponential form can represent the attenuation of neutron-induced damage within 5% discrepancy for penetration < 17 cm in a typical 22 cm thick RPV and within 20% in the outermost 3 cm. The exponential form with an additional negative term fits the attenuation of neutron-induced damage in RPV as the negative term considers the “leakage” of neutron near the outer surface. It is observed that the presence of a Gen III-like representative heavy reflector reduces the estimated neutron-induced damage by a factor of 2. On the other hand, this paper verifies that the neutron flux with energies above 0.5 MeV (ϕ>0.5) is more representative of the displacement damage attenuation than the flux above 0, 0.1, and 1 MeV in RPVs. The damage rate is approximatively equal to Kϕ>0.5 with K=9.5×10-22DPA/n∙cm-2 in PWR RPVs.