Waste In Switzerland Research Articles

Facies variability and depositional cyclicity in central Northern Switzerland: insights from new Opalinus Clay drill cores

The Opalinus Clay, a silty to sandy claystone formation, Early to Middle Jurassic (Toarcian and Aalenian) in age, has been selected as the host rock for deep subsurface disposal of radioactive waste in Switzerland. Over the past thirty years, numerous geotechnical, mineralogical, and sedimentological studies have been conducted on the Opalinus Clay within the framework of the Nagra (National Cooperative for the Disposal of Radioactive Waste) deep drilling campaigns and the Mont Terri Project, an international research program dedicated to the study of claystone. The present study aims to unravel the variability of the lateral and vertical facies of the Opalinus Clay in central Northern Switzerland and to place this variability in a regional and basinal context. Analyses of new cores drilled in central Northern Switzerland, including petrographic, mineralogical (X-ray diffraction, multi-mineral interpretation), geochemical (X-ray fluorescence), statistical (non-metric multidimensional scaling analysis), and bedding dip and azimuth data, shed new light on the depositional facies and the spatial and temporal variability of the Opalinus Clay. Petrographic descriptions encompass nine new drill cores using a revised subfacies/facies classification scheme based on texture (colour, grain size, bedding) and composition (mineralogy). Particularly, one new subfacies (SF6) is described and interpreted as mass-wasting deposits. The drill cores are correlated laterally using specific marker horizons. This correlation is achieved by combining thorough facies investigations with lithostratigraphy, biostratigraphy, and chemostratigraphy. Six to seven small coarsening-upward cycles and two long-term coarsening-upward sequences can be interpreted as regressive trends. The observed trends are influenced by the interplay between sediment supply, eustatic sea level change, synsedimentary subsidence, but also the palaeogeographic configuration in an epicontinental sea, provenance and delivery of sediments, current dynamics and climate change. Finally, combined results show that the current dynamics in the Opalinus Clay has been underestimated until now and new depositional models, including the occurrence of drift deposits, are discussed.

Citizen Science-Based Waste Diaries: An Exploratory Case Study of Household Waste in Switzerland

Sustainable Development Goal 12 (SDG 12) and national waste reduction goals require frequent waste analyses for monitoring and governance decisions. We developed and tested a citizen science (CS)-based household waste diary for ten consecutive days with 89 volunteer households in Switzerland as a complementary monitoring option to official composition analyses. Discrepancies between the CS-based household diary data and the official composition analyses ranged between 55–65% less reported waste quantities for minerals, compound products, and plastics and 80–90% less for paper, avoidable food waste, and glass. Household waste diaries should be digitalized and prolonged to 21–28 days, and volunteers from different demographic groups are needed to produce stratified, representative results. We conclude that a hybrid CS study design involving waste composition analyses and waste diaries could reduce self-reporting biases while increasing the monitoring frequencies of household waste compositions. CS-based hybrid household waste projects can be a powerful means to complement the measures identified in the 2022 Swiss action plan against food waste and for data reporting for the SDG 12.3 Food Waste Index.

Constitutive modeling of clay shales in undrained conditions and its experimental verification for Opalinus Clay

Clay shales are low-permeable sedimentary rocks that exhibit inherent cross-anisotropic stiffness, strength, and permeability. Accurate design of tunnels excavated in clay shales requires appropriate constitutive models that account for the anisotropic properties of the host rock, especially under undrained conditions. This paper presents a transversely isotropic elastoplastic-damage model for fully-saturated clay shales in undrained conditions. The model describes four deformation regimes observed during consolidated undrained experiments, i.e. (1) transversely isotropic elastic deformation, (2) anisotropic plastic deformation with cross-anisotropic peak strength, (3) semi-brittle post-peak softening due to both strength and stiffness degradation, and (4) residual strength state. The performance of the model was evaluated using available laboratory tests for Opalinus Clay, the selected host rock for underground disposal of radioactive waste in Switzerland. A large experimental data set, consisting of 18 undrained triaxial compression tests, was used to back-calculate the required model parameters. The adopted experimental data include the effective stress path and the stress–strain curves of specimens with bedding orientations between 0° and 90° with respect to the loading and effective consolidation stresses between 0.76 and 16 MPa. It is shown that the proposed model adequately captures the key material features of Opalinus Clay observed in the undrained experiments.

