Review of the Modelling of Corrosion Processes and Lifetime Prediction for HLW/SF Containers—Part 1: Process Models

Abstract

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since HLW/SF containers are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of long-term corrosion behaviour, including models for uniform and localised corrosion, environmentally assisted cracking, microbiologically influenced corrosion, and radiation-induced corrosion. More recently, fracture-mechanics-based approaches have been developed to account for joint mechanical–corrosion degradation modes. Regardless of whether empirical or deterministic models are used, it is essential to be able to demonstrate a thorough mechanistic understanding of the corrosion processes involved. In addition to process models focused on specific corrosion mechanisms, there is also a need for performance-assessment models as part of the overall demonstration of the safety of a deep geological repository. Performance-assessment models are discussed in Part 2 of this review.

Review of the Modelling of Corrosion Processes and Lifetime Prediction for HLW/SF Containers—Part 2: Performance Assessment Models

“…The nature of the disposal environment is described in some detail in Part 1 [1], along with a discussion of the implications for the long-term corrosion performance of the container. One of the most important aspects of the repository environment is that it evolves over time.…”

“…Table 2. Corrosion processes for reference container materials in various national nuclear waste programs [1].…”

“…Table 4 provides an overview of the different approaches used for the prediction of the long-term corrosion performance in PA models for the four broad classes of container material. As can be seen, there is a general reliance on empirical corrosion rates or damage functions (i.e., pitting factors, surface roughness allowances and statistical analysis of observed pit depths), rather than the use of deterministic approaches favoured for the development of process models [1]. Deterministic models are, however, used for developing reasoned arguments for excluding various corrosion processes.…”

“…Many different types of predictive model have been developed for this purpose over the past 45 years and which are the subject of this review. For convenience, the review has been divided into two parts, with process models focussed on specific corrosion processes or mechanisms discussed in Part 1 [1] and performance assessment models for the prediction of container lifetimes described here in Part 2. In addition to a discussion of process models, Part 1 also contains much information regarding the nature of the disposal environment and how it evolves over time, which should be reviewed as background to the discussion of performance assessment models described here.…”

“…Radiation-induced corrosion (RIC)-different process models have been used to assess the extent of RIC [1]. Generally, these assessments have involved uncoupled radiolysis models in which a bulk radiolysis model is used to predict the amounts of radiolytic oxidants that could be formed, and a separate corrosion model is used to predict the extent of damage.…”