The long-term performance of the Canadian deep geologic repository (DGR) relies significantly on bentonite clay, as sealing materials intended for use in the engineered barrier system (EBS). One particular safety concern is microbiologically influenced corrosion of the used fuel containers (UFCs) which may occur if bisulfide (HS-) transports through the bentonite buffer to reach the UFC surface and corrode the copper coating. Understanding HS- sorption onto bentonite is therefore an important aspect of this problem, as HS- sorption can reduce the extent of copper corrosion. However, sorption dynamics onto bentonite are not yet well-understood. As such, this study performed laboratory batch experiments to investigate HS- sorption onto bentonite slurries as a function of temperature (10-40 °C), pH (9-11), and ionic strength (0.01 M-1 M NaCl). These conditions were aimed to reflect the range of possible DGR geochemical conditions. The experimental results showed that HS- sorption onto bentonite increased with increasing temperature but decreased with increasing pH and ionic strength. A 3-way ANOVA (analysis of variance) showed that the variables' individual and 2-way interaction effects are statistically significant, which implies that they should be incorporated into a sorption mechanism. A thermodynamic-based sorption model was also developed in PHREEQC assuming that sorption was driven by three key processes: (i) redox reaction with the structural Fe3+ sites, (ii) surface precipitation as FeS (mackinawite), and (iii) surface complexation reactions with surface hydroxyl group (OH) at the edge sites of montmorillonite. The model successfully described the main experimental trends and provided valuable insights into the relative contribution of these processes to the total HS- sorption mechanism. Altogether, this study provides novel insights from experimental and numerical modelling findings that enhance the understanding of HS- sorption onto bentonite, in the context of Canadian DGR design as well as other nuclear repositories worldwide.

ABSTRACT The multi-national in situ Materials Corrosion Test (MaCoTe), being conducted at the Grimsel Test Site in Switzerland, assesses the stability of bentonite as it may be utilized within deep geological repositories (DGRs), which are proposed for the safe, long-term disposal of used nuclear fuel. This experiment provides an opportunity for long-term assessments of changes in microbial communities associated with compacted subsurface bentonite samples exposed to a natural groundwater. Leveraging samples from MaCoTe, herein, we report temporal data for the abundance and community composition of microorganisms associated with compacted bentonite samples emplaced over 7 years under in situ subsurface conditions. Phospholipid fatty acid analysis, 16S rRNA gene quantification and sequencing, cultivation, and natural organic matter analyses all indicated no significant changes for microbial community abundances associated with inner layers of bentonite samples over the 7 years. While microbial abundances did not change in the inner layers, the PLFA data suggest potential changes in microbial community composition and could also indicate prolonged microbial turnover rates. Overall, the results support microbial stability in compacted bentonite exposed to DGR-like conditions for at least 7 years. IMPORTANCE Long-term assessments of changes in microbial activity in compacted low-biomass bentonite systems analogous to deep geological repositories (DGRs) are critical to test conditions for stable engineered bentonite barrier components. This study assesses long-term temporal changes in microbial communities of compacted bentonites exposed to natural groundwater. It offers 7-year data that indicate stability of bentonite-based materials intended for use in engineered barrier systems of a DGR for the safe, long-term disposal of used nuclear fuel, with wider implications for microbial persistence in a deep subsurface environment.

Hydrogen gas (H2) generation due to microbially influenced corrosion (MIC) is an important evaluation to build confidence in long term safety of the Canada’s proposed high level nuclear waste deep geological repository (DGR). Numerical modelling can be a powerful tool as the DGR design life far exceeds the timescales of laboratory or field studies. This work presents the first numerical modelling study exploring long-term H2 dynamics under DGR environments. The key processes relevant to H2 production and consumption are identified and two numerical models are presented; one that focuses on H2 transport through the bentonite buffer and host rock, and another that considers production of H2 through MIC and the biotic H2 consumption (modelled through a simplified approach). This work is to investigate whether the net amount of H2 would surpass the solubility limit leading to H2 gas formation, using conservative assumptions of HS− and H2 flux conversion when sulfate is a non-limiting species. The modelling study showed that long-term H2 production from MIC may depend on HS− supply to the UFC, H2 transport properties, and biotic H2 consumption processes. While the HS− supply could increase the H2 formation, H2 transport through the rock and biotic H2 consumption processes were shown to control the accumulation of H2. Amongst various modelling scenarios, the H2 solubility limit was never surpassed, indicating the unlikelihood of H2 gas pressure build-up in a DGR under these modelling conditions. Altogether, this study provides valuable insight into H2 production, consumption, and transport dynamics in a DGR environment.

