Incorporation of “Corrosion-Time” and Effects of Corrosion-Product Spalling in Waste Package Degradation Simulation in the Potential Repository at Yucca Mountain

Abstract

ABSTRACTA two-layer waste package (carbon steel outer barrier and Alloy 825 inner barrier) is specified to dispose of high-level nuclear waste at the potential repository at Yucca Mountain. A set of improvements and more realism have been added to a stochastic waste-package degradation model which was developed for a recent total system performance assessment of the potential repository [1]. The waste-package surface is divided into “patches” to better represent the general corrosion of the carbon-steel outer barrier. The “corrosion-time” concept is developed to represent the corrosion of the carbon-steel outer barrier in changing exposure conditions with time such as those expected in the potential repository. With the patches approach and the corrosion-time concept implemented into the waste-package degradation model, sensitivity of the waste package degradation (failure and pitting degradation) to different threshold spalling thicknesses of the corrosion products from the carbon-steel outer barrier is analyzed. The results show that the waste-package pitting degradation is sensitive to the corrosion-products spalling thickness of the carbon-steel outer barrier. A greater pitting degradation of the waste packages is predicted with a smaller spalling thickness. Further understanding of the corrosion-products spalling in different exposure conditions (i.e., water chemistry, water contact mode, etc.) and its effects on carbon steel corrosion is needed to enhance the confidence in the waste-package performance modeling in the potential repository.