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[en] Geological disposal of radioactive waste may give rise to gas injection into the host rock. The processes involved are subject of current research. In this study, the recently developed modelling tool TFC of GRS is used to model a number of coupled hydromechanical processes which may play a role in this scenario by means of a stylised gas injection experiment in rock salt. The simulation includes the gas emission phase, starting at the time of drilling the borehole, and the actual gas injection phase of the experiment. Rock salt is modelled as porous medium. Dependencies of hydrodynamic (H) parameters on mechanical (M) state changes (M→H-coupling) and of mechanical parameters on hydrodynamic state changes (H→M-coupling) are modelled by a number coupling functions. As to M→H-coupling, direct dependency of permeability on minimum effective stress is assumed as well as, alternatively, a poroelastic stress-porosity relationship with subsequent porosity-permeability relationship. As to H→M-coupling, independency between total stress and pore pressure is assumed as well as, alternatively, a poroelastic pore pressure vs. total stress relationship. Assuming direct dependency of permeability on effective stress, the simulations show that near the contour a permeability minimum develops in the emission phase, which does not vanish in the injection phase and which yields a very low gas flow. Assuming a mere poroelastic HM-coupling, gas emission is exceptionally low and also during the injection phase no enhanced gas injection can be achieved with this type of coupling. Apparently, pore volume changes in the framework of Biot's theory of poroelasticity are too small to result in such an effect. None of the various modelling assumptions results in a sudden injection of an actually large amount of gas. However, some simulations reveal an unexpected range of the injection front. Furthermore, a simulation with reduced bore hole diameter proves a scale dependency of effects of the contour, indicating a limited transferability of results from small scale experiments to repository scale conditions.
[en] The uncertainty and sensitivity of spent fuel degradation models on the release of radionuclides is studied by GRS and IRSN in the following report. An important part is to correlate the uncertainties in the assumptions made for simulating the spent fuel degradation and the uncertainties in the associated release of radionuclides and to determine the sensitivity of the parameters by a probabilistic method. Sensitivity analysis was performed already using deterministic calculations in the french case /AND 05/. GRS and IRSN have decided to model the concept based on the ANDRA's Carbon steel SF/Iron/Clay concept /NF 05/ as a test case. Spent fuel canisters are disposed of in horizontal tunnels closed by a bentonite plug. A bentonite buffer is placed around the canisters. Bentonite seals close the access drifts in order to limit the water flow in the repository. GRS/IRSN decided to use I-129 as an example for the release and transport.
[en] Uncertainty and sensitivity analyses for hydraulic single-phase models have long been the state of the art and have been employed in safety cases for the disposal of radioac-tive waste. We present uncertainty and sensitivity analyses of selected parameters for two-phase fluid flow calculations of a full scale repository system. Computing time for these calculations was acceptable, so that in the future, further and more comprehen-sive analyses will be feasible. One hundred model runs yielded one hundred time series for a radiological indicator. Overall, 10 independent and dependent parameters were varied. The time series are characterized by two distinct peaks occurring very early and relatively late during the modelled time of 10,000 years. Using uncertainty analysis it was possible to formulate a statement regarding what frac-tion of the result's probability distribution falls below the critical limit of our chosen ra-diological indicator (with a given confidence level). With a confidence level of 99 % this is the case for at least 90 % of the probability distribution of the calculated results. The sensitivity analysis of the repository system shows that - given the chosen proba-bility distributions of the input parameters - the compaction times of salt grit in em-placement fields and in main drifts are the determinants for the height of the early peak and that final porosity is the by far most important determinant for the height of the second peak. The time-indexed sensitivity analysis of the radiological indicator pro-vides insight into the repository system's behaviour and strengthens the confidence in the robustness of the correlated parameters' analysis.
[en] Most, if not all, national programs for radioactive waste management (RWM) pledge their overall commitment to safety or - in the case of radioactive waste disposal - to long-term safety. Therefore, it may be somewhat surprising to find that the term 'safety' is hardly defined in these programs. The same holds for some of the core international guidance literature on the deep geological repository (DGR) 'safety case' concept. With respect to stakeholder concern over the safety of geological disposal, it seems, however, advisable to seek common ground in the understanding of the idea of 'safety'. In this paper, we review and discuss the most relevant international guidance literature's provision (or non-provision) of definitions of 'safety' in the context of radioactive waste disposal. Against this background, we develop a tentative, practical, glossary-style definition of 'safety' in the DGR context. As a seed of discussion, it may help to eventually expose possible mismatches in the base assumptions of safety experts and other stakeholders. (authors)
[en] The present report documents verifications tests for the codes TOUGH2-GRS, version 2, and TOUGH2-MP-GRS, version 0. Code tests have been conducted using the code SITA, a tool for automated code testing.
