Pumping, tracer and dilution tests on a site scale (1 km).
As the first task, a large scale field experiment was chosen. This consisted of a long term pumping test, dilution tests as well as a series of tracer tests. The modelling work performed during 1992-1994 has been evaluated by the Task Force group. The experiences are discussed from the modelling point of view, the Äspö data collection point of view and the site characterisation point of view.
This task is completed.
The modelling work performed during 1994-1996 has been evaluated by the SKB Task Force group. The experiences are discussed from the modelling point of view, the Äspö data collection point of view and the site characterisation point of view.
Seven different groups modelled Task No 3 using different conceptual and numerical methodologies for simulating flow in fractured rocks. The modelling work has been reported within the Äspö ICR Series.
This task is completed.
Radially converging tracer tests as well as dipole tests, detailed scale (1-10m).
Task 4 consists of modelling exercises in support of the TRUE tracer tests. Predictive modelling is also performed where the experimental results are not available beforehand.
|4A||Modelling in support of the development of a descriptive structural model of the test site|
|4B||Modelling in support of experimental design|
|4C||Predictive modelling of the radially converging tracer tests in the feature. Comparison of model output with experimental results.|
|4D||Predictive modelling of the dipole tests in the feature. Comparison of model output with experimental results. Evaluate what can be achieved with existing data set of TRUE-1 in terms of transport predictions for non-sorbing tracers.|
|4E||Predictive modelling of the TRUE-1 tracer tests with sorbing tracers. Comparison of model output with experimental results.|
|4F||Evaluation of what can be achieved with existing in-situ and laboratory data from the TRUE-1 site in terms of predicting transport of solutes subject to sorption.|
The task is completed.
Task 5 commenced in 1998 and was finalised in 2002. Participating modelling teams in the project represented ANDRA (France; three modelling teams – ANTEA, ITASCA, CEA), BMWi/BGR (Germany), ENRESA (Spain), JNC (Japan), CRIEPI (Japan), Posiva (Finland) and SKB (Sweden; two modelling teams – CFE and Intera (now GeoPoint)).
Experience from Task 5 has highlighted several important aspects for site investigations facilitating the possibilities for mathematically integrated modelling and consistency checks that should be taken into account for future repository performance assessments.
Equally important is that Task 5 has provided the opportunity to bring together two scientific disciplines which have traditionally tended to work in parallel rather in collaboration. This is an important first step. There is now a much stronger appreciation that the use of hydrogeochemistry can lead to an increased understanding of hydrogeology and vice-versa.
Solute transport is a key aspect of both Performance Assessment (PA) and repository Site Characterisation (SC). Task 6 seeks to provide a bridge between SC and PA approaches to solute transport in fractured rock and focuses on the 50 to 100m scale. Task 6 tries to bridge the gap between PA and SC models by applying both approaches for SC boundary conditions (i.e. for trace experiments), and also for PA boundary conditions.
The objectives of Task 6 are:
- Assess simplifications used in PA models
- Assess the constraining power of tracer (and flow) experiments for PA models
- Provide input for SC programs from a PA perspective
- Understand the site-specific flow and transport behaviour at scales using SC models.
The task is completed
The contents of the model assignments within Task 6 are summarised in the table below.
|6A||Model and reproduce selected True-1 tests with a PA model and/or a SC model to provide a common reference.|
|6B||Model selected PA cases at the True-1 site with new PA relevant (long term/base case) boundary conditions and temporal scales. This task serves as means to understand the differences between the use of SC-type and PA-type models, and the influence of various assumptions made for PA calculations for extrapolation in time.|
|6C||Develop semi-synthetic, fractured granite hydrostructural models. Two scales are supported (200 m block scale and 2000 m site-scale). The models are developed based on data from the Prototype Repository, True Block Scale, True-1, and Fracture Characterisation and Classification project (FCC).|
|6D||This sub-task is similar to sub-task 6A, and is using the synthetic structural model in addition to a 50 to 100 m scale True-Block Scale tracer experiment.|
|6E||This sub-task extends the sub-task 6D transport calculations to a reference set of PA time scales and boundary conditions.|
|6F||Task 6F is a sensitivity study, which is proposed to address simple test cases, individual tasks to explore processes, and to test model functionality.|
Task 7 concerns modelling of a long-term pumping experiment at the Olkiluoto site in Finland. The task lies within a broader setting of site investigations, site characterisations, and ultimately safety assessment issues. The focus is especially on increased understanding of the major fracture zones behaviour as boundaries for bedrock compartments and the interaction between these “isolated” compartments and the major flow system. The experiences are supposed to provide a bridge between site characterisation and safety assessments.
