The Role of Temperature in the Safety Case for High-Level Radioactive Waste Disposal: A Comparison of Design Concepts

Joachim Heierli,Oliver Genoni

doi:10.3390/geosciences7020042

Abstract

The disposal of heat-generating radioactive waste in deep underground facilities requires a sparing use of spatial resources on the one side and favorable temperature conditions over the project lifetime on the other side. Under heat-sensitive conditions, these goals run in opposite directions and therefore a balance of some kind must be found. Often the elected strategy is to determine the size of the repository by capping the temperatures in the near-field, thus setting an upper limit to the deterioration of barrier materials. Alternatively, the spatial resources available in the siting area can be used to further reduce temperatures as long as supplementary benefits are returned from doing so. Using analytical modeling of the heat flow in the circumambient rock of a repository for high-level waste and spent fuel, this contribution examines possible obstacles in substantiating the safety case, namely the retrievability of waste during the operational lifetime of the facility, the representativeness of pilot disposal areas for monitoring, and the effect of thermal anomalies underground. The results indicate that there are, amongst the visited criteria, several benefits to the temperature-optimizing strategy over the prevailing space-optimizing concepts. The right balance between saving spatial resources and obtaining optimal temperature conditions is yet to be found.

Highlights

The disposal of heat-generating radioactive waste in deep underground facilities requires favorable temperature conditions over the project lifetime and beyond [1,2,3]
A practicable objective is to cluster the waste batches in order to save spatial resources
Between case A and case B, peak values differ by 30◦ C at P1 to almost 40 ◦ C at P2

Summary

Introduction

The disposal of heat-generating radioactive waste in deep underground facilities requires favorable temperature conditions over the project lifetime and beyond [1,2,3]. This category often includes further requirements such as retrievability of waste and pre-closure monitoring Current examples of this strategy are disposal concepts for heat-sensitive host rocks with low thermal conductivity (such as clays) and concepts making use of thermally degradable backfill materials (such as bentonite, a smectite-rich, clay-based buffer material interposed between the waste batch and host rock) [3]. In this situation, a viable strategy is to cap temperatures in the near-field so as to avoid detrimental effects to the barrier system [6].

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