Stress state estimation – new data and variability assessment of model results

Abstract. The upper crust of the Earth is used more and more to transport and extract raw materials and energy. It is also used for the final disposal of radioactive waste in deep geological repositories with a particularly crucial requirement for long-term safety over 1×106 years. An accurate knowledge of the hosting rock and surrounding formation coupled with comprehensive modelling is fundamental to demonstrate the geological site has the required properties for safe and long-term underground storage. Besides other criteria, geomechanics play an important role. Even if the determination of rock properties is already a challenge, the estimation of the contemporary stress state in the upper crust is even more challenging. To predict the stress state 3-D geomechanical–numerical models are used, but high-quality underground structure, rock properties and in situ stress data for model calibration are needed. In particular, data of maximum and minimum horizontal stress magnitudes (SHmax and Shmin) are required to find suitable lateral displacement boundary conditions to produce a best-fit model. During the recent exploration phase for a deep geological repository for radioactive waste in Switzerland, a unique dataset of stress magnitude data has been acquired from eight cored boreholes. Rock mechanical properties were constrained from geophysical logging and laboratory testing. The empirically correlated rock properties were not simply averaged, but a probability distribution was provided. The stress field was explored by conducting more than 120 micro-hydraulic fracturing (MHF) and dry sleeve re-opening (SR) tests in different stratigraphic units, to estimate the magnitudes of Shmin and SHmax. We present the results of a 3-D geomechanical–numerical model that shows the best fit with respect to the measured stress magnitudes. Considering the uncertainties of the MHF/SR tests and the ones resulting from rock property variability, the model can reproduce most of the measurements. However, we do show not only the best-fit result but also a bandwidth of individual stress components within a P05–P95 probability range. We also show that there are still outliers for this bandwidth, but we will show that these can be explained by scaling effects.

Potentials and limits of mechanical plastic recycling

AbstractPlastics consumption continues to steeply increase worldwide, while resultant waste is currently mostly landfilled, discarded to the environment, or incinerated. This significantly contributes to global warming and causes negative health and ecosystem effects. Increasing the circularity of plastics can reduce these impacts. This study investigated to which extent plastics' circularity can be increased by mechanical recycling. For this purpose, future scenarios involving increased waste collection, improved product design, and improved waste sorting were assessed. The system studied consists of 11 plastic types in 69 product groups consumed and arising as waste in Switzerland. By means of a material flow analysis, the amounts of consumption, waste, and secondary material utilizable in product manufacturing were quantified for the year 2040. For the waste not mechanically recycled, treatment situations mainly involving energy recovery in waste‐to‐energy plants and cement kilns were modeled. A life cycle assessment of the complete plastic material flow system was conducted. We found that the mechanical recycling rate calculated based on the utilizable secondary material can be increased to up to 31%. This can lower the plastic carbon footprint by one quarter (1.3% of today's total Swiss carbon footprint) compared to no recycling. Important barriers to a further increase of the recycling rate were inaccessibility, the large diversity of plastic grades, and contamination. The remaining impact at maximum recycling is mainly caused by polyurethanes, polypropylene, and polystyrene production. In conclusion, the potential of mechanical plastic recycling is limited, but it can, as one of several measures, contribute to combating climate change.