An interaction between engineered and natural barriers
- Deposition boreholes in their tunnel environment
- Assessment of feasible deposition boreholes
- The hydraulic interaction between the rock and water unsaturated bentonite in a deposition borehole
- The effects of re-saturation on the flow system
- The understanding of post-resaturation flow and transport
Bentonite Rock Interaction Experiment (BRIE) In order to give data to the modelling a supporting field experiment at Äspö Hard Rock Laboratory is being planned (BRIE). In the experiment a borehole will be filled with unsaturated bentonite. The borehole will be drilled in a part of the rock containing both few fractures with different transmissivity and a part of rock with no fractures. Total stress, pore water pressure and RH will be measured in the bentonite. In the rock pore water pressure and RH will be measured close to the rock wall if possible. After suitable time the hole will be over-cored and the bentonite analysed mainly regarding water content distribution. In the experiment new technologies are required to:
- characterize the hydraulic conductivity of the rock for extremely low levels
- characterize the dual porosity/dual permeability system
- monitor stress and water saturation in detail
- characterize the stress/pressure/permeability coupling
The modelling task will be to model the evolution in space and time of:
- the rock: the water pressure and water flow in the rock matrix and fractures around a deposition borehole
- the bentonite: the water pressure, total pressure (swelling pressure), density and water content in a deposition borehole
- the interface: Exchange of water over the interface between the bentonite and a sparsely fractured rock. The interface as a mutual boundary condition.
Task 9 focused on modelling of coupled matrix diffusion and sorption in heterogeneous crystalline rock matrix at depth. This was done in the context of inverse and predictive modelling of tracer concentrations of the in-situ experiments performed within LTDE-SD at the Äspö Hard Rock Laboratory in Sweden, and the REPRO project at the ONKALO underground rock characterisation facility in Finland, focusing on sorption and diffusion. The ultimate aim was to develop models that in a more realistic way represent retardation in the natural rock matrix at depth.
The topic of radionuclide transport and retardation in the geosphere is of high importance for assessing the safety of geological repositories for radioactive waste in fractured crystalline rock. Matrix diffusion of solutes in the microporous system of the rock matrix is perceived to be well understood and has been discussed for over 60 years. For the past 35 years, matrix diffusion coupled with sorption has been discussed in the context of retardation of radionuclides potentially migrating from a geological repository for nuclear waste. In recent safety assessments, carried out by SKB and Posiva, the importance of solute exchange between flowing fracture water and stagnant pore water has been stressed in regard to the waste containers’ capability of isolating spent nuclear fuel over long time periods.
LTDE-SD was an in-situ study that was carried out at Äspö HRL and it focused on tracer transport in the stagnant pore water of the rock matrix. In the experiment, a cocktail of both sorbing and non-sorbing tracers was allowed to contact a natural fracture surface, as well as the unaltered rock matrix, for a time period of 200 days. The experiment was carried out at a depth of about 410 m below sea level.
The REPRO project was in part carried out in-situ in ONKALO at Olkiluoto in Finland, and in part as an extensive laboratory programme. Concerning in-situ experiments; two water phase diffusion and sorption campaigns were carried out from the REPRO niche at about 400 m depth, from which a number of drillholes has been drilled. These campaigns were the WPDE (Water Phase Diffusion Experiment) series of experiments and the TDE experiment (Through Diffusion Experiment). The in-situ part of REPRO aimed to tackle the topics of diffusion, sorption; anion exclusion; and rock matrix anisotropy. In addition, the laboratory part focused on small scale rock characterisation.
Modelling in Task 9
Task 9 was initiated in the spring of 2015 and started with semi-predictive modelling of the REPRO project. The second subtask focuses on the inverse modelling of experimental results from the in-situ tracer test LTDE-SD. In a following subtask the penetration profile of Cl-36, Cs-137 and Ni-63 into the LTDE-SD rock matrix will be modelled in a predictive fashion. In addition, the TDE (Through Diffusion Experiment) of REPRO was modelled as well.
As an optional subtask, the increased realism in the solute transport codes was put into the perspective of safety assessment time scales. This was to highlight if different aspects of matrix diffusion and sorption, utilising codes with increased complexity and realism, may have any consequence for long-term retardation.