Nuclear Waste Storage Research Articles

Enhancing the Performance of a Large Aperture Ultrasound System (LAUS): A Combined Approach of Simulation and Measurement for Transmitter-Receiver Optimization.

The Large Aperture Ultrasound System (LAUS) developed at BAM is known for its ability to penetrate thick objects, especially concrete structures commonly used in nuclear waste storage and other applications in civil engineering. Although the current system effectively penetrates up to ~9 m, further optimization is imperative to enhance the safety and integrity of disposal structures for radioactive or toxic waste. This study focuses on enhancing the system's efficiency by optimizing the transducer spacing, ensuring that resolution is not compromised. An array of twelve horizontal shear wave transducers was used to find a balance between penetration depth and resolution. Systematic adjustments of the spacing between transmitter and receiver units were undertaken based on target depth ranges of known reflectors at depth ranges from 5 m to 10 m. The trade-offs between resolution and artifact generation were meticulously assessed. This comprehensive study employs a dual approach using both simulations and measurements to investigate the performance of transducer units spaced at 10 cm, 20 cm, 30 cm, and 40 cm. We found that for depths up to 5 m, a spacing of 10 cm for LAUS transducer units provided the best resolution as confirmed by both simulations and measurements. This optimal distance is particularly effective in achieving clear reflections and a satisfactory signal-to-noise ratio (SNR) in imaging scenarios with materials such as thick concrete structures. However, when targeting depths greater than 10 m, we recommend increasing the distance between the transducers to 20 cm. This increased spacing improves the SNR in comparison to other spacings, as seen in the simulation of a 10 m deep backwall. Our results emphasize the critical role of transducer spacing in achieving the desired SNR and resolution, especially in the context of depth imaging requirements for LAUS applications. In addition to the transducer spacing, different distances between individual sets of measurement positions were tested. Overall, keeping the minimal possible distance between measurement position offsets provides the best imaging results at greater depths. The proposed optimizations for the LAUS in this study are primarily relevant to applications on massive nuclear structures for nuclear waste management. This research highlights the need for better LAUS efficiency in applications such as sealing structures, laying the foundation for future technological advances in this field.

Surrogate models of heat transfer in fractured rock and their use in parameter estimation

Fracture distribution plays a significant role in the behavior of subsurface environments, affecting such activities as geothermal production, exploitation and management of groundwater resources, and long-term storage of nuclear waste and carbon dioxide. A key challenge in these and other applications is to estimate the fracture network properties from sparse and noisy observations. We evaluate the utility of cross-borehole thermal experiments for this task, using both physics-based particle-tracking (PBPT) heat-transfer approach and its deep neural network (DNN) surrogates. Synthetic data are provided by the PBPT simulations and used to train and test the DNN surrogates over a full range of the fracture network properties. We propose regionalized and step-by-step training techniques to reduce the computational cost of expensive PBPT forward solves over large ranges of the (to-be-estimated) parameters. Our numerical experiments suggest the feasibility of training a regionalized DNN surrogate over parameter ranges for which the PBPT solves are fast and extrapolating its predictions to parameter ranges with few additional data. We analyze the balance between computational cost and model accuracy, and provide both PBPT and DNN models for applications to others kinds of data.

Structural properties and failure characteristics of granite after thermal treatment and water cooling

In a variety of fields such as exploitation of geothermal energy and the reconstruction of nuclear waste storage, both of high-temperature and cooling process change the physical and mechanical properties of granite. Uniaxial compression tests were performed on five groups of granite samples at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C after water cooling, and CT scanning, acoustic emission(AE) monitoring and X-ray diffraction(XRD) scanning were used to investigate the structure properties and failure characteristics of granite. It is found that the proportions of pore volume greater than 106 μm3 and less than 105 μm3 with are positively and negatively correlated with the thermal treatment temperature respectively. The mechanical properties of granite are significantly deteriorated by temperature gradient shock, and crack development scale during failure process overall increases as implied by AE response. The failure intensity index η is proposed to characterize the failure severity of granite, and the value of η descends with the increase of thermal treatment temperature, indicating the failure severity of granite is alleviated. Three types of loading failure mode are classified for water-cooled high-temperature granite. The failure mode of granite at 200 °C and 600 °C is tensile failure and tensile-shear failure respectively, while the granite samples are dominated by shear failure at 25 °C, 400 °C and 800 °C.

