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51318-11707-Corrosion of steel in high-level radioactive waste rock repositories: kinetics and thermodynamics

The corrosion of stainless steel AISI 309S, one of the recommended materials, was investigated in a representative salt brine by a special designed high-pressure and high-temperature electrochemical reactor.

Product Number: 51318-11707-SG
Author: Andrés G. Muñoz / Dieter Schild
Publication Date: 2018
Industry: Energy Generation
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The corrosion of stainless steel containers for the disposal of radioactive spent fuels can be triggered, provided it comes into contact with waters of high salinity in geological formations. Apart from its extremely aggressive environment, the repository is characterized by high hydrostatic and ground pressures (p > 100 bar). Also, temperatures of 100-150°C can be reached due to the release of fission heat during the first 150 years of disposal. The corrosion of stainless steel AISI 309S, one of the recommended materials, was investigated in a representative salt brine by a special designed high-pressure and high-temperature electrochemical reactor. Under the extreme repository conditions, stainless steel may be susceptible to pitting corrosion. Morphological analysis of the attacked surface performed by SEM-EDX show that pits grow both laterally and downwards in vertically arranged samples. The chemical analysis of the pit surface by XPS reveals the formation of a chromium enriched oxide. The thermodynamic modelling of the corrosion process using the Geochemist´s Workbench® tool predicts a strong acidification of the pit environment during its initial growth induced by dissolution of chromium. Chromium and nickel oxides are precipitated during repassivation. This provides further arguments for explaining the particular pit growth mechanism.

Key words: stainless steel corrosion, salt rock, thermodynamic modelling, Pitzer formalism.

The corrosion of stainless steel containers for the disposal of radioactive spent fuels can be triggered, provided it comes into contact with waters of high salinity in geological formations. Apart from its extremely aggressive environment, the repository is characterized by high hydrostatic and ground pressures (p > 100 bar). Also, temperatures of 100-150°C can be reached due to the release of fission heat during the first 150 years of disposal. The corrosion of stainless steel AISI 309S, one of the recommended materials, was investigated in a representative salt brine by a special designed high-pressure and high-temperature electrochemical reactor. Under the extreme repository conditions, stainless steel may be susceptible to pitting corrosion. Morphological analysis of the attacked surface performed by SEM-EDX show that pits grow both laterally and downwards in vertically arranged samples. The chemical analysis of the pit surface by XPS reveals the formation of a chromium enriched oxide. The thermodynamic modelling of the corrosion process using the Geochemist´s Workbench® tool predicts a strong acidification of the pit environment during its initial growth induced by dissolution of chromium. Chromium and nickel oxides are precipitated during repassivation. This provides further arguments for explaining the particular pit growth mechanism.

Key words: stainless steel corrosion, salt rock, thermodynamic modelling, Pitzer formalism.

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