Exploring the Use of Covellite as a Proxy for Corrosion of Native Copper by Sulphur Reducing Bacteria

We are analyzing the effect of sulphate reducing bacteria on native copper, and using that evidence to further support the initiative of having a deep geological repository to store nuclear material. Sulphate reducing bacteria are a concern for the deep geological repository as they cause the corrosion of regular copper. However native copper has gone billions of years without corrosion, which could either mean that it had not been exposed to sulphate reducing bacteria over the billions of years, or native copper is able to withstand corrosion despite the contact of sulphate reducing bacteria. We can find out by trying to find the biomarkers of sulphate reducing bacteria on native copper, which through literature search are found to be copper sulphide also known as Covellite. By using an electron microscope to search for Covellite on the native copper sample, we can determine if, and how sulphate reducing bacteria affects native copper. A further application of this experiment would be to see how to implement this characteristic of native copper onto the copper used in the deep geological repository

Microbial Effects on Repository Performance

This report presents a critical review of the international literature on microbial effects in and around a deep geological repository for higher activity wastes. It is aimed at those who are familiar with the nuclear industry and radioactive waste disposal, but who are not experts in microbiology; they may have a limited knowledge of how microbiology may be integrated into and impact upon radioactive waste disposal safety cases and associated performance assessments (PA)

Chemical and structural characterization of SeIV biotransformations by Stenotrophomonas bentonitica into Se0 nanostructures and volatiles Se species

Microorganisms such as Stenotrophomonas bentonitica could influence the safety of the deep geological repository system by producing nanoparticles and volatile compounds of selenium

From cradle to grave? : On optimal nuclear waste disposal

This paper analyses socially optimal nuclear plant operation and nuclear waste management. Two waiting rules are derived: the first characterizes the optimal continuation of electricity production, and the second gives the optimal nuclear waste disposal date. Both rules balance the cost and benefit of either continuing production or delaying waste disposal into a deep geological repository. In addition, multiple regulatory options are investigated. The optimized waste storage and disposal cost forms the payment that should be collected from the nuclear power firm into a nuclear waste fund. The properties of this payment and other regulatory options including a tax to be paid at the shutdown date of the plant are investigated, and it is shown that the money can be collected by a plant-specific constant fee targeted at firm's profit or output. Numerical illustration shows that waste disposal to a deep geological repository is a cost-minimizing solution only with very low interest rates. For interest rates above one percent it is optimal to store the waste in an on-ground storage facility in perpetuity.Peer reviewe

Effect of U(VI) aqueous speciation on the binding of uranium by the cell surface of Rhodotorula mucilaginosa, a natural yeast isolate from bentonites

This study presents the effect of aqueous uranium speciation (U-hydroxides and U-hydroxo-carbonates) on the interaction of this radionuclide with the cells of the yeast Rhodotorula mucigilanosa BII-R8. This strain was isolated from Spanish bentonites considered as reference materials for the engineered barrier components of the future deep geological repository of radioactive waste. X-ray absorption and infrared spectroscopy showed that the aqueous uranium speciation has no effect on the uranium binding process by this yeast strain. The cells bind mobile uranium species (U-hydroxides and U-hydroxo-carbonates) from solution via a time-dependent process initiated by the adsorption of uranium species to carboxyl groups. This leads to the subsequent involvement of organic phosphate groups forming uranium complexes with a local coordination similar to that of the uranyl mineral phase meta-autunite. Scanning transmission electron microscopy with high angle annular dark field analysis showed uranium accumulations at the cell surface associated with phosphorus containing ligands. Moreover, the effect of uranium mobile species on the cell viability and metabolic activity was examined by means of flow cytometry techniques, revealing that the cell metabolism is more affected by higher concentrations of uranium than the cell viability. The results obtained in this work provide new insights on the interaction of uranium with bentonite natural yeast from genus Rhodotorula under deep geological repository relevant conditions

Two phase partially miscible flow and transport modeling in porous media: application to gas migration in a nuclear waste repository

We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water saturated repository

Use of thermodynamic adsorption models to describe geochemical processes under deep geological repository environments

Deep geological repositories are the most widely accepted international solution to dispose of high activity radioactive wastes. This solution requires an exhaustive analysis of the different containment barriers that will have to isolate these radionuclides for thousands of years so that they are not released into the biosphere prematurely. The last barrier is the geological environment and one of the most important properties that this barrier has is its capacity to retain radionuclides through sorption processes. On the other hand, transuranic elements such as americium or curium are one of the radionuclides with the longest life and radiotoxicity. However, studying these elements is neither easy nor cheap, so the sorption of these elements is usually studied using other more common ones that serve as an analog, europium being the most used. The models used today to describe radionuclide sorption are usually complex, which makes them very sensitive and specific to the conditions used in the experiments, as well as, in some cases, requiring large computational capabilities. Throughout this work we have tried to see how far the sorption models can be simplified. To this aim, we have developed PHREQC-based sorption models capable of explaining europium sorption in illite mineral matrices. As a result, three models have been obtained. Two of which allow simulating some experimental cases without the presence of carbonates within pH ranges between 4 and 10, as well as in concentrations less than 10-6M of europium dissolved in the medium. The last model makes possible to reproduce the sorption of europium in the presence of carbonates within a pH range between 6 and 10, as well as in concentrations less than 10-6M of europium dissolved in the medium

