Kickmaier W., Birkhäuser Ph., Gautschi, A., Thury M.
Nagra, Wettingen, Switzerland

Two underground research facilities are currently operational in Switzerland – the Grimsel Test Site (GTS) in crystalline rock and Mont Terri in shale (Opalinus Clay). Although the host rocks are significantly different, these underground laboratories have many similarities – being located in mountainous regions, having horizontal access via existing tunnels to research areas with several hundred metres of overburden and being run with international collaboration.

The GTS has been in operation since 1983 and many of the projects carried out in this time have been completed and documented in the open literature. Highlights of Phase IV (1994-1996) include completion of the Radionuclide Retardation Project, studies of two-phase flow in the vicinity of the tunnel walls, seismic tomography tests and development of the technology for sealing horizontal boreholes. Phase IV also saw initiation of the Full-scale Engineered Barrier EXperiment (FEBEX), which will run until about 2001. The current Phase V (1997-2002) also includes further radiochemical studies (involving high pH fluids, colloids and determination of in-situ speciation) and gas migration tests.

The Mont Terri project was launched in 1996 and studies initially focused on development of characterisation methodology for the very low permeability Opalinus Clay. Construction of a new tunnel to allow study of excavation disturbance effects and examine the mechanical properties of this rock in further detail started in November 1997. Geochemical studies also feature prominently at Mont Terri.

Apart from the value of individual projects at these facilities, parallel studies allow cross comparisons to be made on particular properties of sedimentary and crystalline rocks. This is of particular value to countries like Switzerland, Japan, France and Spain, where various options for the HLW repository host rock are considered.

The paper will provide an overview of the current status of all projects ongoing at these two facilities and an outline of possible future developments at these sites.

The Swiss radioactive waste management concept foresees the disposal of radioactive waste in deep geological formations. A L/ILW repository is planned in a Cretaceous Marl formation at the Wellenberg Site in Central Switzerland. For a HLW repository, two host rock formations in Northern Switzerland are under consideration: the crystalline basement and the Opalinus Clay, a Jurassic shale / claystone formation. A major milestone of Nagra's programme is the general assessment of feasibility and safety for a HLW-repository: the so-called ''Entsorgungsnachweis''.

A key feature of Nagra's research and development work in the underground laboratories (URL) is in its direct relationship to repository programmes and within the near future specifically to the ''Entsorgungsnachweis'', however, the GTS was also established to support the L/ILW programme which is now focused on the WLB site. Nagra decided to begin underground research almost 15 years ago. Since 1983, Nagra has operated the Grimsel Test Site (GTS), a first generation URL in the crystalline rocks of the Central Aar Massif. Complementary to the ongoing Opalinus Clay programme in the Zürcher Weinland, Nagra is participating in the Mont Terri Project, which is operated under the patronage of the Swiss National Hydrological and Geological Survey since 1996. The location and schematic layout of the URLs are shown in Figures 1 and 2. A synthesis report, summarising the main conclusions of the URL-programmes, is planned by the year 2000.

On the basis of experience already gained in the URLs, a ''top – down planning strategy'' has been systematically applied to select recent research programmes. The basic input for the selection of experiments is the definition of key areas of interest, and specifically open questions related to the main milestones in the repository programmes, which are then translated into working programmes by the experimentalists. The integration of performance assessors and site characterisation groups in the planning and synthesis of results has been proven to increase the benefit obtained from experiments performed underground. In addition to the scientific and technical value of the URLs, the issue of public acceptance is becoming increasingly important. By supplying direct information to the public from (and in) a "realistic" environment, the feasibility of safe disposal can be illustrated and conveyed in a convincing manner.

The Grimsel Test Site (GTS) is located approximately 450 metres beneath the east flank of the Juchlistock mountain in the granitic rocks of the Aar Massif. The tunnel system of the GTS has a total length of around one kilometre and was excavated in 1983. Most of the excavation was done using a full-face tunnel boring machine (TBM) with a diameter of 3.5 metres. At this time, for the HLW repository, a tunnel system of this diameter was under consideration. For specific experiments, caverns were excavated by a conventional drill and blast technique. In 1995, a new TBM tunnel with a diameter of 2.3 m was drilled for the FEBEX-Experiment.

