Aspo Hard Rock Laboratory Research Articles

Permeability Enhancement and Fracture Development of Hydraulic In Situ Experiments in the Äspö Hard Rock Laboratory, Sweden

A new advanced protocol of progressively increased cyclic injection and pulsed injection design for hydraulic fracturing experiments was implemented at 410 m depth in the Aspo Hard Rock Laboratory in Sweden. A monitoring array was installed around the tested horizontal borehole to detect the acoustic emissions and micro-seismic events during the fracturing process. The aim is to identify optimized injection schemes to reduce the seismicity related to the fracturing processes. The cyclic stimulation scheme of loading and unloading the fracturing net pressure leads to a lower accompanied seismicity if compared to the conventional hydraulic fracturing with constant flow rates. The related permeability of the tested rock interval can be increased, but this increase is less pronounced than that of the conventional treatments and, especially, if compared to the last of the re-fracturing series with high seismicity increase. Despite these limitations, in field applications with expected high risk of unwanted seismic events, this advanced protocol can be a feasible option to reduce this risk.

Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Äspö Hard Rock Laboratory site, Sweden

Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Aspo Hard Rock Laboratory site, Sweden

Characterization of Hydraulic Fractures Growth During the Äspö Hard Rock Laboratory Experiment (Sweden)

A crucial issue to characterize hydraulic fractures is the robust, accurate and automated detection and location of acoustic emissions (AE) associated with the fracture nucleation and growth process. Waveform stacking and coherence analysis techniques are here adapted using massive datasets with very high sampling (1 MHz) from a hydraulic fracturing experiment that took place 410 m below surface in the Aspo Hard Rock Laboratory (Sweden). We present the results obtained during the conventional, continuous water injection experiment Hydraulic Fracture 2. The resulting catalogue is composed of more than 4000 AEs. Frequency–magnitude distribution from AE magnitudes (MAE) reveals a high b value of 2.4. The magnitude of completeness is also estimated approximately MAE 1.1, and we observe an interval range of MAE between 0.77 and 2.79. The hydraulic fractures growth is then characterized by mapping the spatiotemporal evolution of AE hypocentres. The AE activity is spatially clustered in a prolate ellipsoid, resembling the main activated fracture volume (~105 m3), where the lengths of the principal axes (a = 10 m; b = 5 m; c = 4 m) define its size and its orientation can be estimated for a rupture plane (strike ~123°, dip ~60°). An asymmetric rupture process regarding to the fracturing borehole is clearly exhibited. AE events migrate upwards covering the depth interval between 404 and 414 m. After completing each injection and reinjection phase, the AE activity decreases and appears located in the same area of the initial fracture phase, suggesting a crack-closing effect.

Assessing the utility of trace and rare earth elements as biosignatures in microbial iron oxyhydroxides

Microbial iron oxyhydroxides are common deposits in natural waters, recent sediments and mine drainage systems and often contain significant accumulations of trace and rare earth elements (TREE). TREE patterns are widely used to characterize minerals and rocks, and to elucidate their evolution and origin. Whether and which characteristic TREE signatures distinguish between a biological and an abiological origin of iron minerals is still not well understood. Long-term flow reactor studies were performed in the Aspo Hard Rock Laboratory to investigate the development of microbial mats dominated by iron-oxidizing bacteria, namely Mariprofundus sp. and Gallionella sp. The experiments investigated the accumulation and fractionation of TREE under controlled conditions and enabled us to assess potential biosignatures evolving within the microbial iron oxyhydroxides. Concentrations of Be, Y, Zn, Zr, Hf, W, Th, Pb, and U in the microbial mats were 1e3- to 1e5-fold higher than in the feeder fluids whereas the rare earth elements and Y (REE+Y) contents were 1e4 and 1e6 fold enriched. Except for a hydrothermally induced Eu anomaly, the normalized REE+Y patterns of the microbial iron oxyhydroxides were very similar to published REE+Y distributions of Archaean Banded Iron Formations. The microbial iron oxyhydroxides from the flow reactors were compared to iron oxyhydroxides that were artificially precipitated from the same feeder fluid. These abiotic and inorganic iron oxyhydroxides show the same REE+Y distribution patterns. Our results indicate that the REE+Y mirror quite exactly the water chemistry, but they do not allow to distinguish microbially mediated from inorganic iron precipitates. All TREE studied showed an overall similar fractionation behavior in biogenic, abiotic and inorganic iron oxyhydroxides. Exceptions are Ni and Tl, which were only accumulated in the microbial iron oxyhydroxides and may point to a potential usage of these elements as microbial biosignatures.