The effect of chloride on the corrosion mechanism of copper in deaerated, 0.1 M HNO3 was studied by electrochemistry, atomic force microscopy, and scanning electron microscopy. Nitrate reduction, the first cathodic step in the corrosion pathway, was completely inhibited in the presence of ppm levels of chloride, thereby shutting down the corrosion sequence of the system involving solution reactions by copper ions and the subsequent reduction of NO2-. Nitrite reduction was minimally affected, suggesting that the two reduction steps differ substantially in their sensitivity to the surface state during corrosion. Our results support the proposal that the key step responsible for the inhibitive effect of chloride is the adsorption of chloride to form an adlayer on the surface. Nitrate reduction on copper appears to be inhibited by chloride in the presence of corrosion accelerators, NO2 - and Cu+/Cu2+, which suggests that the chloride adlayer remains intact under more aggressive conditions and lowers the rate of corrosion from nitrate reduction in the presence of other oxidants.

Nuclear power is a clean, safe, and economical energy source and after hydrothermal-powered sources, it is the second largest contributor to low-emitting electricity. However, the continuous usage of nuclear power entails the obligation to deal with the long-term management of used nuclear fuel. To do so, Canada plans to use a deep geological repository (DGR) system that will be built approximately 500-800 meters underground in Wabigoon Lake First Nation and the Township of Ignace, Ontario. The DGR consists of corrosion-resistant used fuel containers (UFCs) and other barriers, and it is expected to provide safe and long-term containment of radioactive waste. However, it is essential to consider the eventual failure of the UFCs which can expose fuel to groundwater and pose potential risks. Most of the radionuclides within the used fuel are trapped inside the fuel matrix and the fuel dissolution rate in groundwater determines how fast they can be released into the environment. The containers are expected to remain intact for a long time and any potential breach is likely to occur after β- and γ-radiation have largely decayed. This makes α-radiation the dominant radiation source at the fuel surface and a primary focus. The α-irradiation can cause accumulated radiation-induced damage to the fuel matrix and a possible scenario in this case is the formation of soluble U VI . This can increase the fuel’s dissolution rate as U VI is more soluble than U V and U IV by several orders of magnitude. Therefore, it is necessary to understand the direct effects of high-energy α-particles on the surface of UO 2 -based fuels, as these interactions may influence the fuel dissolution rate. This study uses a novel approach to investigate the effects of α-particles on UO 2 -based fuels via in-situ α-irradiation-electrochemistry experiments. This approach enables studying the surface oxidation state of the fuel in a thin-layer configuration exposed to α-irradiation. The method utilizes UO 2 thin film samples and the Tandetron Accelerator’s Rutherford backscattering beamline to deliver the high-energy high-flux α-particles. To prepare UO 2 thin films, electrodeposition parameters were first optimized via comprehensive characterization of the films deposited on copper substrates to assess their morphology, elemental composition, phase, and crystal structure. Overall, it was found that using less-negative potentials and current densities is optimal for achieving stable films with smaller cracks, better adherence, and higher crystallinity after annealing. UO 2 thin films were then deposited on copper-coated SiN windows using optimized electrodeposition parameters, and the samples were subsequently integrated into a custom-designed in-situ cell for α-irradiation-electrochemistry experiments. Investigations of the effects of high-energy α-particles via in-situ α-irradiation-electrochemistry experiments are currently underway. The surface oxidation states of UO 2 films after α-irradiation will be studied and the effects of α-irradiation on dissolution rate, surface morphology, and phase structure of the UO 2 samples will be presented.

Scanning electrochemical microscopy (SECM) is a powerful technique for analyzing the local electrochemical reactivity of surfaces. The effect of electrolyte concentration is often overlooked but can be a critical parameter to consider when exploring active substrates due to its influence on the corrosion reactions taking place. In this study, hexaammineruthenium(III) chloride was employed as a redox mediator (RM) to investigate the feedback (FB) response over a corroding Cu substrate under various concentrations of sodium chloride electrolyte. At high chloride concentrations (e.g., 600 mM), the FB response rapidly transitioned towards negative behavior due to the fast depletion of RM, which accelerated the substrate's corrosion rate. The kinetic rate constant obtained using a finite element model for the RM's reaction at the Cu surface over time revealed a gradual decrease in surface electroactivity due to the RM reaction with the metal. By diluting the chloride concentration (e.g., <10 mM), the open-circuit potential of Cu shifted to a more positive value than the RM's redox potential, minimizing the oxidizing behavior of the RM towards Cu. As a result, reducing the electrolyte concentration prolonged positive FB behavior for a longer duration, enhancing the reliability of SECM imaging for corrosion studies.

