Friction Stir Welding (FSW) is a novel solid-state joining process where the work pieces are joined together using a rotating non-consumable tool. The process has mainly been used for joining aluminium alloys, and has not yet been used in production for any other metal. However, the results from the development program confirm that FSW can consistently seal 50mm thick copper canisters without creating defects. A new machine is now installed at SKB's Canister Laboratory to further automate the process to production level.

To ensure safe storage of nuclear fuel waste, copper canisters are proposed as corrosion barrier. One alternative for sealing the copper canisters is Friction Stir Welding (FSW). During the joining process friction heat and mechanical deformation appear between the rotating tool and the material being welded. Liquid metal will not form, since this is a solid state welding process. Three distinct microstructural zones are developed namely the nugget, the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ). The nugget is in the centre of the weld, where the pin is located and where severe plastic deformation occurs that leads to recrystallisation. Surrounding the nugget, the TMAZ is only partially recrystallised, due to lower temperature increase and deformation compared to the nugget. The third zone, HAZ, surrounds the TMAZ. The initial nugget can have a classic round aluminium nugget image, when the welding conditions are cold, but the steady state nugget, is wider near the shoulder and shorter in the weld root.

Cylindrical copper electrodes have been installed in a test parcel at the Äspö Hard Rock Laboratory and real-time corrosion monitoring was initiated in May 2001. The test parcel was emplaced on October 29, 1999, and will be retrieved in 2004. The three electrodes, each of about 100 cm2 surface area, are installed in bentonite block 36, where the temperature is about 24°C.

The corrosion monitoring is performed with linear polarization resistance (LPR), harmonic distortion analysis (HDA) and electrochemical noise techniques. A value on the Stern-Geary coefficient is required to calculate the corrosion rate from the measured LPR data. A default value of 10.3 mV has been used, but an actual value can in fact be obtained from the HDA. The corrosion rate will be overestimated if the frequency of the voltage perturbation for the LPR measurements is not low enough. Electrode impedance measurements have been performed to verify this.

Two and a half year after emplacement the recorded corrosion rate of copper in the above bentonite block amounts to about 2.2 μm per year (using a default value of 10.3 mV for the Stern-Geary coefficient and a 0.01 Hz voltage perturbation frequency). The actual corrosion rate is estimated to less than 0.7 μm per year (considering a measured Stern-Geary coefficient of 6.5 mV and the findings from the electrode impedance measurements).

Stainless steel is being envisaged as the primary candidate container material for the final disposal of vitrified HLW in deep geological argillaceous formations in Belgium. The impact of an evolving underground repository environment, i.e. a progressive change from oxic to anoxic conditions (due to the consumption of entrapped oxygen), on the pitting behaviour of austenitic stainless steels AISI 316L hMo and UHB 904L was studied. CPP-experiments were performed in synthetic solutions, which are representative for the near-field chemistry of an underground repository. The solutions contained various amounts of Cl- (100–50,000 mg/L) at near-neutral pH. Experiments were conducted at 16 and 90°C.

AISI 316L hMo and UHB 904L will not be subjected to immediate pitting problems neither under oxic, nor under anoxic conditions. However, AISI 316L hMo could present long-term pitting problems under oxic conditions. Pits are much easier initiated on AISI 316L hMo, for both oxic and anoxic conditions. The pits propagate in a rather similar manner under oxic conditions for both alloys, whereas under anoxic conditions the pits formed on AISI 316L hMo are much deeper. AISI 316L hMo is more susceptible to crevice attack.

This study [1] was performed for SKB (Swedish Nuclear Fuel and Waste Management Co) within the framework of the assessment of the long-term safety of a deep repository for spent nuclear fuel.

Subsequent to work performed by [5], SKB decided to carry out additional hydrogeological modelling studies related to glaciation effects at Äspö. In particular, subglacial groundwaterflow and the impact assessment on a repository required further studies. The presence of subglacial groundwater flow beneath ice sheets is due to basal melting occurring during glaciation periods.