Evaluation of Swelling Pressure and Shear Strength of Inorganic Microfiber-Reinforced Bentonite for the Engineered Barrier System

Nowadays, the permanent disposal of high-level radioactive waste materials has been a primary concern in several countries. The deep geological repository, being the preferred disposal method across the globe, utilizes a network of engineered barriers to prevent the radioactive material from spreading throughout the facility and harming the natural environment. Part of this engineered barrier system (EBS) is the buffer material, which essential function is holding the radioactive waste-containing canister in place. However, the potential generation of desiccation cracks in this buffer material is imminent due to the heat emitted from the radioactive waste. Knowing the capability of inorganic fibers to help mitigate such a situation, glass microfiber is proposed as a reinforcement material to bentonite, owing to its high heat resistance. This research aims to evaluate the effect of fiber content on bentonite in terms of swelling pressure and shear strength. Using the one-dimensional consolidation test setup, the swelling pressure test was conducted at both ambient and elevated temperatures to obtain the swelling pressure and compressibility characteristics of the inorganic-microfiber reinforced bentonite. Moreover, the shearing behavior of the bentonite sample was observed through the direct simple shear test. Lastly, the specimen’s behavior under the critical state was predicted using the Modified Cam Clay Model. The results obtained from this study would be a valuable tool for the baseline assessment of the effectiveness of the fiber reinforcement to potentially improve the engineering performance of the deep geological repository for the safe storage of high-level radioactive waste materials. Advisors: Jongwan Eun and Seunghee Ki

Status and development of deep geological repository in Slovak republic from geological point of view

During the operation of Slovak NPPs, production of approximately 2,300 metric tons of spent fuel expressed as heavy metal (18,654 spent fuel assemblies) is expected. In addition, about 5000 metric tons of radioactive waste unfit for near surface repository at Mochovce and destined for a deep geological disposal. The safe and long-term solution of back-end fuel cycle is so highly required.One of the most favorable solutions is Deep Geological Repository (DGR). The site for a DGR, along with repository design and the engineered barrier system must ensure long-term safety of the disposal system.A preliminary set of site-selection criteria for a DGR was proposed in Slovakia, based on worldwide experience and consistent with IAEA recommendations. Main groups of criteria are: 1) geological and tectonic stability of prospective sites; 2) appropriate characteristics of host rock (lithological homogeneity, suitable hydrogeological and geochemical conditions, favourable geotechnical setting, absence of mineral resources, etc.); 3) conflict of interests (natural resources, natural and cultural heritage, protected resources of thermal waters, etc.).Based on the previous geological investigations, three distinct areas (five localities) were determined as the most prospective sites for construction of a DGR so far. Three of them are built by granitoids rock (Tribeč Mts., Veporske vrchy Mts. and Stolicke vrchy Mts.), other consist of sedimentary rock formations (Cerova vrchovina Upland and Rimavska kotlina Basin). Objective for the next investigation stage is to perform more detailed geological characterization of the prospective sites

Design Optimization for Spatial Arrangement of Used Nuclear Fuel Containers

Canada's proposed deep geological repository is a multiple-barrier system designed to isolate used nuclear fuel containers (UFCs) indefinitely with no release of radionuclides for at least one million years. Placing UFCs together as densely as possible is ideal for mitigating repository size and cost. However, due to heat generation from radioactive decay and material limitations, a key design criterion is that the maximum temperature inside the repository must not exceed 100 °C. To satisfy that criterion, design optimization for the spatial arrangement of UFCs in a crystalline rock repository is performed. Spatial arrangement pertains to: (i) the spacing between UFCs, (ii) the separation between placement rooms underground, and (iii) the locations of variously aged UFCs that generate heat at different rates. Most studies have considered UFCs to be identical in age during placement into the repository. Parameter analyses have also been performed to evaluate repository performance under probable geological conditions. In this work, the various ages of UFCs and the uncertainties in spacing-related design variables are of focus. Techniques for the actual placement of UFCs in the deep geological repository based on their age and methods for repository risk analysis using yield optimization are developed. The thermal evolution inside the deep geological repository is simulated using a finite element model. With many components inside the massive repository planned for upwards of 95,000 UFCs, direct optimization of the model is impractical or even infeasible due to it being computationally expensive to evaluate. Surrogate optimization is used to overcome that burden by reducing the number of detailed evaluations required to reach the optimal designs. Two placement cases are studied: (i) UFCs all having been discharged from a Canadian Deuterium Uranium reactor for 30 years, which is a worst-case scenario, and (ii) UFCs having been discharged between 30 and 60 years. Design options that have UFC spacing 1–2 m and placement room separation 10–40 m are explored. The placement locations of the variously aged UFCs are specified using either sinusoidal (cosine) functions or Kumaraswamy probability density functions. Yield optimization under assumed design variable tolerances and distributions is performed to minimize the probability of a system failure, which occurs when the maximum temperature constraint of 100 °C is exceeded. This method allows variabilities from the manufacturing and construction of the repository components that affect the design variables to be taken into account, incorporating a stochastic aspect into the design optimization that surrogate optimization would not include. Several distributions for the design variables are surveyed, and these include uniform, normal, and skewed distributions—all of which are approximated by Kumaraswamy distributions