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Rock laboratories4 The role of rock laboratories

10 Grimsel Test Site Phase V

24 Mont Terri Rock Laboratory

34 2002

nagra Bulletin 34

2 3

Grimsel Test Site Phase V

Wolfgang Kickmaier Nagra, Wettingen

www.grimsel.comwww.nagra.ch

Summary

Phase V of research at the Grimsel Test

Site extends over the period 1997 to 2004.

The focus is on investigating geological

barrier effectiveness and demonstration

of disposal concepts and site charac-

terisation investigations. All the projects

were also designed to contribute to the

further development and assessment of

modelling capabilities. The experiments

aimed at demonstrating disposal con-

cepts are long-term projects which will

continue for several more years. First

results from the individual experiments

are, however, already available. Phase VI

(2003 – 2013 and thereafter) has already

been approved.

Overview of the ongoing programme 1997 – 2004

Phase V projects (1997 – 2004)

CRR Colloid and Radionuclide Retardation

CTN Conclusions on the Tunnel Near-Field (desk study)

EFP Effective Parameters

FEBEX Full-scale Engineered Barrier Experiment

FOM Fibre-Optic Sensing Systems Operational Safety Monitoring

GAM Gas Migration in Shear Zones

GMT Gas Migration Test in the EBS and Geosphere

HPF Hyperalkaline Plume in Fractured Rock

Figure 1Tunnels and caverns of the Grimsel Test Site. The facility is located around 450 metres beneath the east fl ank of the Juchlistock.

IntroductionThe Grimsel Test Site (GTS) is locat ed at an altitude of 1730 metres above sea-level in the crystalline rock of the Central Aar Massif. It is used the whole year round for conducting scientifi c projects. The main tunnel system extends over more than one kilometre (Figure 1) and was con-structed in 1983/84 using a full-face tunnel boring machine (diameter 3.5 m). Additional caverns were excavated using conventional drill and blast techniques. The GTS was extended in 1996 and 1998 to ac-commodate new experiments and, in 1990, a special controlled zone (IAEA type B/C) was set up to allow in situ

use of radionuclides.

Investigations have been ongoing since 1983, with the aim of answer-ing geological, hydrogeological, geo-physical, geochemical and engineer-ing questions. The projects can be allocated to different technical areas that are important in the process of realising a deep geological repository (Table 1). Programmes at the start of operation of the Grimsel Test Site were designed to investigate the basic feasibility of a range of technologies for site characterisation. They were also in-tended to provide an understanding of processes that are important in evaluating the safety of a geological repository.

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DesAir, Wermatswil

Photographs: Comet, Zürich

nagra Bulletin 34

4 5

Today, complex projects for char-acterising the total system (waste – engineered barriers – host rock) occupy the foreground. These are long-term projects that are often conducted on a 1:1 scale. Nagra bulletin no. 27 provided an over-view of the projects that have been conducted in the past, while the present article discusses the current investigation phase using actual

examples. Further information can be found at www.grimsel.com. The results of experiments at the GTS are published openly in the Nagra Technical Report (NTB) series.The tunnel system at the GTS is located in crystalline rocks of the Central Aar Massif. The southern part of the laboratory is characterised by the occurrence of isolated shear zones running parallel to one another.

This section of the GTS is particu-larly suitable for investigating solute transport processes in the geosphere using radionuclides (to determine the barrier effect of the geosphere). In the northern part, which is marked by fracture networks, techniques for site characterisation (e.g. geophysical investigations) are tested and further developed. As the possibility exists to extend the tunnel system if required, the GTS offers excellent conditions for carrying out experiments with a wide range of objectives. A further characteristic of the work at the GTS are the long years of interna-tional collaboration. Besides Nagra, scientists from 19 partner organisa-tions from 10 countries are involved in the programmes (see Table 2); they are supported in their work by teams from universities and other research

institutes.

Table 1The objectives of the investigation

programmes at the Grimsel Test Site have

evolved with time. The emphasis today is

increasingly on demon-stration experiments.