Sampling and Characterizing Rare Earth Elements in Groundwater in Deep-Lying Fractures in Granitoids Under In Situ High-Pressure and Low-Redox Conditions

Several countries are preparing to dispose of radioactive nuclear waste deep underground in crystalline rock. This type of bedrock is commonly extensively fractured and consequently carries groundwater that serves as a medium for transporting metals and radionuclides. A group of metals of particular interest in this context is the rare earth elements (REEs), because they are analogues of actinides contained within radioactive waste and are tracers of hydrological pathways and geochemical processes. Concentrations of REEs are commonly low in these groundwaters, leading to values below detection limits of standard monitoring methods, particularly for the heavy REEs. We present a new technical set-up for monitoring REEs (and other trace metals) in groundwater in fractured crystalline rock. The technique consists of passing the fracture groundwater, commonly under high pressure and containing reduced chemical species, through a device that maintains the physicochemical character of the groundwater. Within the device, diffusive gradient in thin-film (DGT) discs are installed in triplicate. With this set-up, we studied REEs in groundwater in fractures at depths of approximately −144, −280, and −450 m in granitoids in the Aspo Hard Rock Laboratory in southern Sweden. The entire REE suite was detected (concentrations down to 0.1 ng L−1) and was differently fractionated among the groundwaters. The shallowest groundwater, composed of dilute modern Baltic Sea water, was enriched in the heavy REEs, whereas the deeper groundwaters, dominated by old saline water, were depleted in the heavy REEs. Deployment periods varying from 1 to 4 weeks delivered similar REE concentrations, indicating stability and reproducibility of the experimental set-up. The study finds that 1 week of deployment may be enough. However, if the overall setting and construction allow for longer deployment times, 2–3 weeks will be optimal in terms of reaching reliable REE concentrations well above the detection limit while maintaining the performance of the DGT samplers.

Stochastic inverse modelling of hydraulic conductivity fields taking into account independent stochastic structures: A 3D case study

Major factors affecting groundwater flow through fractured rocks include the geometry of each fracture, its properties and the fracture-network connectivity together with the porosity and conductivity of the rock matrix. When modelling fractured rocks this is translated into attaining a characterization of the hydraulic conductivity (K) as adequately as possible, despite its high heterogeneity. This links with the main goal of this paper, which is to present an improvement of a stochastic inverse model, named as Gradual Conditioning (GC) method, to better characterise K in a fractured rock medium by considering different K stochastic structures, belonging to independent K statistical populations (SP) of fracture families and the rock matrix, each one with its own statistical properties. The new methodology is carried out by applying independent deformations to each SP during the conditioning process for constraining stochastic simulations to data. This allows that the statistical properties of each SPs tend to be preserved during the iterative optimization process. It is worthwhile mentioning that so far, no other stochastic inverse modelling technique, with the whole capabilities implemented in the GC method, is able to work with a domain covered by several different stochastic structures taking into account the independence of different populations. The GC method is based on a procedure that gradually changes an initial K field, which is conditioned only to K data, to approximate the reproduction of other types of information, i.e., piezometric head and solute concentration data. The approach is applied to the Aspo Hard Rock Laboratory (HRL) in Sweden, where, since the middle nineties, many experiments have been carried out to increase confidence in alternative radionuclide transport modelling approaches. Because the description of fracture locations and the distribution of hydrodynamic parameters within them are not accurate enough, we address the domain by using a pseudo porous media approach, in which fractures are represented by high K zones. This approach has already been proven to be successful in real case studies. Results of the K conditional fields have been compared to those obtained in a scenario where the independence of the different stochastic structures was not fully considered. After performing an uncertainty assessment, we have found that when using additional conditioning data (piezometric head data) and multiple SPs the reproduction of the hydraulic head field is significantly improved and uncertainty is reduced. However, honouring the independence of different SPs does not warrant a decrease of uncertainty but in fact due to a more realistic reproduction of the statistical features uncertainty can be increased.