Scanning electrochemical microscopy (SECM) is a popular tool to study corrosion with high spatial resolution. The feedback mode of SECM involves the use of an added redox mediator in solution to probe local surface kinetics. Depending on the redox mediator's oxidation state and formal potential, as well as the corroding metal's corrosion potential, the electroactive species can potentially polarize the substrate and alter the corrosion behavior at the macro and/or microscale. Therefore, the choice of redox mediator is material dependent. This study explored the use of methyl viologen (MV) as a potentially ideal redox mediator for studying the local reactivity of copper. The SECM solutions were deaerated prior to SECM approach curve measurements to avoid a convoluted response from the oxygen reduction reaction at the ultramicroelectrode. Since the formal potential of MV is lower than the corrosion potential of Cu and undergoes oxidation to regenerate at the substrate's surface, the redox mediator was successfully implemented for kinetic measurements without inducing oxidative etching, ultramicroelectrode fouling, or macroscale corrosion. This work highlights the importance of redox mediator choice for SECM corrosion studies to avoid misinterpretation of data and provides a systematic method of making such decision for accurate measurements.

The corrosion of copper coatings fabricated by electrodeposition and cold-spray deposition in both a pristine and thermally pre-oxidised state was investigated in sulfide solution. Samples were characterised using electrochemistry, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. No major differences were identified in the electrochemical measurements or morphology of the surface film between the two copper coatings post experiments. While sulfur (which is presumed to be sulfide) was found to be present in the pre-existing defects within the shallow subsurface of the cold-sprayed copper material, in this short-term testing, sulfide penetration did not occur within the copper metal matrix in electrodeposited or cold-spray copper.

This study explored the effects of atmospherically formed surface films and surface roughness on Cu corrosion behavior. A comprehensive suite of surface analysis techniques, including X-ray photoelectron spectroscopy, scanning electron microscopy, contact angle measurements, and confocal microscopy, were utilized to characterize the physicochemical properties of the surface films formed over 30 days. Then, both macroscale and droplet electrochemical measurements, such as open circuit potential and linear sweep voltammetry, were performed to explore the films’ effects on the aqueous and atmospheric corrosion behavior of Cu respectively. The results showed that the polarization resistance measured within the droplets was lower than that observed in macroscale experiments, attributable to the varying oxygen diffusion profiles. During atmospheric corrosion, the polarization resistance was dependent on the surface finish due to its impact on the film's composition. Surface characterization revealed the formation of hydroxide and defect oxides that varied between the different surface finishes, resulting in differences in polarization resistances over a 30-day period. However, the films did not affect the polarization resistance measured for samples that underwent aqueous electrochemical corrosion testing, possibly due to their solubility during the open circuit potential period prior to reaching a steady state. This study underscores the importance of surface films on atmospheric corrosion properties and brings skepticism to the need for cathodic cleaning of Cu during aqueous corrosion studies under aerated conditions.

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since the HLW/SF canisters are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of the long-term corrosion behaviour, including models for uniform and localized corrosion, environmentally assisted cracking and microbiologically influenced corrosion. As well as process models focused on specific corrosion mechanisms (described in Part 1 of this review), there is also a need for performance assessment models as part of the overall analysis of the safety of a deep geological repository (DGR). Performance assessment models are often based on simplified or abstracted process models. The manner in which various international waste management programs have predicted the long-term performance of HLW/SF containers with copper, steel, Ni and Ti alloy corrosion barriers is discussed. Performance assessments are repeated periodically during the development and implementation of a DGR, and the corrosion models are constantly updated in light of new mechanistic understanding and/or more information about the deep geological environment. Two examples of how the container performance assessment models evolve over time are also described. Performance assessment models cannot easily be validated, so it is important to build confidence in the long-term predictions using other methods, including natural analogues and large-scale in situ tests and the use of complementary models.

