Investigating the effect of bentonite compaction density and environmental conditions on the corrosion of copper materials

Abstract

The proposed long‐term management plan for used nuclear fuel is to isolate it within a multiple‐barrier system underground in a deep geological repository (DGR). In the Canadian design, used fuel bundles will be sealed in copper‐coated carbon steel used fuel containers, encased in blocks of bentonite clay, emplaced approximately 500–800 m below ground, and surrounded by a bentonite gapfill material. A laboratory experimental campaign has been undertaken to demonstrate the integrity of the multiple‐barrier system. DGR‐relevant copper materials were embedded in bentonite clay, compacted to various densities, and sealed into a hermetic pressure vessel pressurized with demineralized water. Experiments explored the influence of bentonite compaction in the range of 1100–1600 kg/m3 on copper corrosion over durations of 1–18 months. Postexposure analysis of the copper coupons showed nonhomogeneous corrosion, with corrosion products composed of Cu2O, with some Cu2S. The average corrosion rates decreased as a function of time and increasing bentonite compaction density. In general, we observed that higher bentonite compaction density suppressed the corrosion of embedded copper.