Development of local-power-free, remote α-particle detection using optical fibers.

We demonstrate the application of fluorescence optical fiber coupled to a telecom grade fiber as a sensor for alpha particles using alpha-specific ZnS(Ag) scintillation materials whose wavelength is down-shifted into a low-loss region of the telecom grade fiber transmission band. Telecom-grade fiber optics offer a solution for sensing alpha radiation in deep repositories and cask storage for radioactive materials due to the stability of SiO2 under normal environmental conditions and its relative radiation hardness at low radiation doses. Long-term nuclear waste storage facilities require sensors for the detection of leakage of radioactive materials that are maintenance-free, do not require power and can survive with no 'wear out' mechanisms for decades. By accomplishing the wavelength transformation, we maximize efficiencies in the detection of α-particles and signal transport and can detect alpha scintillation at distances on the order of >1km with a sensor that is ~3% efficient and can be easily scaled as a sensor array. This paper describes the construction and testing of the sensor including manufacture of the controlled thickness films, verification of the wavelength shift from 450to 620nm and optimization of the sensitivity as a function of thickness. We also model the relative sensitivity of the film as a function of film thickness, and we demonstrate a signal-to-noise ratio of 10 at a range of greater than 1km.

A universal hydro-mechanical coupled behavior model for clay-bearing strata—Molecular-level simulation approach

Clay minerals in soils and rocks exhibit large volume change upon interaction with water and this behavior becomes even more complex when the strata are being stressed by the engineering and environmental loads. Therefore, a realistic prediction of the hydro-mechanical behavior of the clay-bearing strata is always a challenge due to their coupled swelling-mechanical response in the cases of geotechnical and geoenvironmental engineering problems, nuclear waste storage in clay-bearing rock repositories, shale gas extraction, and other uses of clay in the manufacturing industry. All the existing behavior models have restricted applications in the engineering and other fields of practice mainly due to the partial consideration of the structure and fabric of clay-bearing strata in the model formulation. In this study, a hydro-mechanical behavior model has been formulated using the parameters acquired from the molecular-level simulations and modeling of the volume change and stress–strain behavior of the clay-bearing structure. The Molecular Mechanics and Molecular Dynamic simulations were performed on the natural structure of the clay-bearing strata formulated using Monte Carlo technique. The mathematical model, developed from the simulation results, can predict the overall hydro-mechanical behavior of clay-bearing strata for all possible combinations of clay minerals, non-clay minerals, salts causing cementation of the soil/rock structure, confining pressures, and the induced strain levels. The developed model has successfully been validated through laboratory and field testing on the clay-bearing strata in both the elastic and elasto-plastic regions of the stress–strain behavior and also from the data of two (02) swelling clays (MX-80 and FEBEX Bentonite) from the existing literature, supporting the universal nature of the developed behavior model.

Unveiling fungal diversity in uranium and glycerol-2-phosphate-amended bentonite microcosms: Implications for radionuclide immobilization within the Deep Geological Repository system

Uranium (U) represents the preeminent hazardous radionuclide within the context of nuclear waste repositories. Indigenous microorganisms in bentonite can influence radionuclide speciation and migration in Deep Geological Repositories (DGRs) for nuclear waste storage. While bacterial communities in bentonite samples have been extensively studied, the impact of fungi has been somewhat overlooked. Here, we investigate the geomicrobiological processes in bentonite microcosms amended with uranyl nitrate and glycerol-2-phosphate (G2P) for six-month incubation. ITS sequencing revealed that the fungal community was mainly composed of Ascomycota (96.6 %). The presence of U in microcosms enriched specific fungal taxa, such as Penicillium and Fusarium, potentially associated with uranium immobilization mechanisms. Conversely, the amendment of U into G2P-suplemented samples exhibited minimal impact, resulting in a fungal community akin to the control group. Several fungal strains were isolated from bentonite microcosms to explore their potential in the U biomineralization, including Fusarium oxysporum, Aspergillus sp., Penicillium spp., among others. High Annular Angle Dark-Field Scanning Transmission Electron Microscopy (HAADF) analyses showed the capacity of F. oxysporum B1 to form U-phosphate mineral phases, likely mediated by phosphatase activity. Therefore, our study emphasizes the need to take into account indigenous bentonite fungi in the overall assessment of the impact of microbial processes in the immobilization of U within DGRs environments.