Structural integrity investigations of spent nuclear fuel with finite element modeling

Abstract. Radioactive waste in Switzerland will be disposed of in a deep geological repository (DGR). Responsible for the planning and preparation of realization of this task is National Cooperative for the Disposal of Radioactive Waste (Nagra). Spent fuel assemblies (SFA) constitute the main high-level waste (HLW) stream that will be disposed in the DGR. Prior to final disposal they will be transferred or transported to an encapsulation plant, where they will be loaded into final disposal canisters. To ensure that the structural integrity of SFAs is not compromised during handling and transportation, it is desirable to characterize the expected mechanical parameters of SFAs after long-term interim storage. Experimental research activities performed at the JRC Karlsruhe include safety aspects of radioactive waste management, encompassing also spent fuel storage and spent fuel/HLW disposal activities. Nagra and JRC have established a collaboration to jointly study relevant properties and behaviours of spent fuel rods, with the support of the Gösgen nuclear power plant and of Framatome, and in collaboration with other partners in Europe and internationally. As part of this collaboration, 3-point bending and impact tests were performed at the hot-cell facilities of JRC Karlsruhe, to determine the mechanical response of spent fuel rodlets under quasi-static and dynamic loads. The structural integrity of fuel rods was also evaluated under different handling scenarios using finite element (FE) analysis. Starting with the construction of a static 3D FE model of a Pressurized Water Reactor (PWR) nuclear fuel rodlet in ANSYS Mechanical, Nagra has developed a series of FE models over the years. Mechanical properties of the original rodlet model were derived through an extensive validation process, using experimental data from the 3-point bending tests. To evaluate the mechanical response of an SFA in different loading scenarios, this model was expanded using 1D beam modeling approach. The development of the simplified 1D models is shown in this presentation. In particular, the effect of the contact formulation between the spacer grid and the rods is discussed. Finally, preliminary results of the bending response of a 15×15 PWR SFA sub-model are presented.

Material flow analysis of plastic in organic waste in Switzerland

AbstractSoils have been shown to be a major sink for plastic that is released to the environment. Several agricultural practices have been identified that can result in large plastic flows onto soils, among them the use of plastic‐polluted compost and digestate. However, the magnitude of this flow is currently still unclear. The aim of this work was to quantify the flows of plastic with compost and digestate onto soils based on data from Switzerland using material flow analysis (MFA). Input data to the model were based on published data on organic waste management and plastic content in compost. In order to quantify the plastic in the biomass input, measurements were made at an anaerobic digestion plant. Together with published data on the plastic content in compost, the full fate of plastic in organic waste in Switzerland could be obtained from 1985 to 2017. 6,300 t year−1 of plastic enter the system together with organic waste, and 6,200 t year−1 are removed and are incinerated. 34.5 ± 7.1 t year−1 are contained in the solid digestate, 50 ± 11 t year−1 in compost, 12.4 ± 3 t year−1 in windrow compost and 2.0 ± 0.4 t year−1 in solid digestate from codigestion. Overall, 71 ± 11 t year−1 of plastic are transferred to agricultural soil, 22.4 ± 3.3 t year−1 to horticulture and 3.6 ± 0.7 t year−1 to private consumers. Using dynamic MFA, we predict that 1,390 ± 390 tonnes of plastic have accumulated in Swiss soils through compost addition since 1985. These values can serve as basis for evaluating the contribution of composting to the plastic pollution in soils.

Transport behaviour of low molecular weight organic compounds in multi-mineral clay systems. A comparison between measured and predicted values