FRACOD Modeling of Rock Fracturing and Permeability Change in Excavation-Damaged Zones

The characterization of the excavation-damaged zone (EDZ) around an underground excavation is a major research topic for deep geological disposal of medium- to high-level radioactive waste. Rock fracturing because of excavation and thermal loading and its resultant rock mass permeability change in the EDZ are important for construction projects and long-term safety. A new function to predict rock mass permeability change in fractured rocks has been developed and added to the existing fracture mechanics code FRACOD. The new functions in FRACOD have been applied to predict the extent of EDZ and permeability change in the vicinity of the tunnel sealing experiment (TSX) tunnel of the Underground Research Laboratory (Canada), the zone of excavation disturbance experiments (ZEDEX) tunnel of the Aspo Hard Rock Laboratory (Sweden), and the deposition tunnels in crystalline and sedimentary rocks (Japan). The predicted EDZ and its permeability are consistent with the measurement data of the TSX tunnel and ZEDEX tun...

Rock Stress, Rock Stress Measurements, and the Integrated Stress Determination Method (ISDM)

The primary objectives of this work are to (1) improve the understanding of the prevailing stress distribution at the Aspo Hard Rock Laboratory (HRL) in SE Sweden by employing an integrated stress determination approach, and in order to accomplish this (2) extend the existing stress integration methodology denominated integrated stress determination method (ISDM; Cornet in Comprehensive Rock Engineering vol 3, Pergamon Press, Oxford, pp 413–432, 1993a). The new developments of the ISDM involve a 12-parameter representation of the regional stress field in the rock mass (i.e., the full stress tensor and its variation with depth) that is applicable to hydraulic stress data (sleeve fracturing, hydraulic fracturing, and hydraulic tests on pre-existing fractures), overcoring data (CSIR- and CSIRO-type of devices), and to combinations of hydraulic and overcoring stress data. For the latter case, the elastic parameters of the overcoring technique may be solved in situ by allowing the hydraulic stress data to constrain them. As a result, the problem then involves 14 model parameters. Results from the study show that the ISDM effectively improves the precision of the prevailing stress field determination and that it is especially powerful for identification of consistencies/inconsistencies in an existing data set. Indeed, this is the very basic premise and goal of stress integration; combine all available data to achieve as complete a characterization of the mechanical stress model as possible, and not to identify a solution that fits only loosely the maximum amount of stress data.

Coupled Thermohydromechanical Modeling of the Full-Scale In Situ Test “Prototype Repository”

The Prototype Repository project represents a full-scale in situ test of the Swedish concept for high level radioactive waste disposal in deep geological repositories, being conducted at the underground Aspo Hard Rock Laboratory and managed by SKB (Swedish Agency for Radioactive Waste Disposal). Instead of canisters with radioactive material, heaters installed in cylindrical containers surrounded by compacted bentonite have been used in the test. A large number of thermohydromechanical parameters for materials used in the test were carefully determined based on the latest laboratory experiments and site investigation. After comparison among six simulation models, some valuable conclusions are made about the interaction effects of six deposition holes and the effects of thermohydrogas–mechanical coupling. A three-dimensional coupled thermohydraulic model was selected for the prediction of temperature, whereas an axisymmetric two-dimensional coupled thermohydromechanical model was selected for the predictio...

Evaluation of retention properties of a semi-synthetic fractured block from modelling at performance assessment time scales (Äspö Hard Rock Laboratory, Sweden)

Modelling of radionuclide transport in fractured media is a primary task for safety evaluation of a deep nuclear waste repository. A performance assessment (PA) model has been derived from site characterization data with the aim of improving confidence for quantifying transport of sorbing radionuclides at a safety time scale of 106 y. The study was conducted on a 200 × 200 × 200 m semi-synthetic fractured block, providing a realistic system derived from the Aspo Hard Rock Laboratory (Sweden) dataset. The block includes 5,632 fractures ranging from 0.5 to 100 m in length and a heterogeneous matrix structure (fracture coating, gouge, mylonite, altered and non-altered diorite). The PA model integrates steady-state flow conditions and transport of released radionuclides during the safety time scale. An original simulation method was developed involving Eulerian flow and transport within fracture planes with a mixed hybrid finite element scheme and a semi-analytical source term to account for heterogeneous matrix diffusion. Total mass flux of radionuclides (conservative to strongly sorbing) was computed. A method to simplify the system was demonstrated, leading to a major path of 12 fractures. This is mainly due to the low connectivity of the fracture network. Matrix diffusion and sorption proved to have major impact on block retention properties for PA conditions.