The role of core in twenty-first century reservoir characterization: an introduction

Abstract The first two decades of the twenty-first century have seen significant advances across a wide range of reservoir characterization techniques, from microscale digital rock physics to macroscale 3D and 4D seismic. At the same time, industry downturns and the requirements of the energy transition have demanded improved understanding of the value and impact of subsurface data to justify their acquisition and commercial relevance. Despite changing technologies and demands, the acquisition, description and analysis of core remains a fundamental tool in managing subsurface uncertainty and associated risk. Value continues to be created in relation to the reservoir property, sedimentological, diagenetic and structural characterization of subsurface reservoirs, and these are the focus of the Core Values volume. The enduring business impact of core reflects advances in acquisition methods and laboratory-based core analysis (Theme 1 of the volume); the recent development of multi-sensor core scanning and associated artificial intelligence (AI) tools that allow unprecedented high-resolution data collection and visualization (Theme 2); the integration of core-derived data with new complementary technologies, leading to improved characterization of both cored and uncored intervals (Theme 3); the changing nature and role of legacy core collections due to digitization and improved data access (Theme 4). These are complemented by the need to better understand both existing hydrocarbon resources and other subsurface energy-related systems, particularly CCUS (carbon capture, utilization and storage), geothermal energy and the long-term storage of nuclear waste (Theme 5). Through the energy transition core will remain the ground truth foundation to any subsurface understanding and evaluation. At the same time, the technologies available to maximize the applied value of core will continue to develop and evolve, with the integration of diverse and complex core-derived and core-related datasets becoming the norm. Even in the face of AI's impact and value in handling such datasets, those earth scientists who can effectively analyse, interpret and integrate core will still be best placed to meet the subsurface challenges of the future.

Radioactive strontium ions sieving through reduced graphene oxide membrane

Partitioning of 90Sr from other radionuclides in radioactive liquid waste is crucial for treating high-level liquid waste (HLLW) generated during spent fuel reprocessing, as the unique high heat-generating and long half-life of 90Sr pose a significant challenge for the long-term storage of nuclear waste. However, it remains difficult to sieve 90Sr for membrane based on size-selective effect, as the radioactive liquid waste contains numerous typical divalent ions, such as 60Co, 63Ni, and 65Zn, which have the same valence and similar hydration diameters to 90Sr. Here, we experimentally demonstrate a rapid and efficient separation of radioactive 90Sr from other radioactive ions by a reduced graphene oxide membrane, which prepared by the amino-hydrothermal method from graphene oxide suspensions. For SrCl2/CoCl2, SrCl2/NiCl2, and SrCl2/ZnCl2 binary mixed solutions, SrCl2 can pass through efficiently, while the rejection rates for CoCl2, NiCl2, and ZnCl2 reached 99.9 %. The separation factors reached 3232, 4254, and 3314, which are about one or two orders of magnitude higher than the highest reported separation factors for membranes sieving divalent ions. Our findings offer a simple avenue for the precise treatment of radioactive liquid waste, which is vital for the advancement of nuclear energy technology.

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Thermal and mechanical creep of clay in hypoplasticity

