Estimating the Lifetimes of Titanium Containers for Nuclear Fuel Waste: A DamageFunction for the Crevice Corrosion of Grade-2 Titanium (Estimation de la Duree de Vie des Conteneurs en Titane pour le Stockage des Dechets de Combustible Nucleaire: Fonction

摘要

The assumptions upon which the lifetime failure model used in the postclosureassessment is based are reevaluated. In particular, the conservatisms involved in assuming that crevice initiation would occur, and that sufficient oxygen would be present to maintain crevice propagation to failure, are discussed. Unless the period required to saturate the environment around the container can be specified with some certainty, it remains necessary to assume corrosion would initiate rapidly on all containers. A modified version of the container lifetime model has been developed which avoids the need to use averaged temperature profiles. In this model, these profiles are converted to propagation rate profiles using an experimental activation energy and then numerically integrated to predict container failure times. A damage function is developed relating the maximum depth of penetration by crevice corrosion to either the time since emplacement in the vault or the total amount of oxygen consumed. This function is used to estimate the maximum penetration depth expected if all the oxygen available in a borehole is consumed in crevice corrosion and to determine the impact on container lifetimes of various repassivation criteria. The factors likely to cause repassivation are summarzed, and a number of engineering approaches to extending container lifetimes suggested.