The Canadian deep geological repository (DGR) design consists of copper coated used fuel containers (UFCs) placed within a highly compacted bentonite (HCB) buffer surrounded by a suitable host rock. Although the copper is thermodynamically stable in oxygen-free environments, it is potentially susceptible to microbiologically influenced corrosion from bisulfide (HS-). Therefore, understanding HS- corrosion is important to ensure long-term performance of UFCs. Various reactions in the bentonite barrier of the DGR can affect HS- transport through the HCB and therefore the extent of copper corrosion caused by HS-. Since HS- transport and reactive processes are interconnected, numerical models are required to assess the complex HS- reactive transport dynamics and quantify the influence of reactive processes on HS- transport and corrosion. In this paper, various HStransport models were coupled with (i) a key geochemical reaction between HS- and iron (i.e., simulating HSretardation due to iron sulfide formation) or (ii) HS- adsorption. Since HS- is an anion, anion exclusion was also explored. Valuable insight was obtained through validation, comparison, and sensitivity analyses of these models. A comparison between experimental and modelled HS- transport dynamics showed that HS- is being retained by the bentonite due to reactive processes and anion exclusion is occurring. Lastly, HS- transport was simulated for the entire DGR lifespan and was found to be delayed (approximate to 50-800 years) due to FeS formation or HSadsorption. However, these predicted HS- diffusion delays are relatively short in a DGR lifespan (i.e., 1 million years) and do not impact long-term HS- corrosion.

Scanning electrochemical microscopy (SECM) is widely used to measure local electrochemical reactivity of corroding surfaces. A major criticism of using SECM in feedback mode for corrosion studies is the requirement of an external redox mediator (RM) as it could react with the metal and affect the Nernst potential at the metal-solution interface. Consequently, it becomes challenging to differentiate the interference caused by the RM from the local reactivity of the metal. Herein, a multiscale electrochemical approach is presented to investigate the effect of RM choice on the corroding substrate. Two common RMs, ferrocenemethanol and hexaammineruthenium(III) chloride, were used to perform SECM over copper and aluminum. It was found during macroscale electrochemical measurements that Ru(NH)63+ acted as an oxidant and promoted corrosion. The SECM feedback behavior varied for copper depending on the RM used, suggesting that the corrosion reactions controlled the negative feedback mechanism, not the formation of an insulating passive film. The passivated aluminum surface consistently exhibited negative feedback, regardless of the RM used. SECM approach curves also displayed a distortion in the steady state current, which was caused by the deposition of substrate-generated species on the microelectrode. These deviations in feedback response were accounted for during analysis through incorporation into a finite element model to accurately extract the RM kinetic rate constants. The importance of understanding these processes is highlighted to avoid misinterpretation of passive behavior and advances toward a more quantitative use of SECM for corrosion studies.

Canada's deep geological repository (DGR) design includes an engineered barrier system where highly compacted bentonite (HCB) surrounds the copper-coated used fuel containers (UFCs). Microbial-influenced corrosion is a potential threat to long-term integrity of UFC as bisulfide (HS-) may be produced by microbial activities under anaerobic conditions and transported via diffusion through the HCB to reach the UFC surface, resulting in corrosion of copper. Therefore, understanding HS- transport mechanisms through HCB is critical for accurate prediction of copper corrosion allowance. This study investigated HS- transport behaviour through MX-80 bentonite at dry densities 1070-1615 kg m(-3) by performing through-diffusion experiments. Following HS- diffusion, bromide (Br-) diffusion and Raman spectroscopy analyses were performed to explore possible physical or mineralogical alterations of bentonite caused by interacting with HS-. In addition, accessible porosity (epsilon) was estimated using extended Archie's law. Effective diffusion coefficient of HS- was found 2.5 x 10(-12) m(2) s(-1) and 5.0x 10(-12) m(2) s(-1) for dry densities 1330 and 1070 kg m(-3), respectively. No HS- breakthrough was observed for highly compacted bentonite (1535-1615 kg m(-3)) over the experimental timeframe (170 days). Raman spectroscopy results revealed that HS- reacted with iron in bentonite and precipitated as mackinawite and, therefore, it was immobilized. Finally, results of this study imply that HS- transport towards UFC will be highly controlled by the available iron content and dry density of the buffer material.