Clays and clay soils or shales have attracted a lot of interest in a variety of applications, including the development of geothermal resources [1], energy foundations [2], oil exploration [3], energy storage [4], and the storage of nuclear waste [5]. The continued operation of ground source heat pump installations can lead to considerable long-term settlements, which could negatively affect the adjacent or underlying foundations [1]. Therefore, thermal volume change has been widely experimentally investigated in clays [4, 7, 8, 9]. Especially in [4] the authors studied the thermal and mechanical consolidation of saturated marine clays through laboratory element tests, where excess pore pressures were generated by heating samples at constant water content and then allowed to dissipate. In constant stress creep experiments described in [4] it was documented that thermal creep strains typically increased linearly with log time at rates controlled by the prevailing temperature.
 On the other hand, the mechanical time dependency of the stress–strain behaviour of soft soils, especially highly plastic clay, is generally too significant to be ignored [10, 11]. The constitutive modelling of the time-dependent stress–strain behaviour of soils has been an active area of research for five decades and has attracted much attention from the international geotechnical community in recent years as denoted in [12]. In [13] a visco-hypoplastic (VHP) model for normally and overconsolidated clays has been proposed. Probably the most salient feature of hypoplasticity itself is that loading and unloading can be described with only one equation as with the strain and stress rate denoted as and , respectively. The elastic stiffness tensor is represented by ; is the degree of nonlinearity and is the flow rule (direction of hypoplastic strain). The last part of the equation expresses the time-dependent strain rate (i.e. viscous) with the material parameters as the viscosity index and being the compression index. denotes the overconsolidation ratio. As may be observed, the model is not restricted solely to time-dependent clay materials, because does not represent a singularity for the constitutive equation as in other hypoplastic models. The model has been extended in [14] to account for the small-strain stiffness and the mechanical behaviour under cyclic loading. It follows the critical state theory and incorporates a loading surface for the definition of , see Fig. 1A). Time-dependent one-dimensional behaviour of clays is in most cases explained by the isotache framework, which assumes a unique relation between effective stress, strain, and strain rate in compression, shown as loci of constant strain rate in space, see Fig. 1B). The creep deformation at constant effective stress (; Fig. 1C)) corresponds to a decrease in strain rate of the soil (path A to B in Fig. 1C)). Consolidation stress history, represented by swelling along the path AC, causes a marked reduction in compressive creep rates at low (CD), while expansive/dilative creep strains occur at higher (CEE).
 Due to the temperature dependency of the compressibility of clays the isotachs may be considered as temperature dependent as well. As shown in [6] the isotache loci at a given strain rate for normally consolidated states are functions of strain rate and temperature. Increases in temperature cause additional compressive thermal creep strains for NC and lightly OC states (BB and DD in Fig.1C)) and augment the swelling strains at higher (EE).
 In the framework of hypoplasticity, the non-isothermal behaviour has not gained much attention [15]. This work is devoted to the extension of the VHP model formulation to present a unified model for both thermal and viscous strains in clays. The model predictions are assessed through comparisons with existing laboratory experiments from [7] on two clays with measurements of both isothermal/mechanical creep and thermally induced creep strains, providing a thorough calibration scheme as well.

Public participation in nuclear waste storage and disposal: a comparative analysis of German and US approaches

Abstract. The national nuclear waste management programs of Germany and the United States of America currently both find themselves at critical junctures. The US government is reviving its efforts for consent-based siting of a consolidated interim nuclear waste storage facility (, ), in the momentary absence of, but with future hope for, a viable permanent disposal solution for the nation's nuclear waste. Germany is in the process of implementing legal directives to find a final disposal site for its nuclear waste that meets high safety standards (BASE, 2022), while further developing its strategy for public participation in the process (Weißpflug et al., 2022). The two national contexts exhibit significant differences in political systems, historical trajectories, institutional roles, and societal structure, as well as attitudes towards nuclear energy and radioactive waste disposal strategies (Richter et al., 2022; Saraç-Lesavre, 2021; Joppke, 1993; Blattmann et al., 2023). However, respective approaches to public participation in managing and disposing of nuclear waste exhibit some commonalities in motivations, strategies, and goals. What can policy audiences in both countries learn from the respective national nuclear waste management programs, creating the potential for participatory processes to be more adaptive, responsive, and flexible to a diversity of values and social actors? How do the findings from the comparative analysis of US and German cases translate into policy-relevant lessons for other national waste management programs engaging with the design of participatory processes and nuclear waste governance frameworks? We offer a systematic comparative analysis of the foundations and rationale of the US and German programs for nuclear waste disposal. We aim to illuminate conceptual and empirical contrasts and comparisons between the two nations' engagement of the public in the storage and disposal of spent nuclear fuel, leading to nationally appropriate policy-relevant insights. Categories for analysis include national disposal goals, historical trajectories, institutional setup, and definition of partners in participation processes. Through comparison and contrast of these categories across the two nations, we allow for deeper insight into the conditions, frameworks, and assumptions in which policy makers operate and can draw from Hopkin (2010). This discussion will identify and compare relevant knowledge, narratives, and legal frameworks in each nation's approach to incorporating public participation in the process of searching for a site to store or dispose of nuclear waste. We encourage reflection and learning through comparing and contrasting core principles of these two cases, with the aim of maximizing avenues of mutual learning towards responsible, safe, and democratic nuclear waste management.

