Long-Term Isolation of High-Level Radioactive Waste in Salt Repositories Containing Brine

Abstract

At present, only one concept, the Swedish design utilizing a thick-walled copper waste package, has been accepted as being capable of isolating high-level waste for hundreds of thousands of years in a granite-type repository.Theoretical arguments show that after the relatively short times required for salt consolidation selfshielded thin-walled copper waste packages have no significant failure or degradation reactions in anoxic neutral and acid brines.Thermodynamic analyses of reactions after consolidation (constant-volume reactions under lithostatic pressures in the absence of oxygen) show that miniscule amounts of metal reacting with brine can produce very large hydrogen pressures. For copper waste packages, almost no consumption of copper is required to produce the small equilibrium hydrogen pressure needed to prevent reaction. Reaction under these conditions no longer depends on poorly understood corrosion mechanisms, but results from hypothetical mechanisms that allow the equilibrium hydrogen to migrate away from the waste package.Analyses of gamma radiolysis and diffusion processes show that in an array of thousands of waste packages removal of hydrogen from the outer packages should be negligible for a properly selected salt repository.