Investigation of the fretting wear performance of accident tolerant cladding options for light water reactors

Abstract

A leading cause of fuel failures in U.S. pressurized water reactor power plants is grid-to-rod fretting. Kanthal advanced powder metallurgy technology or APMT, an FeCrAl steel alloy, and a braided SiC fiber, Chemical Vapor Infiltration SiC matrix (SiC/SiC) cladding by General Atomics are investigated as alternatives to conventional fuel cladding in a nuclear reactor due to their favorable performance under accident conditions. Tests were performed to compare the reliability of the cladding candidates and a conventional cladding, Zircaloy-4, under dry fretting conditions at elevated temperature. Wear coefficient measurements showed that APMT steel performs favorably in comparison to Zircaloy-4 with respect to fretting wear. The coefficient of friction evolution with temperature was investigated for APMT steel. COF measurements showed APMT steel's COF and wear decreases with temperature up to 350C due to the growth of a protective alumina and chromia oxide layer. Nanofretting wear of the cladding materials was investigated. A model was developed to calculate the wear coefficient from the spherical indenter tip depth and was in agreement with the wear coefficient calculated from 3D confocal microscopy wear volume. The results were compared to the conventional fretting wear tests for the same materials and determined that they were in agreement for their relative wear performance. Archard's wear equation is supported with nanofretting wear coefficient values for the metallic materials with respect to their change in hardness.