Table 2Besides these project

partners, a large number of organisa-tions, research insti-

tutes and engineering consultants contribute

to the success of the experiments at the

GTS.

Phase V projectsBased on the experience gained in earlier phases, it is now possible to carry out complex, long-term experiments which demonstrate the performance of a deep geological disposal system. The main objec-tives and experiment partners are summarised in Table 3. Phase V at the GTS focuses on three areas:

1. Projects to determine the geologi-cal barrier function, with inves-tigation of key processes in the geosphere, for example:

• The GAM project (see Table 3 for abbreviations) on investigat-ing the transport behaviour of gas in fractured rock.

• The HPF and CRR projects aimed at determining the retardation properties of the host rock,

considering repository-induced effects (highly alkaline cement solutions, colloid formation in the transition zone between en-gineered and geological barriers). Radionuclides are used as tracers

in these experiments.2. Projects demonstrating disposal

concepts under realistic condi-

tions:• Large-scale projects such as

FEBEX and GMT allow the interactions between the radioac-tive waste, the engineered barriers and the host rock to be evaluated. Such projects also contribute to optimisation of disposal concepts (e.g. techniques for handling and emplacement of waste). A com-ponent of the work also involves testing and further developing

measurement technologies. For example, fi bre-optic sensors are being tested under realistic con-ditions in the GMT project.

3. Further work on site characterisa-tion:

• The EFP project is aimed at improving existing investigation concepts used in site characteri-sation by integration and testing of new scientifi c and technological developments.

One aspect that all the projects have in common is the further development and evaluation of the models and databases used in safety analysis. Complementary laboratory experiment programmes are also an essential aspect of the work at the GTS.

Table 3Some of the Phase V projects are already complete. The fi eld work for the FEBEX, FOM, GMT, HPF and CRR experiments is continuing.

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nagra Bulletin 34

6 7

of contaminated groundwaters have to be considered in performance assessment and repository design studies. The two-phase transport of gas and water together is diffi cult to model because heterogeneities in the engineered barriers (fl ow-paths asso-ciated with material boundaries) and in the host rock (fl ow-paths in fault zones) have to be considered at the same time. An additional element of complexity arises from the variability of fl ow-paths in the micro-scale and the structure of the bentonite or concrete used as a component of the engineered barrier system.At the GTS, the projects “Gas Migra-tion in Shear Zones” and “Gas Migra-

tion Test in the EBS and Geosphere” are aimed at identifying safety-rel-evant processes and describing them using fi rstly conceptual, and later numerical, models. Both projects extend over a period of between 4 and 7 years and comprise a large number of individual experiments, including fi eld tests, laboratory programmes[1] and mock-up experiments (labora-tory experiments on a larger scale under controlled conditions).

[1] Use of terminology in this article: laboratory programmes = investigations in conventional laboratories, fi eld investigations = investigations in a rock laboratory.

Selected Phase V projects on gas migration, radionuclide retardation (page 18) and engineered barriers (page 21) are summarised in the fol-lowing pages.

Gas migrationAfter backfi lling and sealing of the caverns or tunnels in a geological repository, gases such as hydrogen, methane and carbon dioxide can be generated due to the corrosion of metals or chemical-microbial degradation of organic substances. Depending on the gas production rate, various scenarios for pressure build-up, behaviour of the engi-neered barrier system or migration

Figure 2Schematic representation of the GAM test area. In a shear zone accessed by boreholes, various tracer tests were conducted in order to determine gas transport behaviour.

