Abstract
<p class="AMSmaintext">One concept for Czech canister construction for deep geological repository considers stainless steel as an inner case material. Corrosion resistance to localised (pitting/crevice) corrosion and stress corrosion cracking of austenitic stainless steel 316L and duplex steel 2205 was studied. The environment was synthetic bentonite pore water (SBPOW) of domestic bentonite BaM, or a slurry of bentonite in SBPOW. Tests were carried out between 40 °C and 90 °C under anaerobic conditions of a nitrogen atmosphere. The following methods were used for evaluation: potentiostatic tests at oxidation-reduction potential of the environment, long-term exposure tests in SBPOW and slurry, slow strain rate tensile test (SSRT), exposure test of U-bends, and optical microscopy. Results showed no susceptibility of either material to stress corrosion cracking. No localised corrosion was observed up to 70 °C. There was no localised attack observed in SBPOW at 90 °C, but there was localised corrosion detected in the bentonite slurry. Forced breakdown of the passive layer during SSRT, and artificial crevices (O-rings), showed no effect on localised corrosion propagation. The detrimental effect was probably a result of the adsorption ability of the bentonite particles, which allowed breakdown of passive layer and disabled repassivation of metastable pits.</p>
Highlights
The Czech concept [1,2,3,4,5,6,7,8] of a HLW canister for deep geological repository considers three combinations of metallic material inner/outer case: stainless steel/carbon steel, carbon steel/copper, carbon steel/TiPd alloy
The aim of this study is to verify the possibilities of crevice/pitting corrosion and stress corrosion cracking in anaerobic bentonite pore solution and bentonite slurry
Neither mass loss were estimated nor the localised attack was observed visually up to 70 °C in bentonite slurry even when contaminated by iron corrosion products, which could be in real conditions form carbon steel outer case
Summary
The Czech concept [1,2,3,4,5,6,7,8] of a HLW canister for deep geological repository considers three combinations of metallic material inner/outer case:• stainless steel/carbon steel, • carbon steel/copper, • carbon steel/TiPd alloy. In the first concept, a uniformly (predictable) corroding carbon steel case should overcome at least the aerobic period, when crevice corrosion would arise for sure on stainless steels. This work should verify what conditions in a repository could be acceptable for stainless steel. All oxygen is supposed to be consumed relatively fast in the repository, but the temperature could still be high, at 90 °C. The final temperature of the repository will be close to that of the host granitic rock. A conservative value is 40 °C, but the real temperature will probably be lower. According to the mechanism of crevice corrosion, this kind of attack, based on differential aeration inside and outside the crevice is not very probable under anaerobic conditions. Pang and DOI 10.12776/ams.v25i1.1197 p-ISSN 1335-1532 e-ISSN 1338-1156
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