Quantitative evaluation of the geochemical / microbiological processes within extended storage repositories

Radioactive waste repositories are generally designed to be 'simple' facilities with the main aim of emplacing the waste and closing the facility in a short time period. However, some recent repository designs for cavern emplacement combine many of the advantages of the flexibility provided by long-term interim storage with the safety of deep geological disposal. Over long periods when the waste is under a storage regime, there may be considerable biogeochemical alteration of engineered structures and the surrounding rock. Such processes could influence both the integrity of structural components and the subsequent long-term performance of the sealed repository. Scoping calculations indicate that the properties of the tunnel liner play a critical role in determining the practicality of this option. Further concerns with such concepts are associated with the practicality of early closure should this be required and hence this is also discussed. (author)