[en] The medium term was introduced as the period of indirect oversight after repository closure, with timescales in the order of a few hundred years. While the importance of intrinsic control or 'passive' safety features in the post-closure phase of a geological repository has been recognised and stressed before, the role of oversight, by providing the capability to reduce or avoid some exposures, has come to the fore only recently. Oversight for the time being generally refers to 'watchful care' and society 'keeping an eye' on the technical system and the actual implementation of plans and decisions. In some regulatory frameworks oversight is indirectly required, for instance when mandating the creation of a land exclusion zone. In other frameworks, oversight is directly required, as illustrated, for instance, by the long-term stewardship concept of the US Environmental Protection Agency. Although sheer memory of the presence of the facility cannot be enough to constitute oversight, oversight and RK and M preservation do go hand in hand. For example, monitoring after repository closure fosters RK and M preservation, and vice versa. The presenter focused on terminology, potential oversight measures, and on roles and responsibilities of different stakeholders
[en] The report on developments and studies on the (T)HMC (thermal-hydraulic-mechanical-chemical) processes in a final repository for heat generating radioactive wastes covers the following topics: description of the projects, applied codes: TOUGH2, FLAC3D, TOUGH2 and FLAC3D, TOUHREACT/PetraSim, MARNIE, PHREEQC, geochemists workbench, SUSA; safety relevant singular processes in the transition phase, uncertainties due to process interactions, coupling of mass transport and geochemical equilibria, further developments and application of numerical simulations in the transition phase.
[en] Project 4715E03230 ''Bewertung der Methoden zur Durchfuehrung und Analyse der Betriebs- und Langzeitsicherheitsnachweise von Endlagern'' of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) is devoted to methods and codes for the assessment of the operational and post-operational safety of deep geological repositories for radioactive waste. The investigation focusses on saliniferous and argillaceous host rock as well as on repository systems with variable groundwater density. Flow and transport codes of GRS as well as pre- and postprocessing tools have been extended to render possible or improve the simulation of relevant processes in repository systems. The methodology of accident analyses for the operational phase has been further developed based on the scenario development for the post-operational phase.
[en] Concepts for the use of markers in the post-closure phase of deep geological repositories (DGRs), are often designed to prevent 'inadvertent' human intrusion (HI), while it is common practice not to protect against deliberate intrusion (i.e. 'advertent' HI). In the literature, inadvertent HI prevention studies usually combine future human activity scenarios with the assumption that all memory of the DGR has been lost, and analyze what can be done now to make the possible future intruder 'aware' of the associated risks. In this paper, we show that the classical 'advertent'/'inadvertent' duality classification of HI, as used in the performance assessment context, is not ideal to characterize potential HI situations in the RK and M preservation context. We suggest that the relevant HI categories are expanded and refined to 'un/necessary HI', 'un/intentional HI' and 'un/friendly HI'. Along with refining the taxonomy of HI that way, we refine the assumption relating to the loss of memory of the DGR. Different HI situations are likely to arise in different 'loss-of-memory situations'. We analyze the resulting 5 classes of the proposed HI classification and find that 2 hold the classic 'advertent' and 'inadvertent' HI scenarios while 3 are 'new'. We apply the proposed categories to sub-surface marking concepts from the literature and suggest that, in particular, sub-surface marking concepts would benefit from this new approach to HI and loss-of-memory categorization. (authors)
[en] The research and development project "Derivation of scenarios for the long-term phase of repository systems in different host rocks as well as integrity verification for the host rocks clay and crystalline1" (funding reference 4716E03230, duration: November 2016 to August 2019) deals with individual aspects of the safety verification for the repositories of radioactive waste in deep geological formations. The Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH follows the international state of science and technology on the following topics and develops it further: - Integrity criteria for the host rock clay rock, - Integrity criteria for the host rock crystalline rock, - Modelling and code development for the coupling of thermo-hydro-mechanical (THM) processes and - Further development of methods for the derivation of scenarios for repository systems in different host rocks. The project is funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). This report describes the motivation and tasks of the respective working points (Section 1.1). The literature published in the project is given in Section 1.2. The work carried out and the results achieved are summarised in Chapter 2. Finally, an outlook on the use of the results of this project and open research and development work is given (Chapter 3).
[de]Das Forschungs- und Entwicklungsvorhaben „Ableitung von Szenarien für die Langzeitphase von Endlagersystemen in verschiedenen Wirtsgesteinen sowie Integritätsnachweis für die Wirtsgesteine Ton und Kristallin1“ (Förderkennzeichen 4716E03230, Laufzeit: November 2016 bis August 2019) beschäftigt sich mit Einzelaspekten der Sicherheitsnachweise für die Endlager radioaktiver Abfälle in tiefen geologischen Formationen. Die Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH verfolgt dabei den internationalen Stand von Wissenschaft und Technik zu folgenden Themen und entwickelt ihn dabei weiter: - Integritätskriterien für das Wirtsgestein Tongestein, - Integritätskriterien für das Wirtsgestein Kristallingestein, - Modellierungen und Codeentwicklung zur Kopplung von thermo-hydro-mechanischen (THM) Prozessen und - Weiterentwicklung von Methoden zur Ableitung von Szenarien für Endlagersysteme in verschiedenen Wirtsgesteinen. Zuwendungsgeber des Vorhabens ist das Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit (BMU). Der vorliegende Bericht beschreibt die Motivation sowie Aufgabenstellung der jeweiligen Arbeitspunkten (Kap. 1.1). Die im Vorhaben veröffentlichte Literatur ist in Kap. 1.2 angegeben. Die durchgeführten Arbeiten und daraus erzielte Ergebnisse sind in Kap. 2 zusammengefasst. Abschließend wird ein Ausblick zur Verwendung der Ergebnisse dieses Vorhabens und offene Forschungs- und Entwicklungsarbeiten gegeben (Kap. 3).