| 1. |
- Finsterle, S., et al.
(författare)
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Conceptual uncertainties in modelling the interaction between engineered and natural barriers of nuclear waste repositories in crystalline rocks
- 2019
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Ingår i: Geological Society Special Publication. - 0305-8719. ; 482:1, s. 261-283
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear waste disposal in geological formations relies on a multi-barrier concept that includes engineered components – which, in many cases, include a bentonite buffer surrounding waste packages – and the host rock. Contrasts in materials, together with gradients across the interface between the engineered and natural barriers, lead to complex interactions between these two subsystems. Numerical modelling, combined with monitoring and testing data, can be used to improve our overall understanding of rock–bentonite interactions and to predict the performance of this coupled system. Although established methods exist to examine the prediction uncertainties due to uncertainties in the input parameters, the impact of conceptual model decisions on the quantitative and qualitative modelling results is more difficult to assess. A Swedish Nuclear Fuel and Waste Management Company Task Force project facilitated such an assessment. In this project, 11 teams used different conceptualizations and modelling tools to analyse the Bentonite Rock Interaction Experiment (BRIE) conducted at the Äspö Hard Rock Laboratory in Sweden. The exercise showed that prior system understanding along with the features implemented in the available simulators affect the processes included in the conceptual model. For some of these features, sufficient characterization data are available to obtain defensible results and interpretations, whereas others are less supported. The exercise also helped to identify the conceptual uncertainties that led to different assessments of the relative importance of the engineered and natural barrier subsystems. The range of predicted bentonite wetting times encompassed by the ensemble results were considerably larger than the ranges derived from individual models. This is a consequence of conceptual uncertainties, demonstrating the relevance of using a multi-model approach involving alternative conceptualizations.
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| 2. |
- Soler, J. M., et al.
(författare)
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Predictive Modeling of a Simple Field Matrix Diffusion Experiment Addressing Radionuclide Transport in Fractured Rock. Is It So Straightforward?
- 2022
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 208:6, s. 1059-1073
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Tidskriftsartikel (refereegranskat)abstract
- The SKB GroundWater Flow and Transport of Solutes Task Force is an international forum in the area of conceptual and numerical modeling of groundwater flow and solute transport in fractured rocks relevant for the deep geological disposal of radioactive waste. Two in situ matrix diffusion experiments in crystalline rock (gneiss) were performed at POSIVA’s ONKALO underground facility in Finland. Synthetic groundwater containing several conservative and sorbing radiotracers was injected at one end of a borehole interval and flowed along a thin annulus toward the opposite end. Several teams performed predictive modeling of the tracer breakthrough curves using “conventional” modeling approaches (constant diffusion and sorption in the rock, no or minimum rock heterogeneity). Supporting information, derived from small-scale laboratory experiments, was provided. The teams were free to implement different concepts, use different codes, and apply the transport and retention parameters that they considered to be most suited (i.e., not a benchmark exercise). The main goal was the comparison of the different sets of results and the analysis of the possible differences for this relatively simple experimental setup with a well-defined geometry. Even though the experiment was designed to study matrix diffusion, the calculated peaks of the breakthrough curves were very sensitive to the assumed magnitude of dispersion in the borehole annulus. However, given the very different timescales for advection and matrix diffusion, the tails of the curves provided information concerning diffusion and retention in the rock matrix regardless of the magnitude of dispersion. In addition, although the task was designed to be a blind modeling exercise, the model results have also been compared to the measured experimental breakthroughs. Experimental results tend to show relatively small activities, wide breakthroughs, and early first arrivals, which are somewhat similar to model results using large dispersivity values.
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| 3. |
- Ericsson, Lars O, 1949, et al.
(författare)
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Comparison between blasting and wire sawing regarding hydraulic properties of the excavated damaged zone in a Tunnel – Experiences from crystalline rock at the Äspö hard rock laboratory, Sweden
- 2018
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Ingår i: 52nd U.S. Rock Mechanics/Geomechanics Symposium.
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Konferensbidrag (refereegranskat)abstract
- In tunneling with blasting, the tunnel periphery could be damaged (the EDZ, "Excavated Damaged Zone") with altered mechanical, hydraulic properties and reoriented stresses. In recent underground infrastructure projects, diamond wire cutting is used as an alternative excavation method. At the Äspö Hard Rock Laboratory in Sweden investigations have been conducted to determine hydraulic properties of the EDZ at water saturated conditions. Comprehensive hydraulic testing (hundreds of injection tests), in the floor of a blasted as well as a wire sawn tunnel section has made it possible to quantitatively compare hydraulic properties of the different excavation methods. Diamond wire cutting, as expected, greatly reduces the EDZ permeability compared to blasting.
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