Gas Migration in Shear Zones (GAM)The aim of the GAM project was to understand and analyse the transport of water and gas in a shear zone with heterogeneous structure. Building on the experience gained in experiments conducted in Phase IV, the 3-year programme consisted of a wide range of experiments; investigations on core samples provided additional informa-tion on shear zone structure required for interpreting the fi eld experiments. The parameter values derived from the fi eld work provided the input needed for developing the transport models (conceptual/numerical) used in the safety assessment of planned repositories.The GAM experiment was per-formed in a section of a shear zone

Figure 3Structure of the GAM shear zone and migra-tion of different tracers (schematic). Note the open channels. The thin section impreg-nated with resin shows the complex structure of the shear zone.

accessed by 20 boreholes (Figure 2); the zone has an average transmissivity of 2 to 5.10-10 m2/s. Between 1998 and 2001, hydraulic single and cross-hole tests and gas threshold pressure tests with a range of tracers were car-ried out; these included non-sorbing water-soluble tracers, particle tracers (microspheres, bacteriophages, nano-spheres) and gas tracers (e. g. helium, xenon). These tracers show differing migration behaviour, with the result that different parts of the shear zone are affected (Figure 3). Non-sorbing, water-soluble tracers undergo advec-tion and dispersion and can penetrate the entire pore space. Particle tracers circulate within the main fl ow-paths of a shear zone (assumption: saturated conditions), but do not reach narrow matrix pores with stagnant water.

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Under two-phase flow conditions (unsaturated conditions), gas tracers migrate primarily along fl ow-paths with large pore radii. During the tests, radar refl ection measurements with a high frequency borehole probe were carried out in order to visualise the fl ow-paths. In addition to this, laboratory investigations were car-ried out on samples from the shear zone to analyse the structure of pore spaces and to determine rock prop-erties such as porosity and perme-ability (two-phase fl ow parameters). Methods were also developed to extrapolate the results of the labora-tory experiments (cm-scale) to fi eld conditions (metre-scale).

1 cm

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nagra Bulletin 34

8 9

Gas Migration Test in the EBS and Geosphere (GMT)The focus of the GMT project, which is led by RWMC of Japan, is on de-termining gas transport behaviour through the engineered barriers of a radioactive waste repository. The key objectives can be summa-rised as follows:

• Determining the functioning/effectiveness of a specifi c engi-neered barrier system.

• Development and application of conceptual and numerical gas transport models.

• Providing the background infor-mation necessary for improving this engineered barrier system.

• Investigating the practicability of constructing disposal silos for par-ticular low- and intermediate-level wastes under realistic conditions.

• Determining the transferability of laboratory experiments to reposi-tory-relevant conditions (upscal-

ing).The basic set-up of the GMT project is an engineered barrier system based on a Japanese silo-type repository concept. Figure 4 shows the test layout at the GTS.

Figure 6Installation of the barrier system and instrumentation for the GMT project

November 2000:Compaction of the sand-bentonite mix-ture in the lower part of the silo.

February 2001:Completion of the concrete silo with extensive instrumenta-tion for monitoring gas transport behaviour.

March 2002:View into the GMT cavern before backfi ll-ing. To prevent any damage, all sensor cables are led in through a pipe system. Steel sheets, which act as gas collectors, are installed above the silo. After backfi lling of the cavern, the access tunnel was sealed with a concrete plug.

Following initial site characterisa-tion studies, the GMT access tunnel and the silo were excavated in 1998. Characterisation of the geological environment with a comprehensive measurement programme then took around 1 year. Installation of the engineered barrier system began in late 2000. Three of the key steps of the installation process are shown in Figure 6. The backfi ll material consists of a sand/bentonite mixture (80:20). In the centre is the concrete silo, where, in a real system, waste packages would be emplaced. Following saturation of the barrier system with water, gas (nitrogen) with different trac-ers is to be injected into the silo. A total of more than 230 sensors were installed to monitor the behaviour of the engineered barrier system during the test phases. The GMT cavern was backfilled with gravel and the tunnel section sealed with a concrete plug (2.3 metres thick). The behaviour of the engineered barriers has been monitored continuously since August 2001. Hydro-tests are carried out periodically to check sys-tem behaviour. The actual gas tests are planned for 2003. The GMT fi eld project will be completed in winter 2003/2004 with excavation of the experiment site and full interpreta-tion of the data from the fi eld and laboratory experiments.Figure 5 shows an example of the data that are monitored continuously, in this case the hydraulic pressures in the sand/bentonite mixture at the beginning of March 2002. The satu-ration behaviour can be determined by comparing the results at different points in time. These data are com-pared with predictive calculations car-ried out before the actual test began.

