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

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/m(3) 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.