As compared to the previous model [5], the domain geometry and processes involved remained identical but this time numerical calculations are performed with the NAMMU program. Modified assumptions corresponding to specific boundary conditions were implemented and additional variations of the base case were simulated.

Atomic Energy of Canada Limited (AECL) has been conducting detailed geological, geophysical and geotechnical investigations in plutonic rocks at several research areas. The main focus of the work was on developing and testing site evaluation and site characterization methods to investigate progressively smaller volumes of plutonic rocks in greater details. In this process extremely detailed airborne, surface and borehole geophysical surveys were done to identify fractures and understand groundwater flow conditions. A brief review of geophysical methods, which demonstrate the area scale, site scale and vault scale characterization techniques has been included in this paper. The boreholes in the Whiteshell Research Area (WRA) of Lac du Bonnet Batholith and at its Underground Research Laboratory (URL) excavated to 420 m depth have provided extensive opportunities to develop and test these methods. One example of geophysical surveys associated with the Moderately Fractured Rock (MFR) experiment at 240 Level is discussed in some length.

Disposal in deep, stable bedrock is currently one concept for isolating high-level wastes from the environment. Repository for high-level waste in rock excavated using different drilling techniques is surrounded by an excavation damaged zone (EDZ) which properties have been changed. The micro fracturing of samples taken from the experimental deposition holes in the underground Hard Rock Laboratory at Äspö were investigated by the 14C polymethylmetha-crylate (14C-PMMA) method and scanning electron microscopy (SEM) to evaluate the impact of EDZ on migration. The porosity of the damaged rock zone is clearly higher than the porosity of undisturbed rock. The thickness of the crushed zone with significantly higher porosity is a few millimetres and the average depth of the damaged zone (i.e. a clear increase in porosity found) is from 5 to 20 mm from the hole wall. The apertures of the inter- and intragranular fractures in the crushed zone varied from 5 to 30 μm according to SEM examination. Earlier results of porosity, diffusivity and permeability measurements in granites were compiled and the results of the porosity values of Äspö diorite were compared to the porosity values measured in other types of granites. The results were compiled in permeability-diffusivity-porosity space and were found to form a plane that could be used to estimate the range of diffusivity and permeability of the Äspö diorite.

Existing fractures crossing a deposition hole may be activated and sheared by an earthquake. The effect of such a rock shear has been investigated in a project that includes both laboratory tests and finite element calculations.

A number of laboratory tests have been performed with shearing of water-saturated bentonite samples at different densities and shear rates. From those tests a material model of the buffer that takes into account the shear rate has been formulated. Shear rates up to 6 m/s have been tested.

The rock shear has been modelled with finite element calculations with the code ABAQUS. A 3D finite element mesh of the buffer and the canister has been created and a number of calculations with simulation of a rock shear have been performed. The rock shear has been assumed to take place perpendicular to the canister axis in either the centre of the deposition hole or at the ¼ point. The shear calculations have been driven to a total shear of 20 cm. Buffer densities at water saturation between 1950 and 2100 kg/m3 and shear rates between 0.0001 and 1000 mm/s have been modelled. The influence of buffer density, shear plane location, the shear rate and the magnitude of the shear displacement are analysed and discussed.

The results show that the influence of especially the density of the buffer and the location of the shear plane are very strong but also that the shear rate and the magnitude of the shear displacement have a significant effect.

The site characterization for the construction of the repository of spent nuclear fuel is carried out at Olkiluoto in Finland. The results of geological, geophysical, and hydrogeological investigations are integrated in a bedrock model to describe rock types, fractured zones and potential hydraulic connections. In modelling it is essential to determine structures important for construction of underground facilities. This question encompasses objectives and scale of the modelling. Important parameters in structural modelling are fracture frequency and hydraulic conductivity. The definitions need to be evaluated site-specific, because the geological circumstances control the properties of structures. An important issue is the possible existence of a boundary zone close to structures.