Abstract Determining the retardation properties of argillaceous media for dissolved low molecular weight organic compounds (LMW—OC's) is still an open issue in the assessment of the migration behaviour of 14C in the near and far field of a deep geological repository of radioactive wastes. Here we report retardation factors of potential carriers of organic 14C (carboxylates and alcohols) in binary clay mixtures (kaolinite and illite) as well as in Opalinus Clay (OPA), the favoured host rock for the deep geological disposal of radioactive waste in Switzerland. The percolation technique with a pulse injection of the LMW-OC's was used for all measurements. The transferability of sorption values of the LMW-OC's gained on the single-mineral systems (kaolinite and illite, respectively) to the binary clay mixtures and to clay rock (OPA) was tested. For binary clay mixtures, percolation experiments were carried out using tritiated water and 36Cl− as the reference tracers. The retardation factors predicted by the component additivity approach (CA) were consistent with the measured ones. Deuterated water and bromide were used as reference tracers in experiments with OPA. Complex breakthrough curves of bromide and the test compounds were observed here. Heterogeneities of the pore space are proposed as the main reason to explain the complex structure of breakthrough curve. Additionally, (a)biotic degradation or transformation of the organic compounds over the long experimental duration possibly further added to the complexity of the results in some cases. The derivation of sorption distribution ratios (Rd), determined from the breakthrough curves was therefore inherently associated with large uncertainties. The transferability of retardation data gained on less complex systems to the conditions of OPA was tested using the CA and the global composite (GC) approach. Significant discrepancies were found between the measured values and those predicted by the CA approach. The discrepancies were found to be smaller using the GC approach. In that case, the results obtained for single- and binary clay systems were also used for calibration purposes. Retardation factors of the LMW-OC's in OPA were then predicted based on two empiric relationships. The observed discrepancies are most probably related to the different chemical composition of the aqueous solution (e.g. ionic strength, pH), the various mineralogical features (e.g. compaction), and the different hydraulic conditions within the clay systems (e.g. Darcy flux). The absence of anion-sorption in OPA may be particularly explained by differences in the pH of the OPA pore water and the pore water in compacted kaolinite samples.

Experimental study of the hydro-mechanical response of Opalinus Clay – Part 2: Influence of the stress path on the pore pressure response

Triaxial tests on back-saturated specimens using different controlled stress paths were conducted to study the influence of the stress path on the hydro-mechanical behavior of a clay shale. Opalinus Clay, a clay shale chosen for the disposal of high-level nuclear waste in Switzerland, was utilized. Three different stress paths approximating a tunnel excavation were applied: a two-dimensional stress path with isotropic initial stress conditions (i.e. pure shear compression), a two-dimensional stress path with anisotropic initial stress conditions, and a three-dimensional stress path. The influence of the stress path was investigated with respect to the specimens' geometry. Two end members were tested: specimens where the axial load was applied parallel to bedding (P-specimens) and specimens where the load was applied normal to bedding (S-specimens).Differences in the hydro-mechanical response were identified with respect to the specimens' geometry but also to the stress paths. When subjected to the two-dimensional stress paths, positive excess pore pressure was measured for S-specimens at low differential stresses whereas P-specimens showed negative excess pore pressure. The magnitudes of excess pore pressure were higher for the anisotropic two-dimensional stress path. Dilation associated with yielding was observed for all specimens. The application of the three-dimensional stress path revealed pore pressure responses that were conceptually comparable to the pore pressure response observed in situ. Pore pressure increase in front of the tunnel face can be related to poroelastic response of the rock mass to a change in differential and mean stress. Again, differences between P- and S-specimens were identified. Decrease in pore pressure before the tunnel face can be related to the dilation associated with yielding.No difference in peak strength between P- and S-specimens and the different stress paths was found. Nevertheless, it was shown that the state of failure is affected by the transversal isotropy as S-specimens fail at lower effective stresses compared to P-specimens.

Experimental study of the hydro-mechanical response of Opalinus Clay – Part 1: Pore pressure response and effective geomechanical properties under consideration of confinement and anisotropy

