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  • 1
    Online Resource
    Online Resource
    Copernicus GmbH ; 2023
    In:  Safety of Nuclear Waste Disposal Vol. 2 ( 2023-09-06), p. 103-103
    In: Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 2 ( 2023-09-06), p. 103-103
    Abstract: Abstract. The thermal, hydraulic, and mechanical effects of excavating the repository mine and the thermal loading of nuclear waste on the safety of the geological barrier system are addressed in the regulations as integrity analyses. For repositories in clay rock, a modelling and assessment methodology has been developed in the ANSICHT (Methodik und Anwendungsbezug eines Sicherheits- und Nachweiskonzeptes für ein HAW-Endlager im Tonstein) project based on thermo-hydro-mechanically (THM) coupled simulations using the open-source software project OpenGeoSys and has been illustrated by its application to a generic clay rock site in northern Germany. However, the assessment can be significantly influenced by uncertainties in the model inputs, which result, on the one hand, from the limited ability to characterize the geological barrier and, on the other hand, from fundamental difficulties and inaccuracies in the measurements. Hence, the results of these established integrity analyses have to be enriched by statistical information. The developed workflow comprises different steps beginning with a realistic characterization of parameter uncertainties. A surrogate model based on mathematically sound techniques is built to capture the propagation of these uncertainties through the THM simulation and the integrity criteria evaluation. The model can then be evaluated to obtain probabilistic results for rock integrity assessment and a sensitivity analysis to identify the inputs that primarily impact the results. In this contribution, we present preliminary results based on the generic repository system from the ANSICHT project and the developed tools for stochastic analyses. This work is done as part of the BGE-funded research cluster URS (Uncertainties and Robustness with regard to the Safety of a repository for high-level radioactive waste).
    Type of Medium: Online Resource
    ISSN: 2749-4802
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 2
    In: Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 2 ( 2023-09-06), p. 109-111
    Abstract: Abstract. For the underground disposal of high-level nuclear waste in rock salt formations, the safety concept includes the backfilling of open cavities with crushed salt. For the prognosis of the sealing function of the backfill for the safe containment of the radioactive waste, it is crucial to have a comprehensive process understanding of the crushed-salt compaction behavior. The crushed-salt compaction process is influenced by internal properties (e.g., grain size, mineralogy, and moisture content) and boundary conditions (e.g., temperature, stress state, and compaction rate) and, therefore, involves several coupled thermal–hydro–mechanical (THM) processes (Hansen et al., 2014; Kröhn et al., 2017). With the paradigm shift from the limited release of radionuclides to safe containment due to the German Repository Site Selection Act passed in 2017, the importance of crushed salt as geotechnical barrier has increased, with a focus on the evolution of its hydraulic properties. Based on the knowledge gaps in the current process understanding, the “Compaction of crushed salt for safe containment” (KOMPASS) projects were initiated to improve the scientific basis behind using crushed salt for the long-term isolation of high-level nuclear waste within rock salt repositories. The efforts to improve the prediction of crushed-salt compaction begun during the first phase of the KOMPASS projects (Czaikowski et al., 2020) and were followed up in a second phase ending in June 2023. The primary achievements of the projects are as follows (Czaikowski et al., 2020; Friedenberg et al., 2022): specification of the KOMPASS reference material, an easily available and reproducible synthetic crushed-salt material, for generic investigations; development of pre-compaction methods and successful production of samples in the short term and under in situ loading conditions; formulation of an extended laboratory program addressing the isolated investigation of known relevant factors influencing the compaction behavior of crushed salt (Düsterloh et al., 2022); execution of long-term compaction tests addressing isotropic and deviatoric load changes, temperature, and compaction state; construction of a backfill body using the KOMPASS reference material in the Sondershausen mine through collaboration with the SAVER (Entwicklung eines salzgrusbasierten Versatzkonzepts unter der Option Rückholbarkeit) project (Schaarschmidt and Friedenberg, 2022); advancement of the tools for microstructure investigation methods (Svensson and Laurich, 2022); generation (first stages) of a microphysical process list combining literature research with our own findings; benchmarking of long-term compaction test for model development and optimization of various existing models as well as the development of new models; application of a virtual demonstrator (2D model representing a backfilled drift in rock salt) for the visualization of developments and the quantification of the models (Rabbel, 2022). In summary, the KOMPASS projects contributed to the reduction of uncertainties and the strengthening of the safety case for using crushed salt within rock salt repositories.