The conditions for performing experiments at the GTS are particularly favourable because it contains areas of relatively undisturbed low-permeability rock, as well as water-bearing zones (shear zones, fractures and lamprophyre dykes). In particular, the existence of a "radioprotected zone" (Type B), in which it is possible to carry-out experiments using radionuclides in-situ, extends the range of potential experiments at the GTS. The Migration Experiment (Frick, 1994), the Radionuclide Retardation Project (Alexander et al., 1997) and also the recently initiated experiments of GTS Phase V (1997-2002), are examples of this type of experiment.

Following four R&D phases, an extensive site-characterisation database for the planning, performance and interpretation of new experiments is available, in general decreasing the cost/benefit ratio. It should be noted that international cooperation always has been a key issue of the GTS Project.

Reviewing the objectives and results obtained since 1983, the main experimental phases can be seen as addressing the following three questions:

What is possible? – What is needed? – How can output be optimised?

The GTS-Project started with experiments focused on the demonstration of the basic feasibility of various aspects of site characterisation. The understanding of the site, and especially of the hydrogeological situation, achieved by a series of hydraulic experiments, in addition to a comprehensive geophysical programme and a detailed characterisation of water-conducting features, clarified further requirements for in-situ testing.

Over this period the R&D programmes became increasingly related to performance assessment requirements, and individual experimental proposals underwent a systematic ranking and selection procedure. Serving as an example, the key areas of interest, related questions and the resulting experiments of GTS Phase IV (1994-1996) are summarised in Table 1. An overview of the Phase IV experiments and further literature references are given in Nagra Bulletin No 27. Since its report, all these experiments have been finalised and the Phase IV Technical Reports will be published mid 1998.

In 1994, the decision was made to curtail basic research and to focus instead on key study areas identified in ongoing repository projects and their associated performance assessments. With URL programmes becoming more mature, the visible benefit of the R&D programmes is increased through i) the application of experience to integrated experiments, ii) the demonstration of the feasibility of repository siting, construction and iii) the validation of the predictions made. Increasing emphasis is also laid on the investigation of the interactions of the Engineered Barrier System (EBS), the groundwater and radioactive waste.

The specific transferability of results from the GTS- programmes to the repository projects and associated performance assessment have improved due to the more systematic planning and experiment-selection procedures applied. Methodologies and equipment developed can be transferred to other sites, e.g. to the Mont Terri Project. On the basis of existing databases and experience in design calulations, new programmes can be initiated in a cost- and time-effective way. The different approaches made in recent years to develop, test and validate numerical and conceptual models for radionuclide transport- and two-phase flow processes and the integral assessment of the EBS-system behaviour in a "realistic" environment are considered to be major outputs obtained from the GTS.

With the decision at the end of 1996 to continue operation of the GTS until the year 2002, Nagra and its partner organisations developed a GTS Phase V Programme. For Nagra's activities, the following general objectives were set:

• Performing long-term experiments to evaluate the interaction between geological and engineered barriers.
• Demonstrating both the technical feasibility and efficiency of engineered barrier systems; optimising emplacement and operating procedures under realistic conditions.
• Further studies on validating the predictions of safety-relevant models.
• Providing input to public information programmes, with a view to increasing public confidence (acceptance).
• Maintaining know-how and also integrating new scientific/technical information into existing investigation concepts.

The Phase V experiments and the participating organisations are listed in Table 2. Currently, 12 partner organisations from 9 countries are involved in GTS Phase V, with active contribution either as ''Experiment Leader'' or as ''Experiment Partner''.

Table 2. GTS Phase V 1997 - 2002 Experiments and Participating Organisations
(* Radiotracer experiments performed in the radioprotection zone of the GTS)

It should be noted here that the concept of Phase V is flexible, in that the existing infrastructure, the know-how, and databases can be provided for new proposals which need not necessarily be related to the issue of radioactive-waste disposal .