Solving problems collectively in nuclear waste governance

Abstract. Nuclear waste governance is a technical and societal task with numerous and complex challenges. The goal is generally accepted and clearly defined, which is that high-level waste is to be stored in a deep geological repository. The path to this goal is determined by the site selection procedure outlined in the Repository Site Selection Act (StandAG). Today (2023), we are in the phase of moving from potentially suitable areas in Germany to a limited number of siting regions. However, selecting a repository site with the best possible safety is only one of the challenges on the way to the final storage of nuclear waste. It can be assumed that the conditions of the social and political framework will change during the decade-long process of site selection, construction, and storage in a repository (Hocke et al., 2021). It is highly probable that unforeseen developments will occur and that a response will be necessary. The entire disposal process must be designed to be flexible so that the central players can remain capable of acting. At the same time, however, it must also be sufficiently robust to allow the process of emplacement in a repository to be completed with as little delay as possible. What precautions need to be taken so that, from the current perspective, the best possible response can be made to unforeseen developments? What decisions will have to be made, and what consequences can be expected? How can path dependencies be avoided (Scheer et al., 2023)? These and other questions were the subject of the 2 d workshop “Nuclear Waste Disposal – Possible Paths, Directional Decisions, Future Challenges”, which was held with a selected group of stakeholders from the field of nuclear waste governance in May 2023. In our contribution, we will present key results of the workshop. The focus of our attention is on the question regarding which problems and perceptions the central actors represented in the workshop focus on and to what extent the experimental setting of the workshop is suitable for promoting collective problem-solving (Werle and Schimank, 2000).

Demonstrating the possibility of safe operation in the first phase of the site selection procedure in Germany

Abstract. The Federal Company for radioactive waste disposal (BGE) is responsible for the search for a site with the best possible safety for the disposal of high-level radioactive waste in Germany. The site selection procedure is regulated in a law that was adopted by the German Federal Parliament (Repository Site Selection Act – StandAG, 2017, last updated 2020 (StandAG)) and aims to be a participatory, transparent, learning, and self-questioning process based on scientific expertise. The first step of the first phase of the site selection procedure was completed in September 2020 and resulted in the identification of sub-areas that give reason for expecting favourable geological conditions for the long-term storage of nuclear waste in the sub-surface. These sub-areas cover approximately 54 % of Germany and are located in three different host rocks: rock salt–halite, claystone, and crystalline rock. The challenge for the next step is to find suitable siting regions within the previously determined sub-areas that are then considered further in the next phase of the site selection procedure (Hoyer et al., 2021). The preliminary representative safety analyses in Phase I, Step 2 of the site selection procedure require according to Section 7 (6) No. 4 EndlSiUntV that “the basic possibility of safe operation shall be demonstrated, but a complete operational safety analysis does not need to be performed”. The method is described in BGE (2022a, b) and can be summarized as follows. The demonstration of the basic possibility of safe operation is carried out within the framework of the representative safety analyses for the individual aspects of operational safety in different degrees of detail. The non-radiological aspects of operational safety, which are, for example, derived from occupational health and safety, mining law and fire protection, a site-independent consideration of the regulatory basis and the derivation of corresponding actions, are considered requirements for and are taken into account by the preliminary repository design according to Sect. 6 (4) EndlSiUntV. To demonstrate the basic possibility of safe operation for the operational safety aspects “radiation protection” and “release of radioactive substances” in the investigation areas to be considered, a general catalogue is compiled that summarizes possible events and actions to fulfill the requirements for operational safety. This general catalogue is independent of location and coverage of all host rocks and repository concepts. From this general catalogue, possible specific events are identified for each individual investigation area, and the necessary actions are derived. In addition to the demonstration of the basic possibility of safe operation, the robustness of operational safety within the investigation area is evaluated in a second step.