Figure 5Example of data acquisition in the GMT experiment. The Figure shows the hydraulic pressures in the sand/bentonite backfi ll of the GMT silo at the beginning of March 2002. The area of the concrete silo is left blank.

Figure 4In the GMT project, gas migration through the engineered barrier system of a silo-type repository and the sur-rounding rock (including a shear zone) is investigated. The test confi guration corresponds to a Japanese disposal concept.

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nagra Bulletin 34

10 11

The main objectives of the HPF experiment are:

• Determining the interactions between groundwater, high-pH solutions, radionuclides and rock.

• Determining the retention capac-ity of fractured rock under altered

conditions.• Building up a consistent database,

consisting of fi eld data, laboratory analyses and natural analogue in-

formation.• Verifying the coupled (geo chem-

ical/hydraulic) transport models

used.The core of the HPF project is a series of field tests conducted in a shear zone accessed by several boreholes. The test configuration is shown in Figure 9. Simultaneous injection of water at one location and extraction at another location in the shear zone creates dipole fl ow-fi elds with differing fl ow-path lengths and fl ow rates. Following completion of the laboratory studies and detailed characterisation of the fl ow-fi elds, a highly alkaline solution is being injected into the dipole fi eld since the end of 2000. Effects on the geochemical composition of the extracted water and changes in the hydraulic properties of the shear zone are monitored continuously. A further step is planned, in which the retardation properties of the al-tered shear zone will be examined by injection of a radionuclide cocktail (Co-60, Cs-134, Eu-152, I-129 and

I-131).

Figure 7View into the control-

led zone at the Test Site (HPF project).

Figure 8In the HPF experiment, the effects of alkaline waters on rock are investigated. Studies of a natural occurrence of alkaline waters in Maqarin (Jordan) are used as an analogue to assess the effects of long timescales.

Retardation of radionuclidesThe projects “Hyperalkaline Plume in Fractured Rock” and “Colloid and Radionuclide Retardation” are based on the experience gained in the Radio-nuclide Retardation Project in Phase IV. The new projects investigate the transport behaviour of radionuclides in the geosphere (retardation proper-ties). The main objective is to develop transport models and to verify them in fi eld experiments. Both the experi-ments look at changes in retardation properties caused by the repository installations (concrete/cement or bentonite). The experiments are conducted in the controlled zone at the GTS, as they involve the use of radionuclides (Figure 7). The fi eld tests with radionuclides are planned and conducted in close cooperation

with the Swiss Federal Nuclear Safety Inspectorate (HSK).

Hyperalkaline Plume in Fractured Rock (HPF)Signifi cant volumes of cement are used in many repository designs. This means that, when a sealed re-pository resaturates, highly alkaline cement porewaters will form. These react with the host rock to form a high-pH plume which can affect the retardation properties of the rock. The formation of a high-pH plume in the vicinity of a repository is il-lustrated schematically in Figure 8. To date, model calculations of the transport of radionuclides, taking into account geochemical interac-tions between the rock and the high-pH plume, have great uncertainties and have thus provided no conclusive

answers on the mechanisms involved. They thus need to be supported by field experiments. Depending on model assumptions – for example whether thermodynamic equilibrium is reached or kinetics play a key role – the net effect of the plume could be positive (sealing the repository completely) or negative (reducing retardation properties). This type of fundamental uncertainty is diffi cult (or impossible) to resolve in normal laboratory studies.As illustrated in Figure 8, natural analogue studies will also be used to complement the fi eld experiments at the GTS. These analogues allow conclusions to be drawn regarding long-term effects on a timescale of several tens of thousands of years.

