Search

The advanced technologies of modern civilization produce radioactive wastes that require careful disposal if they cannot be recycled. These materials can originate from a variety of activities, such as scientific research, medicine, or nuclear power generation and, as such, can result in numerous waste forms. In this paper, the corrosion behavior of several less‐common metals is studied, specifically: aluminum, copper, lead, magnesium, zinc, and zirconium, all under simulated cementitious environments. The data reported rely on the production of hydrogen as a corrosion end‐product to calculate the uniform corrosion rate as a function of time. At 50°C, in either young cement water (pH 13.5) or saturated portlandite (pH 12.5) and after approximately 2 years of exposure, magnesium was found to corrode at ∼10 µm/year; aluminum at 1 µm/year (portlandite only); zinc at ∼100 nm/year; lead at <1 nm/year and both copper and zirconium at less than 0.1 nm/year. [ABSTRACT FROM AUTHOR]

The long‐term disposal of nuclear waste in deep geological repositories requires safe containment for up to one million years. To understand how the waste will respond to the gradually evolving environment, researchers can perform sensitive experiments in the laboratory to replicate the repository conditions at specific time points. In Belgium, spent nuclear fuel will be housed within a carbon steel overpack, which is encased within a cement buffer, which may include a stainless steel liner (the "envelope"). The range of corrosion behaviors for carbon steel, and to a lesser extent, stainless steel, has been studied through hydrogen evolution, an end‐product of oxidation under repository conditions. Considerable time may be required for metallic surfaces to approach a steady hydrogen evolution and this is dependent upon the starting condition of the specimen surfaces. The use of nominally‐similar materials can result in significant variation in the reported corrosion rates. The presence of cements, which generate their own hydrogen and influence water chemistry as a function of time, add complexity to even simple experimental configurations that requires careful interpretation. [ABSTRACT FROM AUTHOR]

Copper has been proposed as a corrosion barrier for used fuel containers due to its thermodynamic stability under the anoxic conditions relevant to a deep geological repository. Laboratory simulations of anticipated repository conditions have demonstrated the production of small quantities of hydrogen gas, which have been interpreted as being indicative of an oxidation (corrosion) process. This work reports new corrosion results for repository‐relevant materials: electrodeposited copper, cold spray copper and junction material under Canadian and Swiss simulated ground waters. The attribution of the recorded hydrogen suggests corrosion is limited to the outermost atomic layers of copper cladding. However, the origins of the hydrogen have not been conclusively determined. Three thermal desorption methods have been used to investigate the outgassing of hydrogen from electrodeposited copper which may permit a more accurate interpretation of the hydrogen evolution profile from corrosion cells. [ABSTRACT FROM AUTHOR]

The long‐term disposal of low‐ and intermediate‐level radioactive waste is anticipated to involve the encapsulation of the material within a cementitious matrix before placement in a deep geological repository. After sealing, the waste repository will become anoxic and the corrosion of emplaced metals will result in the production of hydrogen gas. Knowledge of the rate at which this hydrogen is generated is valuable in that it permits the assessment of pressure build‐up within the repository. The corrosion behavior of mild steel has been monitored through the generation of hydrogen gas, under simulated repository conditions that mimic various stages of cement evolution. It was found that, when cement is used to encapsulate steel, the passage of several years is required for the steel and cement to reach a steady hydrogen production rate. Steel that is directly immersed in simulated cement pore water requires only months to stabilize. All measured steel uniform corrosion rates were significantly below 1 nm year−1 at 50°C, regardless of the test environment, after more than 4 years of exposure. [ABSTRACT FROM AUTHOR]

In this paper, carbon steel corrosion rates from experiments performed in situ (performed in an underground rock laboratory) and ex situ (performed in a conventional laboratory) test methods in anaerobic saturated bentonite are compared. The results indicate that the long‐term corrosion rate follows a power law decay curve, with a higher initial rate and greater rate of decay at higher temperature. In compacted bentonite blocks, varying the density has no significant effect on the corrosion rate measured during in situ testing, whereas granular bentonite of an equal dry density leads to a higher corrosion rate. Precorrosion of test specimens in an aerated solution at room temperature has a negligible effect on the subsequent anaerobic corrosion rate when tested ex situ for durations up to 11.8 years. The main difference between in situ and ex situ tests is the formation of silicon‐rich corrosion products in the ex situ tests but not in the in situ tests. Despite these differences, the corrosion rates in both tests exhibit the same general temporal evolution and similar magnitudes, suggesting that the main steel degradation processes are maintained in both configurations. [ABSTRACT FROM AUTHOR]