Characterising and modelling the excavation damaged zone in crystalline rock in the context of radioactive waste disposal

This paper describes current knowledge about the nature of and potential for thermo–hydro–mechanical–chemical modelling of the excavation damaged zone (EDZ) around the excavations for an underground radioactive waste repository. In the first part of the paper, the disturbances associated with excavation are explained, together with reviews of Workshops that have been held on the subject. In the second part of the paper, the results of a DECOVALEX [DEmonstration of COupled models and their VALidation against EXperiment: research funded by an international consortium of radioactive waste regulators and implementers ( http://www.decovalex.com )] research programme on modelling the EDZ are presented. Four research teams used four different models to simulate the complete stress–strain curve for Avro granite from the Swedish Aspo Hard Rock Laboratory. Subsequent research extended the work to computer simulation of the evolution of the repository using a ‘wall-block model’ and a ‘near-field model’. This included assessing the evolution of stress, failure and permeability and time-dependent effects during repository evolution. As discussed, all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress–strain curve for rock and for modelling the EDZ.

Understanding groundwater chemistry using mixing models

Abstract For the last 15 a, SKB (the Swedish Nuclear Fuel and Waste Management Company) has been using the Aspo Hard Rock Laboratory (HRL) as the main test site for the development of suitable tools and methods for the final disposal of spent nuclear fuel. Major achievements have been made in the development of a new groundwater modelling technique. The technique described in this paper is used within the ongoing site investigations of Forsmark and Simpevarp in Sweden. The limitations of existing geochemical models used at many sites and the need to decode complex groundwater information in terms of origin, mixing (transport) and reactions at site scale, necessitated the development of a new modelling tool, M3, (multivariate mixing and mass-balance calculations). In M3 modelling, the assumption is made that the groundwater chemistry is a result of mixing as well as water/rock interactions. The M3 model compares groundwater compositions (measured in terms of major ionic components, stable isotopes and 3H) at a site. The model differs from many other standard geochemical models which primarily use water–rock interactions, rather than mixing, to determine groundwater chemical evolution. The tool is not dependent on thermodynamic databases, potentially uncertain redox and pH data, and can deal with the effects of biological reactions. The results of mixing calculations can be compared or integrated with hydrodynamic models. In this paper, the M3 method has been applied to two large hydrogeochemical databases, for the Aspo Hard Rock Laboratory in Sweden, the Underground Research Laboratory in Canada (URL) together with data from the ongoing site investigations of Forsmark and Simpevarp in Sweden. Decreasing amounts of precipitation and increasing proportions of saline and brine waters are seen with increasing depth in both areas. Biogenic waters, caused by uptake of CO2 from organics causing additional formation of HCO3 by water–rock interaction, occur at intermediate depths in both areas but more glacial water is detected in the URL area. The origin and evolution of the groundwater at the Aspo and URL sites have been quantified with the aid of M3. In addition, the conceptual present/post-glacial hydrogeological model has been verified.

Characterization of microbial processes in deep aquifers of the Fennoscandian Shield

Abstract Micro-organisms must be included in any hydrogeochemical modelling efforts in the ongoing Swedish programme to characterize potential sites for the geological disposal of spent nuclear fuel. This paper presents the development and testing of several methods for estimating the total numbers of micro-organism groups and amounts of their biomass in groundwater, their diversity, and the rates of microbial processes. The enumeration and cultivation methods were tested and evaluated on groundwater from boreholes at 450 m depth in the Aspo Hard Rock Laboratory (HRL), Sweden, and from two potential sites for a final repository of spent nuclear fuel, Forsmark and Laxemar. The reproducibility of the methods between parallel samples and over time was investigated and found to be excellent. Nitrate-, iron-, manganese- and sulphate-reducing bacteria and acetogens and methanogens were found in numbers up to approximately 87,000 cells L −1 groundwater from the studied sites. A methodology that analysed microbial process rates was developed and tested under open and closed controlled in situ conditions in a circulation system situated 447 m underground in the MICROBE laboratory at the Aspo HRL. The sulphide and acetate production rates were determined to be 0.08 and 0.14 mg L −1 day −1 , respectively. The numbers of sulphide- and acetate-producing micro-organisms increased concomitantly in the analysed circulating groundwater. Flushing the sampled circulation aquifer created an artefact, as it lowered the sulphide concentration. Microbial and inorganic processes involved in sulphur transformations are summarized in a conceptual model, based on the observations and results presented here. The model outlines how dissolved sulphide may react with Fe(III) and Fe(II) to form solid phases of iron sulphide and pyrite. Sulphide will, consequently, continuously be removed from the aqeous phase via these reactions, at a rate approximately equalling the rate of production by microbial sulphate reduction.