The focus of GTS Phase V is on programmes related to the demonstration of the technical feasibility and efficiency of engineered barrier systems (EBS) under realistic conditions with two large-scale experiments: The FEBEX Experiment (Huertas & Santiago, 1998) for the full-scale demonstration of the disposal concept for HLW, initiated in 1995, and the GMT Experiment, initiated in November 1997, aiming at the demonstration of the construction and emplacement of EBS for a L/ILW silo-type repository (~ 1:10 scale). The main objective of these large-scale experiments are the evaluation of the capability of current modelling codes and the testing of predictions for i) the coupled thermal, hydraulic and mechanical system behaviour and ii) the gas transport processes under two-phase flow conditions. It is planned to complete the experiments in 2002/3 and to compile results in final synthesis reports.

Thematically related to gas transport through the EBS is the GAM Experiment, concentrating on the two phase flow processes in water-conducting features. These are considered to be the main transport pathways for gas generated by metal corrosion or degradation of organic material during the post-closure phase of a repository. The experiment aims at the identification of transport processes, determination of the influence of internal fracture heterogeneity and the evaluation of the consistency between numerical simulations and field tests.

The two experiments utilising radionuclides (HPF and CRR) will provide in-situ data to minimise the uncertainties and data base gaps in performance assessment modelling and will concentrate on the validation of the model predictions. For the HPF Experiment, the effects of the hyperalkaline plume, produced by the leaching of cement-based materials, on the retardation behaviour of the (host) rock formation are studied (particularly relevant to repositories for L/ILW or TRU). The CRR Experiment should provide improved understanding of the transport of radionuclides sorbed reversibly and/or irreversibly on colloids. In addition, data to test the thermodynamically predicted speciation of a suite of performance assessment relevant radionuclides will be provided. The data will allow the quantitative assessment of the retardation of redox-sensitive radionuclides and provide a test of current near-field radionuclide release scenarios.

The other experiments mentioned in Table 2 will provide further input to optimise site-characterisation methodologies and aim at the integration of new scientific/technical information into existing investigation concepts.

Apart from these technical and scientific objectives, the importance of public relations should be emphasised. The present concept foresees the documentation of work, not only as scientific reports, but also as videos and reports directed to the general public.

The AGS Experiment, which is in an preliminary planning stage, is one example of R&D performed at the GTS that is not related to the issue of radioactive-waste disposal. An understanding of fractured media is important in the exploitation of geothermal resources and in the modelling of subsurface transport of groundwater chemical contaminants. The AGS Experiment is primarily directed towards the use of geothermal resources by providing strategies for practical applications. Provided this experiment can be implemented in the Phase V programme, it is foreseen to follow up this field of potential investigations at the GTS more actively within the next years.

The Mont Terri underground rock laboratory is located in north-western Switzerland, in the Jura mountains. In this area, several motorway tunnels are being excavated, one through Mont Terri, with a length of about 4 km. The rock laboratory is located in the reconnaissance gallery of this tunnel. Eight niches with a maximum depth of 10 meters were excavated into the wall of the gallery at the beginning of 1996 and most of the experiments are located in these niches. A new gallery, approximately 250 metres long will be excavated by summer 1998 to house further experiments.

Figure 2. Schematic layout of the Mt. Terri Rock Laboratory
(for location see Figure 1; for explanations see Table 4)

Mont Terri is a rock laboratory in a well-consolidated, fractured shale (claystone), the Opalinus Clay, which has a water content of 4 to 12 % and an extremely low hydraulic conductivity (<10^-12 m/s). During construction of the reconnaissance gallery, neither dripping water nor damp spots were observed at the tunnel wall, even in faulted sections.

Under certain conditions, when water flows into the formation, swelling clay minerals are capable of healing fault zones and the rock thus retains a very low hydraulic conductivity. The strong interaction which occurs between the Opalinus Clay and inflowing water also means that drilling and measurement techniques used in rocks such as granite are, in many cases, not the appropriate. One of the first priorities of the project is to identify and improve suitable drilling and measurement techniques.

