Abstract
This study explores the corrosion interactions between a metallic canister material, stainless steel (SS) 316, and an I-bearing ceramic waste form, lead vanado-iodoapatite (I-APT, Pb9.85(VO4)6I1.7), in a chloride solution. Crevice corrosion of the SS in close proximity to the I-APT resulted in the development of an aggressive environment at the interface of the two materials, which was acidic and enriched in Cl− anions. I-APT also corroded in the crevice region, primarily through ion-exchange between the I− ions from the I-APT matrix and anions from the environment. The enrichment of Cl− anions within the occluded crevice space as the result of SS crevice corrosion enhanced the corrosion of I-APT. The release of iodine from this apatite waste form could be accelerated owing to this mechanism. This is evidenced by a depletion of iodine from the I-APT matrix and a large amount of Cl-bearing precipitates on the surfaces of both SS and I-APT. On the other hand, the corrosion of I-APT leads to the precipitation of a V- and Pb-rich layer, which inhibits the localized corrosion of SS to an extent. This study advances the understanding of the near-field corrosion interactions between metallic canisters and ceramic waste forms.
Highlights
The immobilization of iodine-129, one of the problematic fission products, has been a major challenge for high level waste (HLW) disposal because of its high toxicity and volatility, as well as its extremely long half-life[1]
To simulate the near field corrosion interactions between stainless steel (SS) metallic canisters and encapsulated ceramic nuclear waste forms, SS was corroded in close proximity to I-APT in 0.6 M NaCl solution at 90 °C
A large amount of precipitates is visible near the boundary of the SS/ I-APT contact area
Summary
The immobilization of iodine-129, one of the problematic fission products, has been a major challenge for high level waste (HLW) disposal because of its high toxicity and volatility, as well as its extremely long half-life[1]. Synergistic interactions were found between the SS crevice corrosion and the corrosion of Cr-bearing hollandite ceramic waste forms The corrosion of both materials released cations such as Cr3+ that could accumulate within the confined crevice space between the SS and hollandite. When designing new waste forms, their potential corrosion interactions with metallic canisters should be considered. When SS is corroded in close proximity to I-APT, apart from the enhanced local acidity, the enrichment of Cl− at the material interface could accelerate the release of I− ions from I-APT With this hypothesis, the two materials were pressed against each other and corroded in 0.6 M NaCl solutions at 90 °C for a period of 28 days. Mo implications of this study to anoxic environments are provided in appears to be enriched, indicating the incorporation of corroded
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