The use of the Pareto distribution for fracture transmissivity assessment

For many applications data on the transmissivity distribution of individual fractures are necessary, i.e., discrete fracture network (DFN) modelling of groundwater flow and transport of solutes in fractured rock and design and performance of rock grouting. Using borehole data from the Aspo Hard Rock Laboratory, Sweden, it is shown that evaluated fracture transmissivities from three boreholes at Aspo can be well described by a Pareto or power-law distribution. Evaluated distribution parameters for the three boreholes are similar, which indicates that the Pareto distribution is a robust tool to assess three fracture transmissivity distributions. Using the evaluated distribution parameters random simulations of the original interval test data show that the approximate lognormal distributions of these are reproduced. This strengthens the credibility of the approach. It is shown how the distribution parameters can be assessed from incomplete data using the properties of the distribution. Finally, Pareto distribution transmissivities also imply Pareto distribution apertures of the fractures.

Estimation of rock mass strength and deformability in 3-D for a 30 m cube at a depth of 485 m at Äspö Hard Rock Laboratory

The rock fracture data provided by Swedish Nuclear Fuel and Waste Management Company were used to develop a 3-D stochastic fracture network model for a 30 m cube of Aspo diorite located at a depth of 485 m at Aspo Hard Rock Laboratory, Sweden. This fracture network model was validated. A new procedure is developed to estimate rock block strength and deformability in three-dimensions allowing for the anisotropy and incorporating the inherently statistical fracture geometry for the selected cube. The mean rock mass strength was found to be 47% of the mean intact rock strength of 297 MPa at 485 m depth. The mean rock mass modulus was found to be 51% of the intact rock Young's modulus of 73 GPa. The rock mass Poisson's ratio was found to be 21% higher than the intact rock Poisson's ratio of 0.28. These percentages indicate the level of weakening of the rock mass due to the presence of fractures. The ratio of mean major principal rock mass strength/mean minor principal rock mass strength turned out to be 1.28. The ratio of mean major principal rock mass modulus/mean minor principal rock mass modulus turned out to be 1.21.

A test of different stress measurement methods in two orthogonal bore holes in Äspö Hard Rock Laboratory (HRL), Sweden

Within the scope of works to provide the necessary rock mechanics support for site investigations for a radioactive waste repository, the Swedish Nuclear Fuel and Waste Management Co (SKB) has studied some of the available equipment for in situ stress measurements in deep boreholes. A project with the objective of comparing three different types of equipment for in situ stress measurement under similar conditions has been carried out. The tests were performed in orthogonal boreholes at the Aspo Hard Rock Laboratory (HRL), Oskarshamn, Sweden. The two most common methods to measure in situ stress are the overcoring and hydraulic fracturing methods. Among the three tests, two are carried out using the overcoring method, the third uses the hydraulic fracturing method. The overcoring equipment's are the AECL's Deep Doorstopper Gauge System (DDGS) and SwedPower's Triaxial Strain Cell (Borre Probe). The measured results could be verified against known conditions at the Aspo HRL. The results from the three in situ stress measurement methods illustrate the complexity of determining the in situ stresses in a rock mass. To understand the difference in results and answer the associated questions, it was necessary to undertake deeper investigations involving laboratory tests and theoretical calculations.