Figure 9The tracer experiments of the HPF project are carried out in a shear zone accessed by boreholes drilled from the tunnel. Large-diameter boreholes (red) are planned for later excavation of the test fi eld.

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nagra Bulletin 34

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Colloid and RadionuclideRetardation (CRR)Most of the radionuclides emplaced in the repository will decay com-pletely within the engineered barrier system. One signifi cant component of the engineered barrier system is the bentonite buffer around the waste containers. As shown sche-matically in Figure 10, there is the possibility that bentonite colloids will erode at the contact with the

Table 4Examples of radionuclide cocktails injected into the shear zone as part of the CRR experiment.

Engineered barriersTwo experiments are being carried out at the GTS with the aim of further developing and evaluat-ing the engineered barriers: these are the “Gas Migration Test in the EBS and Geosphere (GMT)” and the “Full-scale Engineered Barrier Experiment (FEBEX)“. The GMT project has already been discussed (see p. 16).

Emplacement concept for high-level waste (FEBEX)The FEBEX project, led by Enresa of Spain, is supported fi nancially by the EU (European Union) and the Swiss Federal Offi ce for Education and Science (BBW).The Spanish and Swiss concepts for disposal of spent fuel (or high-level waste) foresee horizontal emplace-ment of the waste containers in tun-nels which are then backfi lled with

Figure 11Radionuclide concentrations measured in the extraction borehole (compared to injected concentration). The nuclides were injected in two different tracer tests – with and without colloids. Also shown are the colloid concentrations measured together with the radio nuclides. The retardation properties of the shear zone and the infl uen ce of colloids on radionuclide transport can be determined from the shape of the curve.

bentonite (see box). This disposal concept and the test confi guration at the GTS are shown in Figure 12. Irrespective of the type of host rock selected, the engineered barriers play a decisive role in ensuring the long-term safety of the repository. The main objective of the FEBEX project is to investigate the engi-neered barrier system (EBS) for a HLW repository in a natural envi-ronment on a 1:1 scale. Individual components of the EBS, such as the containers and the bentonite backfi ll, have already been tested on a smaller scale. Besides demonstrating the technical feasibility of the disposal concept, the FEBEX project can be used to check the performance (predictive capability) of coupled thermo-hydro-mechanical (THM) or thermo-hydro-chemical (THC) models. The data required for this purpose are collected continuously

by more than 600 sensors installed in the engineered barriers and the surrounding rock. The project has four main compo-

nents:• Full-scale in situ experiment at the

Grimsel Test Site.

• Mock-up experiment in Madrid (scale 1:3).

• Supporting laboratory investiga-tions.

• Development and testing of THM and THC models.

Figure 12Spanish reference concept for disposal of spent fuel (above) compared with the test layout selected for the FEBEX project (below). FEBEX II shows the situ-ation after completion of the excavation phase in August 2002.

Figure 10Colloids present in groundwater can infl uence the migration of radionuclides. The Figure shows schematically the possible interactions between colloids and radio-nuclides during transport through a shear zone.

host rock and will be transported in flowing groundwater through shear zones. Colloids are fi nely dis-tributed substances ranging in size between one nanometre and one micrometre. They are a component of natural groundwaters, but can also be formed due to the presence of the repository installations. Depending on their properties (e.g. size, charge), colloids can have the effect of either accelerating or delaying the transport of radionuclides. As with the HPF experiment, the fundamental proc-esses involved in colloidal transport are poorly understood.In this case also, laboratory experi-ments conducted on a small scale provide data of only limited appli-cation to the situation in an actual

3

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2

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7

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4Radionuclides

Bentonite

Colloids

Colloid transport

1 = Formation of a bentonite colloid2 = Radionuclides dissolved in groundwater3 = Adsorption/desorption of colloids on/from the rock surface4 = Adsorption of radionuclides on colloids5 = Filtration of colloids6 = Colloid size prevents penetration into the pore space of the rock7 = Diffusion of radionuclides into the pore space8 = Adsorption/incorporation of radionuclides on/in organic colloids