The Japan Nuclear Cycle Development Institute (JNC) is undertaking research into the deep geological environment in Japan in the Tono area of Japan. In the Mizunami Underground Research Laboratory (MIU) Project, located in the Tono area, JNC is carrying out surface-based investigations and will excavate an Underground Research Laboratory (URL) in order to establish comprehensive techniques for investigating and characterising the geological environment. The MIU Project focuses on the investigation of the granitic rocks of the Toki Granite. The geological structure and hydrogeological properties of the Toki Granite are closely affected by the regional fracture zones and faults. The interpretation of these features is undertaken in 3D and directly linked into 3D hydrogeological models. Significant uncertainty exists in the 3D interpretation of the fracture zones, and geologists must make several assumptions regarding the 3D structure in order to develop the 3D interpretation. In order that these assumptions are communicated to the hydrogeologists, a methodology has been developed for representing uncertainty in the 3D geological models. An important part of the uncertainty representation, is the development of a fracture zone classification in which the uncertainty in both the presence and the geometry of the fracture zone is assigned. Other elements include the development of alternative models, visualisation of raw data, development of conceptual models, development of bounding models, and suitable quality assurance and archiving of modelling projects.

Redox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.

For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.

The accurate hydraulic characterization of low permeability geological materials and formations has important practical implications, such as the geological disposal of radioactive nuclear waste. In this paper, we discuss pressure pulse techniques, which are methods that are commonly adopted both in the laboratory and in situ for testing low permeability geological materials and formations. The results obtained in this study illustrate that: 1) the use of nominal values for water compressibility will lead to significant underestimation of permeability from the pressure pulse tests; 2) specific storage is also an important parameter that should be evaluated simultaneously with permeability; 3) to shorten the time required to measure low permeability in the laboratory, it is advisable to use disk-shaped specimens; 4) when a geological formation is anisotropic, the value of permeability calculated using an isotropic model is between the maximum and minimum permeabilities of the geological formation; 5) the values of permeability and specific storage derived from an in situ pressure pulse test may only reflect the hydraulic properties of the domain closely surrounding the test well. Caution should be exercised when interpreting data derived from the pressure pulse tests for the purpose of safety assessment.

In the context of geological repositories for nuclear waste disposal, the goal of site characterisation (SC) is to obtain input data that can later be used as a basis for performance assessment calculations (PA). Performance assessment is required to give an indication as to whether the repository will behave as intended over the geological timescales relevant for risk analysis.

Processes that may be important in a PA setting for constraining radionuclide transport may not necessarily be dominating, or indeed may not even be observable during SC investigations.

In this paper it is shown that the migration of sorbing tracers is governed largely by surface sorption phenomena in typical SC-type field experiments whereas in a PA scenario, matrix interaction instead can be expected to play an overwhelmingly important role. This study uses data and settings that are representative for fractured rocks in Sweden, but the method used and the conclusions may have more general applicability.

Petrographic microscopy, scanning and transmission electron microscopy, X-ray diffractometry, surface area and cation exchange analyses have been undertaken on a suite of ‘bulk’ and size separated sediment fractions from the Drigg site. The data indicate a complex phyllosilicate assemblage consisting of illitic and vermiculite material derived from the complex weathering history of the siliceous, micaceous, feldspathic and chloritic parent clasts. Coarse grains range from clean fresh looking ‘polished’ clasts to heavily coated with iron oxides and oxyhydroxides. The surfaces of most igneous clasts (granites and volcanics) are usually highly altered to micaceous (‘illitic’), chloritic and vermiculitic clays. Carbonates, such as calcite, dolomite and siderite, are present, particularly in the more shallow formations. The properties of the sediments have a clear impact on the evolution of groundwater chemistry. Redox conditions are consistent with equilibrium between iron oxyhdroxides and siderite, both present in Drigg sediments. Drigg groundwater samples are close to equilibrium with calcite, which not only controls the concentration of dissolved calcium and bicarbonate ions, but also the groundwater pH. Concentrations of potassium and magnesium are controlled by ion exchange reactions, while both mineralogical and groundwater evidence show that some weathering of aluminosilicate minerals is occurring, although equilibrium is not reached.

