Lead/lead-alloy as a corrosion-resistant outer layer packaging material for high level nuclear waste disposal

Abstract

Safe disposal of high-level nuclear waste (HLW) is a challenging problem world-wide. Corrosion-resistant waste packages constitute a key component of a multiple barrier system for waste isolation. Metallic copper has been proposed as an outer layer material for a waste package. However, a concern has been raised regarding potential copper corrosion induced by hydrogen sulfide in a reducing disposal environment. We here demonstrate that lead/lead-alloy materials could be an excellent alternative material for waste package outer layers, owing to their corrosion resistance (especially to hydrogen sulfide attack) and radiation-shielding capability. Our long-term (∼800 days) corrosion experiments show that lead could be passivated by a dense layer of sparingly soluble corrosion products, cerussite (PbCO3) and tarnowitzite (Ca,Pb)CO3, in contact with carbonate-bearing groundwaters. If needed, the carbonate concentration in a repository can be conditioned by adding carbonate materials such as calcite or hydromagnesite as a buffer material component to ensure cerussite precipitation. With its low solubility (<10–6 mol•kg−1), cerussite is more favored to form over galena (PbS) in a typical disposal environment. Thus, the issue of sulfide-induced metal corrosion as that happens to copper can potentially be eliminated. Furthermore, using lead/lead alloy will provide excellent radiation shielding for waste package transportation and repository operation.