Corrosion Related to the Nuclear Waste Containers

The disposal of nuclear waste is a demanding topic, and the existing methods, whether it is temporary storage in spent fuel pools or storage in geological repositories, both face the risk of corrosion-related problems. Any failure in these storage methods can potentially lead to the release of radioactive materials into the environment. To avert such catastrophic scenarios, people in the nuclear industry consistently monitor and maintain these storage facilities endlessly and attempt to improve the plans designed to store nuclear waste. Here, I will examine the nuclear waste management organization (NWMO) plan in Canada. Choosing an appropriate location for the construction of a deep geologic repository (DGR) for high-level nuclear waste is a challenging process that often generates social conflicts, and only a handful of countries have been able to navigate this process successfully, and Canada is currently on the brink of making such a decision

Advisory Board Members

For SSHRC funded projects, the Applicant, now Principal Investigator (PI), has responsibility for the direction of the project and all financial expenditures. Consistent with this requirement, the CBERN/SSHRC proposal contains two Governance elements. First, the Principal Investigator is required to report to an annual meeting whose membership includes co-applicants, now co-investigators, collaborators and partners, on financial expenditures, project activities and strategic planning. In addition, the proposal calls for the establishment of an Advisory Board, which is to meet at least twice yearly, in person at the Annual Meeting and by telephone conference mid-way through the year. Initial membership and structure of the Advisory Board was set out in the proposal

Talking about gas generation

Dr Richard Shaw currently dedicates his work to a long-term view of radioactive waste management, specifically trying to understand how its waste gases move in deep geological repositories. Here, he explains the huge scope of the FORGE project, and its heavily collaborative approac

Electrochemical and Modelling Studies on Simulated Spent Nuclear Fuel Corrosion under Permanent Waste Disposal Conditions

The safety assessment models for the deep geological disposal of spent nuclear fuel require a fundamental understanding of the corrosion of spent fuel in a failed waste container. The overall research goal of this project is to investigate the corrosion of simulated spent fuel under permanent disposal conditions, using both model simulations and experimental investigations. A model for fuel corrosion has been expanded to determine the relative importance of radiolytic hydrogen and hydrogen from corrosion of the steel vessel in suppressing fuel corrosion. It was shown that, for CANDU (CANada Deuterium Uranium) fuel with moderate in-reactor burnup, only micromolar concentrations of hydrogen from steel corrosion are required to completely suppress fuel corrosion. In a partially closed system (i.e., within cracks in the fuel) radiolytic hydrogen alone can suppress corrosion to a negligible level. The model was validated by comparing the calculated corrosion rates with published measurements. Agreement between calculated and measured rates indicated that corrosion is controlled by the rate of radiolytic production of oxidants, in particular hydrogen peroxide, irrespective of the reactivity of the fuel. Experimentally, the influence of rare earth doping on the reactivity of UO2 was investigated. For REIII-doped UO2, the onset of matrix dissolution was accompanied by the enhanced oxidation of the matrix to UIV1−2xUV2xO2+x. This can be attributed to the onset of tetragonal lattice distortions as oxidation proceeds which leads to the clustering of defects, enhanced diffusion of OI (interstitial oxygen)to deeper locations and destabilization of the fluorite lattice. A further investigation of the doping effect was performed on a series of (U1−yGdy)O2 materials (y = 0, 0.01, 0.03, 0.05, 0.07 and 0.10). Overall the increase in doping up to 10% does not exert a major influence on reactivity possibly due to the competition between an increase in the number of (Ov)s (oxygen vacancy) and a contraction in the lattice constant

The Electrochemistry of Hydrogen Peroxide on Uranium Dioxide and the Modelling of Used Nuclear Fuel Corrosion under Permanent Disposal Conditions