    Type of Medium: Online Resource
    ISSN: 2749-4802
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 3
    In: Environmental Earth Sciences, Springer Science and Business Media LLC, Vol. 83, No. 2 ( 2024-01)
    Abstract: The Federal Company for Radioactive Waste Disposal (BGE mbH) is tasked with the selection of a site for a high-level radioactive waste repository in Germany in accordance with the Repository Site Selection Act. In September 2020, 90 areas with favorable geological conditions were identified as part of step 1 in phase 1 of the Site Selection Act. Representative preliminary safety analyses are to be carried out next  to support decisions on the question, which siting regions should undergo surface-based exploration. These safety analyses are supported by numerical simulations building on geoscientific and technical data. The models that are taken into account are associated with various sources of uncertainties. Addressing these uncertainties and the robustness of the decisions pertaining to sites and design choices is a central component of the site selection process. In that context, important research objectives are associated with the question of how uncertainty should be treated through the various data collection, modeling and decision-making processes of the site selection procedure, and how the robustness of the repository system should be improved. BGE, therefore, established an interdisciplinary research cluster to identify open questions and to address the gaps in knowledge in six complementary research projects. In this paper, we introduce the overall purpose and the five thematic groups that constitute this research cluster. We discuss the specific questions addressed as well as the proposed methodologies in the context of the challenges of the site selection process in Germany. Finally, some conclusions are drawn on the potential benefits of a large method-centered research cluster in terms of simulation data management.
    Type of Medium: Online Resource
    ISSN: 1866-6280 , 1866-6299
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2024
    detail.hit.zdb_id: 2493699-6
    SSG: 13
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  • 4
    In: Environmental Earth Sciences, Springer Science and Business Media LLC, Vol. 82, No. 13 ( 2023-07)
    Abstract: In this paper, thermo-hydro-mechanically (THM) coupled processes triggered during the construction, operation and closure of a deep geological repository for heat generating, high level radioactive waste are discussed based on a generic disposal concept. For this purpose, we are using the numerical non-isothermal two-phase–two-component flow in deformable porous media (TH 2 M) implementation (Grunwald et al. in Geomech Geophys Geo-energy Geo-resour, 2022) in the open-source software OpenGeoSys (Bilke et al. in Transport Porous Media 130(1):337–361, 2019, https://doi.org/10.1007/s11242-019-01310-1 ). THM coupled effects covered in this work focus on single and two-phase-flow phenomena, gas and heat generation as well as poro-elastic medium deformation. A suitable set of benchmarks covering aforementioned THM-effects, devised in the scope of the BenVaSim benchmarking project (Lux et al. in Synthesis report. BenVaSim—International Benchmarking for Verification and Validation of TH2M Simulators with Special Consideration of Fluid Dynamical Processes in Radioactive Waste Repository Systems. Tech. rep., 2021, https://doi.org/10.13140/RG.2.2.28998.34887 ) is chosen and one additional benchmark is presented, allowing for the demonstration and comparison of the OGS-6 TH 2 M implementation against results obtained by other well-established codes used in the field. Apart from the code comparison, the benchmarks also serve as means to analyze THM coupled processes in a repository based on very simplified geometries. Therefore, they can help to improve the process understanding, but any quantitative results should not be interpreted as predictions of the behaviour of a real repository. The results obtained in this work agree well with the results presented by the project partners in BenVaSim—both in single phasic, fully liquid saturated cases and in partially saturated two phase regions. Hence, the suitability of the OGS-6 TH 2 M implementation for the application in the field of radioactive waste management, supporting the safety case and analyzing the integrity of the geological and geotechnical barrier systems is demonstrated. Finally, a detailed discussion of observed phenomena in the benchmarks increases our understanding and confidence in the prediction of the behaviour of TH 2 M coupled systems in the context of deep geological radioactive waste disposal.
    Type of Medium: Online Resource
    ISSN: 1866-6280 , 1866-6299
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2493699-6
    SSG: 13
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  • 5
    In: International Journal of Rock Mechanics and Mining Sciences, Elsevier BV, Vol. 170 ( 2023-10), p. 105534-
    Type of Medium: Online Resource
    ISSN: 1365-1609
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2023
    detail.hit.zdb_id: 2016557-2
    SSG: 19,1
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  • 6
    In: Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 2 ( 2023-09-06), p. 93-94
    Abstract: Abstract. The simulation of thermal, hydraulic, and mechanical coupled processes can be a decisive factor in the integrity assessment of geotechnical and geological barriers. Modelling decisions, such as the representation of heterogeneity and the constitutive models used, significantly impact the simulation outcome (Wagener and Pianosi, 2019). Furthermore, numerical inputs to the simulation, i.e. material parameters and boundary conditions, are subject to uncertainty. This results in a lower confidence level of the outcome, even if the overall simulation framework is well validated. To derive robust conclusions from such analyses, it is important to quantify the relative impact of modelling decisions and inputs on certain quantities of interest. Parameter uncertainties can be quantified by their forward propagation through the discretized problem (Helton, 1994), providing a natural frame of reference for quantifying structural uncertainty (Bond et al., 2007), such as the representation of heterogeneity, and for model validation. This contribution will focus on the latter aspects. We present research on workflows for the unification of evaluating uncertainty in experimental data and certain modelling decisions. We first focus on parameter uncertainty quantification and the resulting conclusions concerning the chosen modelling approach. Hereafter, scale questions are addressed in the context of heterogeneity and anisotropy, based on selected case studies. We close by discussing two example applications, namely one at the Underground Research Laboratory (URL) scale (Mount Terri Full-Scale Emplacement (FE) experiment) and one at the repository scale (ANSICHT Ton Nord model). This work is done as part of the Bundesministerium für Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz (BGE URS) research cluster.