(Image size ca. 10 mm)

repository. Nevertheless, it was neces-sary to conduct a 2-year laboratory programme in advance of the actual fi eld work to determine a feasible plan for the fi eld experiment and to carry out associated predictive mod-elling. The measurement technology required for continuous monitoring of the fi eld experiment also had to be further developed.In the fi eld test, various tracers, col-loids and radionuclides are being injected stepwise into the shear zone (see Table 4). The influence of the colloids on the retardation properties of the shear zone can be determined by comparing the tracer breakthrough curves. An example of different breakthrough curves is given in Figure 11.

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6.10-5

4.10-5

2.10-5

00 100 200 300 400 500

CRR – Example of tracer breakthrough curves

Con

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ratio

n C

/m0

[ml-1

]

Time [min]

Pu-242 without colloidsPu-244 with colloidsBentonite colloids

nagra Bulletin 34

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To accommodate the experiment at the GTS, a 70-metre long tunnel (di-ameter 2.28 m) was excavated by a tunnel-boring machine in 1995. Two heater elements were installed in the last 17 metres of the tunnel; these simulate the heat-producing spent fuel containers. After backfi lling with compacted bentonite (Figure 13), the tunnel section was sealed with a 2.7-metre long concrete plug. The actual heating and monitoring phase began at the end of February 1997 and ended with one heater being switched off at the end of February 2002. Predictive calcula-tions were continuously checked against registered data, making an important contribution to the im-provement of the models. The results of the fi rst phase of the project have already been summarised in a fi nal EC report. Building on the experi-ence gained through the project at the GTS, improvements to emplace-ment concepts were made and tested as part of new projects in other rock

laboratories (see page 34). In view of the excellent results ob-tained, FEBEX Phase II was initiated in summer 2000. The objectives are basically the same as those for the fi rst phase; however, scientifi c aspects have become more pronounced, with in-depth analysis of long-term processes (e.g. saturation behaviour, changes in bentonite properties) and expansion of modelling capabilities. FEBEX II also covers areas such as quality as-surance and the possible limitations of monitoring and retrievability of

the waste.Partial excavation of the engineered barrier system and the fi rst heater was successfully completed in July 2002. Analysing the numerous samples collected will allow changes in the

material properties of the bentonite due to hydrothermal and mechanical stresses to be determined directly. The excavation phase will also provide the base data for checking geochemical model calculations. Around 300 sen-sors have been removed and around 1000 material samples collected for analysis in the laboratory. Figure 13 illustrates the excavation work in 2002 (bottom half ), compared with the installation phase in 1996 (upper half ). The project is planned to con-

tinue up to the end of 2004.

Planning of Phase VI (2003–2013 and there-after)Although the Phase V investigations will continue up to the end of 2004, planning for Phase VI has already begun. In spring 2002, Nagra’s Board approved continuation of the work at the GTS for an extended period, with funding support for at least the next 10 years.Based on the requirements defi ned by the national programmes, the specifi c features of the GTS and the experience that has been built up over more than two decades, the concept for Phase VI has the following focal

points:• Large-scale, second-generation

demonstration tests. These will build on the experience gained in FEBEX and GMT. Examples would include remote handling of waste, optimisation of the engi-neered barriers, quality assurance during emplacement, long-term monitoring (sensor technology, models for data interpretation, etc.) and technologies for waste retrieval.

• Long-term in situ experiments using radionuclides, with test con-

Figure 13Work for the FEBEX

project.

August 1996:The centrally posi-

tioned electric heater is surrounded by three

rings of compacted bentonite blocks.

November 1996: Installation of the last

bentonite layer with the instrumentation

for measuring pressure (total pressure cells)

and the cable conduits for approximately

600 sensors.