Microscopic and spectroscopic analyses were conducted on steel/bentonite interface samples removed from four in situ experiments that were carried out in three underground research laboratories at different temperatures and under different hydraulic and geochemical conditions. The results provide valuable information about the corrosion processes occurring in high‐level radioactive waste repositories. Systematic patterns can be deduced from the results, irrespective of carbon steel grade, type of bentonite and its degree of compaction, geochemical environment or experimental setup. Thus, a clear dependence of the corrosion rates on temperature and exposure period, as well as on the availability of H2O and O2 provided by the surrounding bentonite buffer, is observed. Furthermore, Fe(II) ions released by corrosion interact with the structural Fe in the clay. Recent developments highlight the usefulness of reactive transport modelling in understanding the coupled corrosion and Fe–clay interaction processes. [ABSTRACT FROM AUTHOR]

Since 2012, a long‐term in situ corrosion experiment (IC‐A) is being conducted in the Mont Terri Underground Research Laboratory in Switzerland to investigate the corrosion behaviour of candidate canister materials in conditions representative of the Swiss concept for the disposal of high‐level waste and spent nuclear fuel. To date, carbon steel and various types of copper coatings have been retrieved after different exposure periods of up to 3 years, and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, the nature of the interaction between the metal and the surrounding bentonite, and the microbial populations in the bentonite and surrounding porewater. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Much less alteration on either the metal or the bentonite was observed in the case of copper samples. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials. This paper summarises the results of the experimental programme obtained to date and discusses the relationship observed between exposure time and the evolution of the metal–bentonite interface for both carbon steel and copper. [ABSTRACT FROM AUTHOR]

The Swiss waste management programme foresees that low‐ and intermediate‐level radioactive waste will be disposed of in a deep geological repository constructed in Opalinus Clay. Gas generation is expected in the repository due to the decomposition of organic materials and the corrosion of metals, with carbon steel being the primary source. The corrosion behaviour of mild steel under anoxic conditions has been studied over the course of several years to better understand the long‐term hydrogen evolution profile under anticipated repository conditions. Steel, either bare or encased within mortar, was tested in water vapour or immersed in electrolytes representative of aged cement waters at 50°C. The corrosion rate was measured indirectly through the hydrogen analysis using a solid‐state probe. The hydrogen evolution behaviour of grout was also monitored to more accurately determine the hydrogen generating from the corrosion of the embedded steel. For steel in water vapour or in alkaline environments, embedded in cementitious material or immersed in simulated aged cement pore water, corrosion rates were invariably <1 nm/year after several years of analysis. [ABSTRACT FROM AUTHOR]

The materials corrosion test (MaCoTe) is a long‐term, multinational in situ corrosion experiment setup at the Grimsel Test Site, Switzerland. The experiment has been operating since 2014 with a focus on the corrosion behaviour of container materials for the disposal of high‐level waste and spent nuclear fuel under conditions representing a granitic deep geological repository. The experiment consists of eight modules containing metal coupons and bentonite. Two of the modules, each with a different bentonite density, have been retrieved after 394 days of exposure and have been analysed using a range of techniques aimed at studying the corrosion behaviour of the metals and the mineralogical evolution of the bentonite. Weight loss measurements show that carbon steel had a relatively low average corrosion rate (~2 µm year−1). Much lower average corrosion rates were measured for the various types of copper (0.13–0.32 µm year−1). No detectable corrosion was measured on stainless steel coupons. To date, no significant differences were observed in the corrosion behaviour and rate of the test metals in bentonite with different dry densities. [ABSTRACT FROM AUTHOR]

Deep geological repositories for radioactive waste contain metallic materials, either used to construct disposal canisters or as low‐/intermediate‐level waste (L/ILW). The safety relevance of corrosion is linked to canister lifetime in the former case and gas generation in the latter. More specifically, the Belgian "supercontainer" concept envisages mild steel for the used fuel disposal canister, and in the case of the Swiss L/ILW repository, mild steels are the largest metallic waste component due to the decommissioning of civilian power‐generating facilities. For these circumstances, the corrosion environment is dominated by the chemistry of cement, which is used as buffer or backfill material. The corrosion behaviour of mild steel in anoxic environments was studied through the analysis of the hydrogen end‐product. Hydrogen analysis was conducted by periodically purging the cell head‐space and analysing the gas using a solid‐state hydrogen sensor. While this method is limited to providing only uniform corrosion rates averaged over periods of time, ranging from weeks to months, it provides excellent resolution and sensitivity. The test cell environments were matched against the anticipated Belgian high‐level waste and Swiss L/ILW repository environments, and also against experiments that have been conducted by other researchers for comparative purposes. Samples were exposed to synthetic cement pore waters, representing fresh and degraded cement. In young cement waters, the formation of initial corrosion products resulted in steel wire corrosion rates of the order of µm/year, which, at 80°C rapidly declined to ∼10 nm/year. In contrast, SA516 grade 70 steel plate corroded much more slowly under similar conditions. In aged cement waters, initial corrosion rates were higher but declined faster towards a longer‐term rate of ∼10 nm/year. 316L stainless steel, embedded in cementitious material, corroded at a rate of <1 nm/year at 50°C. [ABSTRACT FROM AUTHOR]