This work presents a new methodology to estimate the surface area of the working electrode during scanning electrochemical cell microscopy (SECCM) in situ by utilizing retraction curves. In this approach, the current is measured as a function of pipet displacement in the z-direction. When the current drops to zero, it is indicative of droplet detachment from the surface, allowing for the estimation of the droplet contact diameter based on the pipet displacement. This enables real-time estimations of surface areas of the wetted electrode at each point of measurement, rather than performing time-consuming measurements using ex situ correlative image analysis or estimating an average working electrode size from the pipet aperture. Notably, during SECCM measurements on copper in nitric acid, the working electrode diameter estimated using retraction curves was significantly smaller than the droplet footprint diameter observed post experiment using ex situ correlative image analysis. This discrepancy is attributed to droplet spreading after pipet retraction, as confirmed by goniometer and silanized pipet measurements. Upon cleaning the surface, the true wetted surface areas during SECCM measurements were found to be in good agreement with values estimated using retraction curves yet were larger than the pipet aperture. Additionally, the effects of approach separation, retraction rates, and probe diameter on the droplet contact size were analyzed using retraction curves. These findings were compared to ex situ methods to assess the reliability of the retraction curves for determining the working electrode surface area. This study demonstrates the potential of retraction curves to provide a higher accuracy in the quantitative analysis of local current density values extracted using SECCM.

The Nuclear Waste Management Organization of Canada has adopted an adaptive phased management plan for the long-term storage of used nuclear fuel in a Deep Geological Repository (DGR). The DGR barrier system employs copper-coated used fuel containers (UFCs) surrounded by buffer material which is composed of highly compacted bentonite clay. The natural organic matter (NOM) composition of the compacted bentonite is of practical importance for the safety assessment as it regulates the biogeochemical processes at the interface between the UFCs and the buffer layer. However, insufficient investigations on NOM constituents limits the understanding of biogeochemical dynamics in bentonites compacted under different dry densities. This study analyzed the carbon content and NOM composition using targeted compound analysis and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy with bentonites compacted at 1.1, 1.4 or 1.6 g/cm(3) dry density for 1, 3, 6, 12 or 18 months. Organic carbon contents were similar across bentonites with different compaction densities at various durations as compared to the reference clay (powdered bentonite sample before compaction). The overall NOM composition measured by solid-state C-13 NMR suggested a predominance of alkyl and aromatic carbon in bentonite samples. No marked variations were observed for the NOM components (i.e., alkyl, O-alkyl and aromatic carbon) between the compacted bentonites and the reference clay. Targeted compound analysis revealed that the extractable lipid concentrations in the compacted clays did not significantly vary from the reference bentonite with only some compounds exhibiting nano-gram level differences. Bentonites with relatively lower dry densities (1.1 and 1.4 g/cm(3)) demonstrated slightly higher extractable compound concentrations, but these differences were not statistically significant. In contrast, the compound concentrations of bentonites compacted to 1.6 g/cm(3) were similar or slightly lower compared with the reference bentonite, likely associated with limited microbial growth under high dry compaction density. Taken together, these results suggested that NOM composition and quantity did not significantly alter in bentonites under various pressures nor with longer experimental durations. These findings highlight that compacted bentonite exhibited geochemical stability under the simulated repository environments, which provides critical insight for design and performance of engineered barrier system in a DGR concept.

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since HLW/SF containers are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of long-term corrosion behaviour, including models for uniform and localised corrosion, environmentally assisted cracking, microbiologically influenced corrosion, and radiation-induced corrosion. More recently, fracture-mechanics-based approaches have been developed to account for joint mechanical–corrosion degradation modes. Regardless of whether empirical or deterministic models are used, it is essential to be able to demonstrate a thorough mechanistic understanding of the corrosion processes involved. In addition to process models focused on specific corrosion mechanisms, there is also a need for performance-assessment models as part of the overall demonstration of the safety of a deep geological repository. Performance-assessment models are discussed in Part 2 of this review.