June 2002:Work during the exca-

vation phase following removal of the con-

crete plug. Although the bentonite was not

completely saturated after the fi ve-year heating phase (see

Figure 14), all the gaps (see top photograph)

had already been sealed by the swelling

process.

July 2002:The excavated heater at the entrance to the

tunnel.

ditions being adapted stepwise to coincide with the conditions in a repository (PA-relevant boundary conditions). These experiments can last several decades.

International collaboration and the associated exchange of know-how will continue to play a central role in Phase VI. Finally, a recent ini-tiative to build up an associated but Independent International Training Centre (ITC) is also being actively followed n

Figure 14Temperature and water content measurements in the bentonite between 1996 and 2002. The maximum temperature of the heaters was restricted to 100oC. The water content measurements (initial value around 13 vol.-%) show a rapid rise in the outer bentonite ring; the water content in the inner ring, close to the heater, showed hardly any increase. These data were checked by direct measurements during the excavation phase and were compared with modelling results. Heater 1 was switched off on 27th February 2002 to allow excavation.

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References 1 Albert W., Bühnemann J., Holliger K., Maurer H.R., Pratt G. and Stekl I. (1999):

“Grimsel Test Site. Further development of seismic tomography“; Nagra Technical Report NTB 97-05. Nagra, Wettingen.

2 Enresa (2000): “FEBEX project – full-scale engineered barriers experiment for a deep geological repository for high level radioactive waste in crystalline host rock. Final report“; Publicaciones técnicas 1/2000. Enresa, Madrid.

3 Marschall P., Brodsky N., Mayor J.-C. and Meier P. (2001): “Solute and gas migration experiments in a heterogeneous shear zone“; Proceedings of the 8th international high-level radioactive waste management conference (April 29 - March 3, 2001), Alexis Park Resort, Las Vegas.

4 Marschall P., Fein E., Hull K., Lanyon W., Liedtke L., Müller-Lyda I. and Shao H. (1999): “Grimsel Test Site. Investigation Phase V (1997-2002). Conclusions of the tunnel near-fi eld programme (CTN)“; Nagra Technical Report NTB 99-07. Nagra, Wettingen.

5 Marschall P. et al. (in prep.): “Grimsel Test Site. Solute and gas transport experiments in a heterogeneous shear zone (GAM shear zone)“; Nagra Technical Report. Nagra, Wettingen.

6 Möri A., Frieg B., Ota K. and Alexander W.R. (in prep.): “Grimsel Test Site. The Nagra-JNC in situ study of safety relevant radionuclide retardation in fractured crystalline rock. III: The RRP project fi nal report“; Nagra Technical Report NTB 00-07. Nagra, Wettingen.

7 Nagra (1996): “Grimsel Test Site (GTS)1996“; nagra bulletin no. 27. Nagra, Wettingen.

8 Pfi ngsten W. and Soler J.M. (2002, in prep.): “Modelling of non-reactive tracer dipole tests in a shear zone at the Grimsel Test Site“; Journal of Contaminant Hydrology.

9 Smith P.A., Alexander W.R., Heer W., Fierz T., Meier P.M., Baeyens B., Bradbury M.H., Mazurek M. and McKinley I.G. (2001): “Grimsel Test Site. Investigation Phase IV (1994-1996). The Nagra-JNC in situ study of safety relevant radionuclide retardation in fractured crystalline rock. I: Radionuclide migration experiment – Overview 1990-1996“; Nagra Technical Report NTB 00-09. Nagra, Wettingen.

10 Vomvoris S., Marschall P., Kickmaier W., Ando K., Fukaya M., Fujiwara A. and Kaku K. (2001): “GMT – A large-scale in-situ test of the gas migration properties of engineered barriers“; Scientifi c Basis for Nuclear Waste Management XXIV: Symposium August 27 - 31, 2000, Sydney. MRS-Symp. Proceedings Vol. 663. Materials Research Society, Warrendale.

Complete list of Nagra Technical Reports: www.nagra.ch.

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