As in the GTS-Project, international cooperation is a key feature of Mont Terri. The project is under the patronage of the Swiss National Hydrological and Geological Survey, which holds the permits of the République et Canton de Jura for the investigation programmes and currently 8 further partner organisations (ANDRA and IPSN • France, BGR • Germany, Nagra • Switzerland, Obayashi and PNC • Japan and SKN/CEN • Belgium) are involved. The programme consists of a series of experiments and is divided into project phases, each of one-year duration. Each project partner can propose experiments and selects, for each phase, the experiments in which he wants to participate and finance.

In Phases 1&2, simple experiments were carried out to test the applicability of drilling and measurement techniques and to provide a first rough geological, hydrogeological, geochemical and rock-mechanical characterisation of the Opalinus Clay. The programme for phases 3 and 4 consists of the excavation of the new gallery and the initiation of a series of more complex experiments requiring long-term monitoring phases. Table 3 shows the questions and related experiments, which are covered by the research programme. The programme and time schedule is summarised in Table 4.

Although the Grimsel Test Site and the Mont Terri Rock Laboratory are different with respect to the investigated rock, project organisation and the experimental programmes performed, they show many similarities. For example:

• Both URLs are first generation rock laboratories with experiments providing specific input to ongoing repository programmes in Switzerland and elsewhere.
• The boundary conditions set by the project organisations allow a flexible investigation programme in terms of experiment objectives, time scales and the partners involved.
• The multidisciplinary and multi-national approach is a key aspect of the programmes.
• With project teams working in both programmes, the involved partners can directly benefit from investigations both in argillaceous and crystalline rocks.

• Research programmes up to the year 2002 have either been initiated or are in the stage of detailed planning.
• The know-how gained in the URLs is also applicable in research programmes not related to the issue of radioactive-waste disposal. The potential use of the URLs as general know-how centres will be followed up more actively in the future.

There are also some differences in the focus of the R&D programme at the GTS and Mont Terri which should be pointed out, namely:

• Within the existing radioprotected zone a series of experiments using radionuclides has already been initiated at the GTS.
• The overall objectives of the individual experiments at the GTS have progressed since 1984 from generating basic information concerning the deep geological environment to model testing and verification.
• With two ongoing large/full-scale experiments, the demonstration of disposal concepts is a key aspect in the GTS-programme.
• Some experiments in argillaceous rocks are much more complex than those in crystalline rocks due to strong coupling of hydraulic, geochemical and rock-mechanical processes.
• The excavation of the new research gallery, with the related geotechnical investigation programmes, will be the first large-scale project in fractured argillaceous rocks at Mont Terri to demonstrate the feasibility to construct emplacement tunnels in rock formations, and to gain fundamental process understanding to the effects on the rock properties caused by excavation.

1. Alexander R., Ota, K., Frieg, B., McKinley, I., 1998: The assessment of radionuclide retardation in fractured crystalline rocks; 21st Int. Symposium on the Scientific Basis for Nuclear Waste Management (in press).
2. Frick, U. 1994: The Grimsel radionuclide migration experiment - A contribution to raising confidence in the validity of solute transport models used in performance assessment; Proc. of an NEA/SKI Sympos., OECD-NEA, Paris/F, pp245-272
3. Huertas, F. & Santiago, J.L., 1998:The FEBEX Project - General Overview; 21st Int. Symposium on the Scientific Basis for Nuclear Waste Management (in press).
4. Nagra 1996: Nagra Bulletin no 27 (and references therein); Nagra, Wettingen, Switzerland

The results of all experiments performed at the GTS are published in the Nagra Technical Report series (NTB), which can be ordered at Nagra. Those of the Mont Terri will be published in the series of geological reports by the Swiss National Hydrological and Geological Survey.

Please ask for a reference list of the GTS from: Nagra (National Cooperative for the Disposal of Radioactive Waste), Hardstrasse 73, CH - 5430 Wettingen.

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