    Type of Medium: Online Resource
    ISSN: 2749-4802
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 7
    Online Resource
    Online Resource
    Copernicus GmbH ; 2023
    In:  Safety of Nuclear Waste Disposal Vol. 2 ( 2023-09-06), p. 115-115
    In: Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 2 ( 2023-09-06), p. 115-115
    Abstract: Abstract. Since a sufficiently large undisturbed rock zone to provide the essential safety function for containment of radioactive waste cannot be assumed in crystalline rock, a concept for disposal in multiple smaller unfractured rock volumes has been developed and investigated in the joint research project CHRISTA-II (Thiedau et al., 2021). This repository concept, which relies on the host rock as an essential barrier for the containment of the disposed radionuclides, thus requires the existence of sufficiently large unfractured areas. Integrity evaluation of the geological barrier as part of the safety assessment comprises a safety-oriented assessment of mechanical, hydraulic, thermal and chemical processes occurring in the host rock as well as their couplings. Fractures and other types of discontinuities, which usually characterize crystalline rock, are expected to influence the hydraulic behavior of the system. Therefore, representing adequately the fracture network is necessary in order to capture its relevant properties, which will ultimately define the hydraulic boundary conditions surrounding the unfractured containment rock zones. Typically it is only possible to characterize fracture networks statistically, which requires a systematic investigation to quantify the influence of multiple realizations on a repository system. Moreover, the estimation of the potentially available undisturbed rock zone volume, making use of an ensemble of statically equivalent fracture networks, is relevant for the repository concept presented here. This contribution aims to further develop the methodology for integrity assessment presented in Thiedau et al. (2021) with a focus on the influence of the uncertain fracture distribution.
    Type of Medium: Online Resource
    ISSN: 2749-4802
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 8
    In: Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 1 ( 2021-11-10), p. 173-174
    Abstract: Abstract. The disposal of heat-generating nuclear waste in deep geological formations is an internationally accepted concept. Several repository systems are under discussion in Germany, whereby claystone, salt or crystalline rock could act as the host rock. In this contribution we focus on repository systems where the Containment Providing Rock Zone (CRZ) ensures safe enclosure of the waste and thus the geologic barrier is essential. Even though the various rock types considered differ substantially in their mechanical, hydraulic, thermal and chemical behavior, they must all meet the same safety requirements as defined by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) in 2020. As part of these safety requirements, it must be shown that the integrity of the CRZ is guaranteed for the verification period, i.e. the retention of the properties essential for the containment capacities must be demonstrated over 1 million years. Therefore, the formation of new pathways must be avoided and temperature development must not significantly impair the barrier effect. The anticipated stresses and fluid pressures should not exceed the dilatancy strength and the fluid pressure capacity, respectively. In order to assess the compliance of these requirements, numerical modelling is an essential and powerful tool. Even though great progress has been made regarding the efficiency of computational methods, multiphysical modelling on different length scales over long time periods is still a challenging task. Moreover, since readily available solutions do not exist, adapted methods have to be developed and evaluated, in order to verify concepts and numerical implementations. The BGR gained experience in the field of thermal, hydraulic, mechanical (THM) numerical analysis of the integrity of the CRZ in salt rock and clay stone joined research projects on German disposal options. For crystalline rocks, first concepts are currently being developed within the CHRISTA II project. Compared to clay stone and salt rock, special features have to be taken into account: First of all, crystalline rock is characterized by fractures and other discontinuities. Thus, it cannot be assumed that an undisturbed area of sufficient size can be found for the entire nuclear waste. Consequently, several smaller CRZs must be defined, each providing undisturbed rock. Numerical analysis must deal with smaller CRZs and mechanical and hydraulic boundary conditions that are influenced by fractures. In addition, the processes in the individual CRZs may influence each other (e.g. Temperature distribution). Preliminary modelling approaches and results of numerical THM analyses, considering an upscaled fracture network, are presented.
    Type of Medium: Online Resource
    ISSN: 2749-4802
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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