Nonsimilar modeling analysis of Carreau–Yasuda mixed convective flow in a porous medium subjected to Soret and Dufour influences

AbstractThis nonsimilar convection study is about the flow of Carreau–Yasuda (CY) nanofluid model above a vertically extendible surface. Convection in a fluid‐filled permeable medium has given due consideration because of its relevance in a variety of applications, including insulation, relocation of water from geothermal reservoirs, storage of nuclear waste, renewable energy, mechanical engineering, and enhanced oil reservoir recovery. By virtue of linear stretching and buoyancy effects, flow in a stationary fluid is induced along a vertical porous surface. In x‐momentum equation, linear buoyancy in the context of temperature and concentration is taken into consideration. Modeling of energy expression is done in the presence of Dufour and Soret influences. Governing differential system describing convection equations is changed into nonlinear partial differential system (PDE) by implementing applicable nonsimilar transformations. By making use of analytical local nonsimilarity (LNS) technique and bvp4c (numerical finite difference‐based algorithm), the transformed dimensionless nonsimilar structure is simulated numerically. At the end, the alteration of important nondimensional numbers is studied on transport quantities such as temperature, concentration and velocity field. The repercussions of relevant parameters on drag coefficient, Nusselt number and Sherwood number have been tabulated. Numerical simulations of nonsimilar model suggests that the velocity profile reduces due to rise in the values of Weissenberg number, porosity and suction parameter. The temperature profile is increased in comparison with the higher estimates, Eckert, and Dufour numbers. Because of larger values of Soret and Prandtl number, an increase in concentration profile is seen. Friction coefficient and Nusselt number increases with respect to higher estimations of porosity parameter, Weissenberg number and Prandtl number respectively, whereas they decrease against Dufour and Eckert variations.

Assessing energy balance via seismic and mechanical observations in high temperature induced crack damage in marbles

Assessing the rock physical and mechanical behavior under different temperatures has become of utmost importance. It is well known that thermal stresses induce significant crack damage in rocks due to thermal expansion or phase transformation and volume changes. Quantifying and forecasting the evolution of rock physical and mechanical parameters with temperature is thus crucial for evaluating rock integrity in many applications such as geothermal fields, nuclear waste storage, wildfire or volcanic processes. In marbles the degree of previous exposure to temperature and the chemical composition (i.e. calcite vs dolomite) plays a key role for controlling the mechanical evolution under temperature. Moreover separating out the energy contribution provided by anelastic processes driving crack damage and elastic reversible deformation under increasing temperature remains an open challenge. With these aims, three sample sets of marbles with different contents of calcite and dolomite from two Brazilian quarries were tested under different temperature conditions (from room temperature up to 600 °C). A marked increase of thermal cracking was observed after 400 °C, accompanying mass loss up to 1% and porosity increase. Moreover, a significant drop in seismic wave velocities, uniaxial compressive strength and electrical resistivity, in wet conditions, was also detected.Spectral behavior from seismic traces and energy dissipation from stress-strain curves were analyzed. A dominance of the dissipated energy compared to the elastic one was observed and related to the generation of new fracturing surfaces. This hypothesis was supported by the spectral behavior showing multiple scattering effects in the high frequency components, with an increase in attenuation. The results suggested that the percentage of dolomite has a high influence on the mechanical behavior even at low temperature, mirroring the prevalence of brittle processes in dolomitic marbles. This study represents a comprehensive benchmark for the study of effect of temperature on rocks because of its multidisciplinary and multimethod approach and the demonstrated sensitivity to subtle textural changes. Moreover, it provides a reliable tool for crack damage analysis at each thermal stress.

Evaluation of microbiologically influenced corrosion and biofouling in a nuclear storage basin

Biofouling and microbiologically influenced corrosion are major concerns to the long-term integrity of nuclear waste storage basins. The results of long-term microbial monitoring of nuclear storage at the Savannah River Site L-Basin nuclear material storage facility were examined to determine corrosion potential and biofouling. The densities of specific microbial species that can impact microbial corrosion and biofouling, including sulfate-reducing bacteria (SRB) and acid-producing (e.g., iron-oxidizing) bacteria (APB), were quantified by colony forming units (CFU). Several trends in microbial activity were observed during this time period. Overall microbial densities decreased slightly between 2000 and 2012. Metabolic diversity of microorganisms as measured by BIOLOG™ also decreased dramatically during this time. Aerobic microbial densities decreased from 2001 to 2010. Aerobes were most prevalent at 3.23 average CFU/mL and APB densities were lower at 0.80 average CFU/mL. From 2017 to present, iron-reducing bacteria were most prevalent at 3.41 average CFU/mL and APB were least prevalent at 0.44 average CFU/mL. All bacterial densities decreased except that of low-nutrient bacteria, which averaged 2.90 CFU/mL, and SRB averaged 0.19 CFU/mL. No distinct correlations between microbial concentrations, temperature, and either water chemistry parameters (pH and conductivity) or radiological conditions (19–30 disintegrations per minute (DPM) beta-gamma/mL; the equivalent to 0.32–0.50 Bq per mL) were determined. The occurrence of microbial biofilm formation on storage cannisters created biofouling issues in recent years. Although cleaning the biofouled surfaces provided temporary relief, the biofouling returned. Based on these results and physical observations of coupons, there has been minimal evidence of corrosion to date.

