Evaluation of Iron-Base Materials for Waste Package Containers in a Salt Repository

Abstract

Design studies for high-level nuclear waste packages for salt repositories have identified low-carbon steel as a candidate material for containers. Among the requirements are strength, corrosion resistance, and fabricability. The studies of the corrosion resistance and structural stability of iron-base materials (particularly lowcarbon steel) are treated in this paper. The materials have been exposed in brines that are characteristic of the potential sites for salt repositories. The effects of temperature, radiation level, oxygen level and other parameters are under investigation. The initial development of corrosion models for these environments is presented with discussion of the key mechanisms under consideration.

The Analytical Repository Source-Term (AREST) model: Description and documentation

“…More relevant tests of groundwater-plus-barrier materials, however, indicate that the presence of reactive solids typically suppresses reactions observed in tests only involving groundwater. Corrosion tests conducted under conservatively high gamma irrajiation (McCright, Van Konynenburg, and Ballou 1984;Westerman et al 1984) ha>'e confirmed measurable increases in corrosion rates, generally by factors of 2 to 5, attributable to radiolytic production of oxidizing species. Studies of the reaction of radioactive waste forms with groundwater have shown measurable changes in dissolution rate (Bibler, Wicks, and Oversby 1985) and solubility (Rai and Ryan 1984) attributable to the generation of radiolytic species.…”

“…Several predictive models of the rate of uniform corrosion, in addition -T:.O the generalized mechanistic model described in Appendix A, have been programmed for use in AREST. These include the Basalt Waste Isolation Project (BWIP) model of uniform corrosion of the waste package container (Anantatmula, Delegard, and Fish 1984) and a model of uniform corrosion developed for the Salt Repository Project (SRP) (Westerman et al 1984…”

“…The BWIP model also requires several additional empirically derived input values that depend upon environmental conditions. Inputs to the SRP model (Westerman et al 1984} include temperature, the area of the exposed surface, and the irradiation rate of the container material. Coefficients are fitted using experimental data.…”

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

“…Although one might think that it would be possible to make long-term predictions based on an empirical relationship between the corrosion rate and dose rate, there have been few such models published. Westerman et al [199] developed a semi-empirical model based on fitting experimental corrosion rates to a conceptual model for the competing production and consumption reactions for radiolytic species. In addition, Marsh and Taylor [5] describe the estimation of an effective G-value for the yield of radiolytic oxidants based on the degree of enhancement of the rate of uniform corrosion of carbon steel (By convention, the notation g-value is used here to refer to the yield of primary radiolysis products and the term G-value is used to refer to the net yield of a species based on both primary interactions and secondary reactions.…”

“…Radiolysis effect on iron-base materials Empirical Semi-empirical model based on fitting experimental corrosion rates to conceptual model for competing production and consumption reactions for radiolytic species. [199] Effective G-value Empirical The overall yield of radiolytic oxidants (the effective G-value) was calculated from empirical data based on the enhancement of the rate of corrosion in the presence of radiation. The effective radiolytic yield was then used as an input to a reactive transport, mixed-potential model.…”