Long-term performance test of Cu canisters used for disposing of spent nuclear fuels under aerobic groundwater

Abstract

Evaluating the long-term corrosion behavior of Cu under local groundwater is important for its use in fabricating disposal canisters. The long-term performance of KJ-I bentonite-embedded Cu disks was assessed for a testing period of 10 years. The results were compared with those obtained on MX-80 bentonite-embedded Cu disks. The disks retrieved from the MX-80 and KJ-I bentonites exhibited corrosion depths of 0.53 and 3.9 μm, respectively. The corrosion rate below 0.39 μm/year indicated that Ca-type KJ-I bentonite can also be used as a buffer material. The surface characterizations revealed the formation of a thin Cu oxide layer (∼0.5 μm) on the MX-80 bentonite-retrieved disk. A Cu₂O layer (∼2 μm) was formed on the KJ-I bentonite-retrieved disk. During open-circuit potential measurements, the bentonite-embedded disk exhibited a potential below −125 mV, which is considerably lower than the pitting potential of Cu (∼250 mV), indicating that the occurrence of localized corrosion of Cu is largely reduced upon embedding in bentonite. This study demonstrates that KJ-I bentonite-embedded Cu canisters can be utilized for nuclear waste disposal under aerobic conditions.