Development of Sealing Materials for Application in Engineered Barriers of a Conceptual Deep Geologic Repository for Used Nuclear Fuel: Filling the Gaps

Abstract

Concepts for the deep geologic disposal of used CANDU fuel generally have most of the excavated emplacement-room volume filled with the waste-package and pre-manufactured sealing system components (e.g. highly compacted bentonite, bentonite-sand buffer, densely compacted backfill). In addition to these components, gaps are present between the various components and between the components and the rock perimeter that need filling. Materials to fill these gaps are generally referred to as gap fill (GF) or light backfill (LBF) and they play an important role in ensuring that the entire sealing system performs as intended. GF and LBF materials are particularly important in ensuring that the used fuel container is protected from adverse effects such as excessive displacement of the surrounding sealing materials and microbially-influenced corrosion. Maximizing the density and minimizing the water activity (aw) of the materials placed within these gaps are important in ensuring that adjacent materials maintain their ‘as-placed' condition as closely as possible and that areas immediately adjacent to the containers do not become conducive to microbial activity. In this paper, potential GF and LBF materials are investigated and their potential effects on the activity of the microbial population within the sealing system are described.