Swelling Characteristics of a Type 304SS Baffle Plate Irradiated up to 50 DPA in PWR and Validation of a Swelling Equation

Abstract

When austenitic stainless steel is highly irradiated in a reactor under high temperature, voids will be created in the material, leading to volumetric expansion of structures. This phenomenon is known as void swelling. The deformation caused by the swelling possibly deteriorates the functionality of reactor internals in Pressurized Water Reactors (PWRs), especially baffle former assemblies. To evaluate the functionality of the internals against the swelling and to assure the structural integrity, simulation technologies play a key role, enabling the estimation of the swelling behavior of the internals through plant life. The simulation results strongly depend on inputs, especially on a swelling equation; however, it includes uncertainty to some extent because quite limited swelling data in PWR environment have been available, which are necessary for the validation of the equation. To enable the validation of swelling equations and improve the reliability on the simulations, the authors investigated the swelling characteristics of a type 304SS baffle plate removed from a decommissioned PWR plant. A total of nine swelling data were obtained with the variety in neutron dose (33 to 47 dpa) and irradiation temperature (299 to 327°C). The swelling ratios obtained are ranging from 0.02 to 0.08%, which corresponds well with the swelling equation, showing the similar temperature dependency with the equation. Since the irradiation temperature range of the obtained data, up to 327°C, covers major part of baffle former assemblies, swelling ratios of most part of them are expected to be small, which is probably too small to harm the functionality of the assemblies. The results contribute to the better confidence on swelling simulations and to assure the integrity of PWR reactor internals.