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Wyoming-type bentonite is one of the materials to be used as part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the safe disposal of spent nuclear fuel.In the KBS-3 type repository, the canisters containing the spent fuel assemblies are surrounded by bentonite buffer. Therefore, it is necessary to understand the bentonite behaviour in shearing conditions for the long-term performance assessment of the canisters. Bentonite shearing could arise, for example, due to potential post-glacial earthquakes.The deviatoric stress at failure and the shear modulus of a compacted Wyoming-type bentonite were measured using different shearing tests. Tests were carried out on unsaturated samples at three laboratories. The shearing tests on unsaturated samples were unconfined and triaxial compression tests, hollow cylinder tests and simple shear tests. Unconfined and triaxial compression tests were also carried out on saturated samples. The failure was quite ductile when tests were carried out with confining pressure.The samples were compacted at different dry densities and degrees of saturation and tested at different confining pressures and strain levels to study their influence on the shear properties. Shear strength and shear modulus were studied based on models that consider the double porosity structure of the bentonites. Previously published triaxial tests and resonant column test results were also included in this study.In combination with these models, several alternatives for the definition of the constitutive stress were checked for the case of bentonite. A novel, approach, involving the results of mercury intrusion porosimetry in estimating the constitutive stress, was introduced.The shear strength calculated by the models showed a good agreement with the measured values. In some cases, unrealistic large tensile stresses were predicted. Furthermore, the models can assess the tendency of the shear modulus as a function of the shear strain, degree of saturation and dry density.& COPY; 2023 Elsevier Ltd. All rights reserved.

The shear modulus (G) of two different bentonites was measured by means of a resonant column apparatus. The samples were compacted at different dry densities and degrees of saturation and tested with different confinement pressures and strains levels for studying the influence of these parameters on the shear modulus. The results show similar tendencies in both bentonites: the shear modulus increases as the dry density increases and exhibits maximum shear modulus when degree of saturation is around 80%. An empirical equation, taking into account the microstructure of the clays, is used to evaluate the shear modulus at small strains as a function of dry density and degree of saturation. Although the values of the shear modulus measured are similar in both bentonites for a given stress and degree of saturation, there is difference in the elastic strain limit of the soil. Bentonite clay is going to be part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the long-term confinement of spent nuclear fuel. In order to fully understand their long-term performance, their behaviour in shearing conditions should be assessed.

This paper describes the implementation of the Bodner–Partom model for the analysis of copper corrosion barrier in canisters containing spent nuclear fuel. The Bonder–Partom constitutive model implemented in CODE_BRIGHT finite element code is compared with experimental results for validation and with the Stealth finite difference code for verification. Deep geological disposal is the most reliable alternative for the spent nuclear fuel storage. This disposal is based on the multiple barriers principle. Different barriers will prevent the release of the radionuclides and one of the barriers is the canister that will contain the spent fuel. The canister will be constructed mainly in cast iron for giving mechanical protection to the spent fuel with a copper shell for protecting the cast iron against corrosion. Due to the high strength of metals, the canister components will keep it inside the elastic region during the hydration of the buffer, so it has not been necessary to implement more accurate constitutive models for the simulation. The canister is considered more as a boundary condition rather than a component to be analysed when the hydration and swelling processes are assessed but in case of relative displacements between the lips of joints intersecting a deposition hole because of an earthquake induced by the increase of vertical load due to the accumulation of ice during a glaciation or any other tectonic effect, not likely in Baltic shield, the stresses in canister could be high enough for reaching plastic conditions and in this case, it is considered necessary to use more accurate constitutive models for the simulation of the canister–buffer system. This work has been supported by a Consortium composed by SKB (Sweden), Posiva (Finland), GRS (Germany) and ANDRA (France). The members of the steering committee of this consortium are Anders Sjöland (Chairman, SKB), Mika Niskanen (Posiva), Oliver Czaikowski (GRS) and Antoine Pasteau (ANDRA).

The KBS-3H disposal alternative is composed by horizontally placed supercontainers comprising the canisters with the spent nuclear fuel surrounded in both drift axis and radial directions by compacted bentonite blocks (buffer) enclosed in a perforated shell. The different internal gaps between the supercontainer components and the one between the buffer blocks and the host rock have direct effects on the buffer behaviour. This paper presents a Thermo-Hydraulic (TH) Three-Dimensional (3D) numerical model developed to analyse a particular geometry assuming three different gap state conditions and providing results of the temperature, liquid pressure, and evolution of the degree of saturation. The material parameters, constitutive models, and assumptions made were carefully selected with regards to laboratory measurements reported in directly-related bibliography. The modelling settles the importance of understanding the groundwater flow through the rock mass and from fractures in the rock in order to achieve reliable predictions regarding buffer saturation, since it is known that the saturation times could range from few years to one thousand years depending on the hydrogeological conditions in the rock. The obtained results lead to full saturation times of 50 to 100 years. In addition to the rock hydraulic conductivity and fracture transmissivity, the saturation process was directly affected by the material properties of the buffer and gap presence between the buffer blocks and the host rock. Finally, in connection with thermal evolution, the thermal conductivity of repository components and the behaviour of air gaps in the buffer were key variables.