The Nuclear Waste Management Organization (NWMO) is planning to develop a deep geological repository (DGR) for safe and long-term management of Canada’s used nuclear fuel in a stable rock formation 500 m below ground surface. Within a DGR, the used nuclear fuel will be encapsulated in an engineered barrier system (EBS), which will include copper-coated used fuel containers (UFCs) surrounded by highly compacted bentonite (HCB). A potential concern towards the long-term EBS performance is the production of bisulphide (HS−) by sulphate-reducing bacteria near the rock-bentonite interface. If produced, HS− may diffuse through the bentonite and corrode the copper surface of the UFC. Although it is anticipated that sorption onto bentonite will restrict HS− transport and minimize the risk of corrosion, the sorption phenomenon of HS− onto bentonite has not been systematically investigated in the hydrogeochemical context of a DGR. To address this knowledge gap, this study designed laboratory batch experiments to investigate HS− sorption onto bentonite under the influence of various conditions relevant to a DGR. As a part of this study, a literature review was conducted to select the factors that may influence the sorption behaviour. The study also required robust methodology development to build confidence in the experimental procedure. The preliminary results showed that sorption process required 24 h to reach equilibrium at room temperature (22 ± 2 °C). In addition, a minimum: (i) liquid-to-solid ratio of 100:1 and (ii) 1 ppm initial HS− concentration were required to obtain detectable amounts of aqueous HS− after sorbing onto bentonite. Considering the experimental constraints and the expected range of the key geochemical conditions in the DGR (e.g. temperature, pH, ionic strength), four sets of batch experiments were designed with appropriate quality control to explore the sorption phenomenon (including kinetics, isotherms, thermodynamics) under the key factors. While this study sheds light on the fundamental sorption mechanisms in bentonite; it also provides valuable guidance on sorption experimental methodology, which can be used in other environmental related research. Altogether, this study supports the broader, ongoing effort to assess the long-term EBS performance of Canada’s DGR.

This paper examined the effect of surface preparation on the corrosion behaviour of copper coatings produced by electrodeposition and cold spray (CS) techniques. These methods are intended to be used to apply a copper coating on the used fuel containers as one of the multi-barrier layers to safely manage spent nuclear fuel long term in a deep geological repository (DGR). The as-received Cu samples exhibit significant variations in their surface chemistry and topography when compared to the polished samples. Furthermore, the microstructure and morphology of the CS coatings may not be homogeneous throughout their thickness. This study also examined the effect of polishing to different depths within the CS coatings on their resulting corrosion behaviour. To investigate the effect of surface preparation on the coatings’ corrosion properties, electrochemical measurements and complementary surface analysis techniques, such as Raman spectroscopy, X-ray micro-computed tomography (μ-CT), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), were employed. Consequently, it was observed that polishing the samples resulted in a more negative corrosion potential and an increase in corrosion current density, caused by the removal of the outer surface oxide layer formed during coating fabrication. However, there was no significant difference in the corrosion behaviour of Cu coatings and wrought Cu. Furthermore, despite the uneven distribution of voids and oxides throughout the CS coating, the corrosion properties were consistent. Therefore, it was concluded that polishing significantly changed the corrosion properties of as-received coatings, while the corrosion behaviour of the CS coating was almost homogenous through its depth.

The corrosion of wrought, electrodeposited, and cold spray deposited copper was electrochemically monitored for ~160 days in 3M NaCl solution containing traces of sulfide under anoxic and Ar-purged conditions. Corroded specimens were analyzed using scanning electron microscopy and Raman and X-ray photoelectron/Auger spectroscopies. Under anoxic conditions, corrosion was supported by sulfide only and the rate decreased with time causing only minor damage. Under low oxygen conditions maintained by Ar-purging, the rate increased with time and significant damage was observed, attributed to oxy-sulfur species formation. These results suggest that oxy-sulfur species, not just sulfide, are required to cause intergranular corrosion.

Over the past decade, the Nuclear Waste Management Organization has conducted a thorough proof test plan (PTP) to evaluate their novel copper-coated used fuel container and bentonite buffer box underground emplacement concept for use in a deep geological repository (DGR). This PTP has included the development of new technologies as well as feasibility studies related to engineered barrier production, underground emplacement, and safety assessment of the technologies within a DGR. Although the PTP was winding down in 2022, many work packages continue, particularly those associated with the evaluation of the corrosion performance of the used fuel container, the Nuclear Waste Management Organization (NWMO)'s copper corrosion allowance. This work evaluates the extent of corrosion that may result from oxic-, radiolytic-, anoxic-, and sulfide-induced corrosion which may occur in the Canadian DGR. Particular attention is paid to assessing the potential for localized corrosion phenomena across each project. This article provides an overview of these work packages which support a lifetime corrosion expectation of 270 mu m and an extreme upper bound of corrosion of 1204 mu m over one million years.