Uranium-series disequilibrium (USD) method is the only paleohydrogeological method that for the time scale relevant for performance assessments can detect and directly date past hydrogeochemical changes. Such changes cause U mobility which is seen as uranium-series disequilibrium. We have reviewed the method taking into account experimental and interpretation aspects and identified pros seem to outweigh identified cons. Reported USD studies in Finland and Sweden have earlier been mostly qualitative but a quantitative methodology has been developed for future studies.

Uranium is a redox-sensitive element which occurs naturally in the bedrock and groundwaters in Fennoscandia, and can be used, in conjunction with its decay series descendants, to indicate groundwater redox conditions. Not only can contemporary conditions be characterised, but evidence of past changes (e.g. during the last glaciation some 10 ka ago) can be preserved in minerals which coat the fracture walls along groundwater pathways. Uranium decay series data for groundwaters and solid fracture phases from the site of the Äspö Hard Rock Laboratory and its near vicinity are presented and discussed in the context of redox conditions.

Prior to the selection of the site for nuclear waste disposal, the performance of the repository is assessed based on general geological data of sites under investigation. Once the site has been selected, the results of the site investigations are used to establish the baseline condition to monitor and evaluate the induced processes during the construction of the repository. One of the processes considered is the change in hydraulic properties in the bedrock due to excavation of tunnels and other open spaces. Within this framework, the results of natural decay series studies in rock samples from the Pyhäsalmi mine collected in the nearby of a water-conducting fracture at the depths of 1275 and 1325 m may give insights on the influence of the excavation-induced changes, if any, in the groundwater flow. The spatial and temporal scale of these changes is also evaluated. The methodology used in this work could be applied to add confidence in the establishment of the baseline conditions to better assess the evolution of changes in groundwater flow patterns during and after construction of a repository system.

In order to investigate the dissolution of plutonium(III) under reducing condition and in a carbonate rich water solid phases of plutonium hydroxide and carbonate were made. The still wet solid phases were placed in vessels which contained 1 M NaClO4. The atmosphere in the vessels was either H2 or a mixture of H2 and 0.03% CO2.

The preliminary results shows that after some time the plutonium concentration in the solutions reached a value between 10−9 M and 10−7 M. The pH in the solutions is dependent of the atmosphere. In a pure H2 atmosphere the pH is changing over time whereas in the H2+CO2 atmosphere the pH stays between 7 and 7.5. At pH 8 the total carbonate concentration in the water was between 10−4 M and 10−3 M. This is the same order of magnitude as the ground water surrounding the proposed repository.

Carbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the presence of corrosion products of iron in buffer material is important to discuss the migration behavior of redox-sensitive radionuclides. Plutonium electromigration experiments in bentonite have been carried out with source of iron ions supplied by anode corrosion of iron coupon. Plutonium migrated from the iron anode toward cathode as deep as 1 mm of the interior of bentonite within 24 h. Thus plutonium chemical species would have positive charge and were estimated as PuOH2+ or PuCl2+ by the thermodynamic calculation.

In-diffusion experiments for Cs+ and I− in sandstone were performed as a function of ionic strength ([NaCl]=0.01, 0.51M) and tracer concentration ([CsI]=7.5E-5, 1.5E-2M) together with the measurements of the physical and chemical properties of sandstone, and apparent diffusivities (Da) for Cs+ were obtained. The obtained Da-values for Cs+ scarcely depended on [NaCl], but increased with increasing [Cs+]. This trend is consistent with that of rock capacity factors (α), indicating that distribution coefficient (Kd) onto sandstone and effective diffusivity scarcely depend on [NaCl]. The concentration profiles of I− were all in already breakthrough. Although this indicates that I− diffusion is faster than that of Cs+, the concentration profiles of I− may have been lower than those for blank samples, judging synthetically from the correlations between α-values and the concentration profiles of Cs+ and from the concentration profiles of I− in the blank samples. Finally, the effects of [Cs+] and[NaCl] on Kd/-values for Cs+ were discussed from the viewpoint of adsorption by ion exchange and electrostatic attraction. The kd-values were considered to be combined sorption by both reactions.