This thesis reports a series of investigations examining the corrosion process of used nuclear fuel under permanent disposal conditions. The motivation of the project is that the safety assessment of deep geological disposal of spent nuclear fuel requires a fundamental understanding of the processes controlling fuel corrosion which could lead to the release of radionuclides to the geosphere from a failed container. One primary objective of this project was to develop a computational model in order to simulate fuel corrosion under the disposal conditions. A series of simulations based on COMSOL were designed and developed to determine the influence of redox conditions, with the emphasis on α-radiolysis and steel vessel corrosion products, on the corrosion rate of spent fuel. A second objective of this project was to develop a more detailed understanding of the H2O2 decomposition process and its influence on UO2 (nuclear fuel) corrosion. The radiolytically produced H2O2 is the primary driving force for nuclear fuel corrosion under disposal conditions. The influence of several variables (potential, pH, carbonate/bicarbonate, and fission products) on the reactivity of H2O2 has been evaluated. Their influence on the surface composition and electrical conductivity of UO2 was found to significantly affect the surface redox reaction rates and alter the overall fuel corrosion rate. The analytical techniques include electrochemical measurements (CV, CSV, ECORR, LPR, EIS) and surface/solution analyses (SEM, XPS, ICP-AES)

Canada's Nuclear Crossroads: Steps to a Viable Nuclear Energy Industry

Canada is at an energy and environmental crossroad. Fossil fuels cause environmental damage and the growth potential of large-scale hydroelectricity is limited. Policymakers are reconsidering the merits of nuclear power as both a low-carbon emitting and low-cost base load electricity source. While nuclear power may look like an attractive option, nuclear power must overcome problems such as the high and uncertain cost of construction, dealing with nuclear waste, reactor licensing and regulation, and the future of Canada’s nuclear reactor builder, Atomic Energy of Canada Limited (AECL), a federal Crown corporation.economic growth and innovation, energy and environmental policy

MICROBIAL ABUNDANCE, DIVERSITY, AND POTENTIAL ACTIVITY IN BENTONITE CLAY

The Canadian deep geologic repository (DGR) concept for long-term safe storage and isolation of used nuclear fuel incorporates a multi-protective engineered barrier system. However, due to the inevitable presence of microorganisms and their metabolic products in a DGR, the integrity of the containers, and hence the repository, might be compromised. Therefore, the emphases of this thesis are to characterize and identify the microbial populations present in bulk and highly-compacted Wyoming MX-80 bentonite, to determine the conditions under which the survival and activity of microorganisms in highly-compacted bentonite clay (one of the engineered barriers) will be minimized or regulated, and to observe the microbial capacity to interact with bentonite particle under nutrient regime (clay-microbe aggregation study). To achieve these, culture-dependent and molecular biology methods (e.g., 16S rRNA sequencing), a range of analytical chemistry assays (e.g., sulfate turbidimetric method), pressure cell studies, microscopic technique (e.g., confocal laser microscopy (CLSM)), particle size analyses and laboratory-scale enrichment (or microcosm) assays were carried out. Culture-dependent techniques revealed the presence of spore-forming bacterial isolates belonging to phyla Actinobacteria and Firmicutes in bulk MX-80. Interestingly, when MX-80 bentonite was highly compacted, Gram-positive spore-formers were also identified after being exposed to the collective effect of > 2,000 kPa swelling pressure, 0.96 water activity, oxygen-free environment, and ≥ 1.6 g/cm3 dry density conditions for ~ 145 days and ~ 8 years. It was determined that microbial culturability was suppressed at or below background level (i.e., ≤ 2 x 102 Colony Forming Units per g) when the aforementioned parameters were applied and when 50 g/L NaCl solution infiltrated the highly-compacted bentonite (HCB). Sulfate reducing bacteria (SRB) in the HCB, however, were speculated to remain as spores during the incubation period since their microbial counts were similar at different dry densities. The enrichment assays for SRB containing bentonite clay slurry amended with carbon, electron donors and acceptors revealed that lactate was the preferred substrate for sulfidogenesis and that high salinity could impede the same process. Finally, the clay-microbe aggregation study showed that extracellular polymeric substance (EPS) contribute to the clay-microbe aggregation and that nutrient concentration, carbon substrate type and bentonite concentration affect EPS production. Overall, these studies are relevant to DGR operations because the results obtained will assist in understanding the potential consequences of microbial interactions with clay minerals

分子動力学法を用いた水/xNa2O-(1-x)SiO2(x=0~0.5)ガラス界面の構造解析

Weathering of glass is a problem because it degrades the optical performance of the glass. The weathering occurs when the glass has been contacted with water in the long-term. In this work, a water/glass interface model was prepared and molecular dynamics simulation was performed to investigate the structure and properties near the water/glass interface. The broken surface of the glass network at near the interface was confirmed by the distribution change of the Qn species, and it suggests that the sodium ions are trapped by the destabilized glass surface structure