The kinetics of O2(aq) reduction during oxidative weathering of naturally occurring fracture minerals in groundwater

Aqueous chemistry methods assessed the kinetic reactivity and reduction capacity of fracture-filling minerals from a granitic groundwater environment at the Aspo Hard Rock Laboratory, a field station for research and development into the geological disposal of spent nuclear fuel. Naturally occurring fracture filling reacted with oxygenated test solutions of known composition in recirculating batch reactors.The loss of O2(aq) with time was consistent with second-order reaction kinetics where O2(aq) is consumed through reduction by reaction with structural Fe(II) at the surface of the fracture minerals. Values of the second-order rate constant (k, l mole—1 h—1) varied between experiments within the range 1.7 < log k < 2.9 and values for the total concentration of reducing sites as a measure of the reduction capacity of the mineral (St, mole g—1) varied within the range 8.5 x 10—5 < St < 4.3 x 10—4. Values for the rate constant are somewhat less than those published previously for reaction between O2(aq) and Fe(II) surface complexes; i.e. structural Fe(II) appears to be less reactive than adsorbed Fe(II)(aq) but is significantly more reactive than Fe2+.Values of the rate constant did not depend on release of network ions from the reacting minerals, and did not vary significantly with pH, mineral mass, specific surface area or mineral Fe(II) content. Oxidative weathering of sulphide minerals does not occur to any measurable extent. When corrected to rock/water ratios for granite aquifers, the rate constants correspond to a half-life for O2(aq) on the order of seconds indicating an essentially instantaneous reaction on repository time scales. Comparison of reducing capacity for the fracture fillings and oxidizing capacity for groundwater saturated with O2(aq) indicates that oxidizing fronts within the geological barrier would travel ~4000 times more slowly than the velocity of groundwater flow.

In-situ Measurements of Cutter Forces on Boring Machine at Äspö Hard Rock Laboratory Part II. Characteristics of Cutter Forces and Examination of Cracks Generated

By means of spectral analysis, the measured normal forces, tangential forces, and side forces acting on two button cutters on the boring machine in Aspo Hard Rock Laboratory were analysed and the basic characteristics of the cutter forces were determined. After the measurements of the cutter forces, some rock core samples were taken from the bottom and the wall of the test borehole. These samples were cut, polished, and examined by means of a Scanning Electron Microscope (SEM). The lengths of the major cracks in the rock samples were measured, and a relation between the length of the median cracks and the relevant cutter forces was investigated.

In-situ Measurements of Cutter Forces on Boring Machine at Äspö Hard Rock Laboratory Part I. Laboratory Calibration and In-situ Measurements

This paper presents the testing methods used and the results obtained in an investigation of the cutter forces on a Boretec DS 1.6 boring machine during field boring in Aspo Hard Rock Laboratory. Two button cutters, one front cutter and one gauge cutter, were used in the field measurements. A total of 6 strain gauges were bonded on the shaft of each cutter. And each group of two gauges was used to measure a one-orthogonal cutter force component, i.e. the normal force, tangential force, and side force, respectively. In order to measure the cutter forces successfully, a telemetry system composed of a transmitter and a receiver was employed to transfer the signals from the strain gauges to a computer. A three-direction-loading system was employed in the laboratory calibration so as to solve the force-coupling problem appearing in the cutter force measurements. Correspondingly, a mathematical treatment of the force-coupling problem was performed. Then, by means of the established testing system, which was proved successful in the laboratory, the normal force, tangential force, and side force of the two button cutters on the boring machine were measured in the field. In addition, the penetration rate, thrust, and rotation speed of the boring machine were also recorded in the field. The results show the following. (1) A force-coupling phenomenon really exists and it should be considered. (2) All three directional force components always show quite a high peak value every few seconds. (3) The cutter forces of the front cutter are always much larger than the respective cutter forces of the gauge cutter. Moreover, as expected, the normal force of each cutter is much larger than the tangential force and side force of the cutter in question.

Actinide Migration Experiment in the ÄSPÖ HRL in Sweden: Results from core #5. (Part III)

Within the scope of a bilateral cooperation a series of Actinide Migration Experiment were performed by INE at the Aspo Hard Rock Laboratory in Sweden. This report covers investigations on actinide migration in a single fractured granite sample (core #5) performed in the CHEMLAB 2 probe under in situ conditions at Aspo HRL. The same experimental setup was applied as in previous experiments. Investigations of the flow path properties and the breakthrough of inert HTO tracer are reported. Experiments with the actinides Am, Np and Pu are presented. Breakthrough of actinides was not detected within the experimental time of about four months. The different analytical techniques for determination of sorbed actinides are presented. After cutting the core in slices, the abraded material is dissolved and analyzed, the slices are used to visualize the flow path. Effective volumes and inner surface areas are measured and the results compared to batch soption studies. A prediction for the breakthrough of a further in-situ experiment is given planned for uranium as tracer.