Model of water transfer in concrete and rock based on a single state variable to consider simultaneous positive pressure and drying boundary conditions

During their service life, concrete structures may be subjected to positive pressure and drying boundary conditions simultaneously. This phenomenon is likely to occur in civil engineering structures, such as tunnels for nuclear waste storage, dams, and piles, where the simultaneous phenomena of drying and saturation must be considered because of their strong effects on the short- and long-term behavior of the structure. The water transport model proposed in this paper predicts the mass transfer and water field in the material. It provides a continuous description of saturated and unsaturated media using liquid pressure as the only state variable and also considers the effects of temperature variations. A formulation for water transfer with a single state variable is presented, followed by an illustration of its numerical implementation and a procedure for the calibration of parameters. The model is compared with experimental and numerical results to validate its efficiency. For this purpose, several applications dealing with drying and saturation phenomena are used. The results obtained show the potential of the proposed water transfer model to evaluate the water transport in the material under study at different temperatures by simulating a mock-up of nuclear power plant wall. It is finally used to predict the re-saturation of an underground nuclear waste disposal structure.

Electronic Structure and Mechanical Properties of Solvated Montmorillonite Clay Using Large-Scale DFT Method

Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exothermic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of structural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio density functional theory. The DFT calculation and analysis clarify the important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk modulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at −8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay.

The temporality of community sentiment on the Australian continent: mineral extraction, waste storage and Indigenous protest writing

ABSTRACT The Australian federal government has recently recommenced a previously paused process to select a site for a national nuclear waste storage facility despite significant opposition from Australian Indigenous communities and others. This article considers what some might understand as a contemporary issue by examining its relationship to previous events. It emphasizes how Western linear temporality facilitates disregard for negative community sentiment and the consigning of previous wrongs to the past. In contrast, Indigenous temporalities – where time is understood as immanent and space and time intermingled – emphasize positive relationships and require the remediation of past wrongs to support just futures. Thus, historical nuclear weapons testing in Australia, current plans for waste storage, and historical and ongoing ecological and social consequences of resource extraction are all related, reflecting the violence of British colonization and contemporary settler colonial governance. Using a literary studies approach, this article examines historically significant moments of Indigenous Australian protest writing regarding extractive industries, nuclear waste storage, and settler colonial governance, to show that some Indigenous communities in Australia have clearly communicated their negative sentiments. It argues for equitable relationships as a first step towards the restitution of past wrongs and the creation of just futures.

Thermo-Osmosis in Charged Nanochannels: Effects of Surface Charge and Ionic Strength.

Thermo-osmosis refers to fluid migration due to the temperature gradient. The mechanistic understanding of thermo-osmosis in charged nano-porous media is still incomplete, while it is important for several environmental and energy applications, such as low-grade waste heat recovery, wastewater recovery, fuel cells, and nuclear waste storage. This paper presents results from a series of molecular dynamics simulations of thermo-osmosis in charged silica nanochannels that advance the understanding of the phenomenon. Simulations with pure water and water with dissolved NaCl are considered. First, the effect of surface charge on the sign and magnitude of the thermo-osmotic coefficient is quantified. This effect was found to be mainly linked to the structural modifications of an aqueous electrical double layer (EDL) caused by the nanoconfinement and surface charges. In addition, the results illustrate that the surface charges reduce the self-diffusivity and thermo-osmosis of interfacial liquid. The thermo-osmosis was found to change direction when the surface charge density exceeds -0.03C · m-2. It was found that the thermo-osmotic flow and self-diffusivity increase with the concentration of NaCl. The fluxes of solvent and solute are decoupled by considering the Ludwig-Soret effect of NaCl ions to identify the main mechanisms controlling the behavior. In addition to the advance in microscopic quantification and mechanistic understanding of thermo-osmosis, the work provides approaches to investigate a broader category of coupled heat and mass transfer problems in nanoscale space.