Consolidated drained and undrained tests with pore pressure measurements were conducted on back-saturated specimens of a clay shale to characterize the influence of confinement and anisotropy on the pore pressure response and effective geomechanical properties (i.e. first-loading E-modulus, stress at onset of dilation and peak strength). Opalinus Clay, a clay shale chosen as host rock for high level nuclear waste in Switzerland was utilized. The result showed that there is a dependency on the confinement of Skempton's pore pressure parameter A and B, the stress at the onset of dilation, and the first-loading E-modulus. Additionally, a change in behavior of the material was observed at effective consolidation stresses between 5 and 8 MPa. The specimens at lower effective consolidation stresses (i.e. heavily overconsolidated specimens) showed a dilatant behavior in the pre-peak region and a significant post-failure stress drop. Specimens consolidated at higher effective consolidation stresses (i.e. slightly overconsolidated to normally consolidated specimens) showed compaction from initial loading until post-peak and a brittle-ductile post-failure behavior. These observations were manifested in pore pressure response curves, effective stress paths and stress-strain curves. Furthermore, they could be correlated to a non-linear appearance of the peak strength failure envelope. An explanation for the non-linear failure envelope related to the dilatant structure of the material is suggested.

Discrete geometry model of heat in granular bentonite barriers

The mineral-engineered barrier in the planned repository for radioactive waste in Switzerland is being designed as a granular bentonite mixture. The infiltrating pore water from the (clayey) host rock will start to resaturate the granular barrier after its emplacement. The discrete structure of the mineral barrier requires a more detailed analysis, because the porosity alone applied in the continuum approach cannot adequately describe the heat transfer. Towards this analysis, three granular size fractions have been arranged into square or hexagonal packings and considered in the heat transfer model presented in this paper. The six different granular arrangements are set either in a planar or in a cylindrical spatial system. A major feature of the approach is providing the modelled systems with an interstitial fluid of smoothly adjustable thermophysical parameters, approximating variable water contents. The effective thermal conductivity of various systems is an important output of the model. The calculation of the temperature equilibrium period directly depends on this parameter and represents a step towards a solution for the reliable determination of the resaturation timescale. The validity of the modelled effective thermal conductivities was confirmed by laboratory experiments on real granular bentonite.

Corrosion of Copper as a Nuclear Waste Container Material in Simulated Anoxic Granitic Groundwater

Copper (Cu) is a candidate material for waste packages in geological disposal systems for high-level radioactive waste in Switzerland, Sweden, Finland, Japan, and Canada. This paper reports experimental tests of Cu in the context of radioactive waste disposal applications. Experimental tests of Cu general corrosion and hydrogen evolution were conducted under anoxic conditions (less than 10 ppb of O2) using synthetic saline groundwater based on reference compositions of deep groundwaters in crystalline rock of the Canadian Shield. The results indicate that the Cu open-circuit potential and corrosion rates in anoxic waters were very sensitive to the residual O2 concentration in solution. The corrosion rates ranged from submicrometer to micrometer per year, depending on the residual O2 concentration level. The corrosion products were predominantly cuprous oxide (Cu2O). Chlorine was present in corrosion products for tests exposed to synthetic saline groundwater, but more work is needed to assess its role in the corrosion process. Minute amounts of hydrogen were detected from the autoclave as test cell, however, they cannot be simply correlated to Cu corrosion because of complication of the autoclave material corrosion.

Anisotropic volumetric behaviour of Opalinus clay shale upon suction variation

Opalinus clay shale is under consideration to serve as the host geomaterial for the underground storage of nuclear waste in Switzerland. Water retention behaviour and anisotropic behaviour represent two main features of this geomaterial; however, a comprehensive understanding of the interaction between these two features is still lacking. This paper aims to provide a detailed experimental analysis of the coupling between the water retention capacity and the anisotropic behaviour of two facies (shaly and sandy) of the Opalinus clay shale. The response of the tested geomaterials is characterised by an unequal swelling and shrinkage response in directions parallel and perpendicular to the bedding during wetting and drying episodes. Although the shaly facies showed a higher volumetric response to suction variations, the anisotropic behaviour is more pronounced for the sandy facies.

Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland

One sector where the use of engineered nanomaterials (ENMs) is supposed to offer novel or improved functionalities is the construction industry. During the renovation or demolition of buildings, ENMs contained in former construction materials will enter recycling systems or become construction waste. Currently, information about ENM flows in these processes is insufficient. The potential for the release of ENMs from this waste into the environment is unknown, as are the environmental impacts. To evaluate whether there is currently any nano-relevant construction and demolition waste (C&DW) originating from buildings, we evaluated the sources and flows of ENMs in C&DW and identified their potential exposure pathways. A survey of business representatives of Swiss companies in this sector found that ENMs are mainly used in paints and cement. The most frequently used ENMs in the Swiss housing construction industry are nano-TiO2, nano-SiO2, nano-ZnO, and nano-Ag. Using a bottom-up, semi-quantitative approach, we estimated the flows of ENMs contained in paints along the product’s life cycle from buildings to recycling and landfill. The flows of ENMs are determined by their associated flows of building materials. We estimated an annual amount of ENMs used in paints of 14t of TiO2, 12t of SiO2, 5t of ZnO, and 0.2t of Ag. The majority of ENMs contained in paints in Switzerland enter recycling systems (23t/y), a smaller amount is disposed directly in landfills (7t/y), and a tiny fraction of ENM waste is incinerated (0.01t/y). Our results allow a qualitative determination of the potential release of ENMs into technical or environmental compartments, with the highest potential release expected during recycling.

Time-dependent fracture formation around a borehole in a clay shale

Opalinus Clay, a Mesozoic clay shale, has been chosen as host rock formation for the disposal of radioactive waste in Switzerland. For this study, borehole damage zones were utilized as a proxy for an excavation damage zone that forms around a circular, mechanically excavated tunnel in intact Opalinus Clay. Pilot boreholes were resin-impregnated and over-cored at different times after drilling, to provide insight into the time-dependent formation of fractures on both the micro- and the macro-scale. Observed fractures were characterized in terms of failure mode, their relation to the rock anisotropy, and the in-situ stress tensor.The analyses show that fractures that form in the short term initiate as shear fractures at the pilot-borehole wall and propagate parallel to bedding. Typically, a dominant shear fracture tangential to the pilot borehole wall was observed. Upon propagation of these shear fractures, wing cracks, horsetail splays and second-order shears form sub-parallel and sub-perpendicular to bedding planes, forming a complex fracture network, which extends a quarter pilot-borehole diameter into the rock mass. In the longer term, tangential shear fractures tend to propagate in a direction opposite to the initial propagation direction. In addition, new bedding-parallel fractures deeper in the rock develop, leading to the formation of thin slabs, buckling of the slabs when unsupported and eventually progression of the buckling zone deeper into the rock mass. Buckling is associated with the formation of extensional fractures normal to bedding in the center and lateral to the buckling zone. The zone of buckled rock slabs was found to have an extension of more than one borehole diameter at the time of preservation with resin.In the short term, the axis connecting the maximum failure depth on opposing sides of the borehole is parallel to the minimum stress direction in a plane normal to the borehole axis. In the long term, this axis rotates significantly towards the maximum stress direction, primarily as a consequence of tangential shear fracture propagation, slab formation and buckling. Dissipation of excess pore pressures may be the key process underpinning longer-term fracture propagation and formation.

The excavation of a circular tunnel in a bedded argillaceous rock (Opalinus Clay): Short-term rock mass response and FDEM numerical analysis

The Opalinus Clay formation is currently being investigated as a potential host rock for the deep geological disposal of radioactive waste in Switzerland. Recently, a test tunnel was excavated at the Mont Terri underground rock laboratory (URL) as part of a long-term research project (“Full-scale Emplacement (FE) experiment”) aimed at studying the thermo-hydro-mechanical (THM) effects induced by the presence of an underground repository. The objective of this paper is twofold. Firstly, the results of the rock mass monitoring programme carried out during the construction of the 3m diameter, 50m long FE tunnel are presented, with particular focus on the short-term deformation response. The deformation measurements, including geodetic monitoring of tunnel wall displacements, radial extensometers and longitudinal inclinometers, indicate a strong directionality in the excavation response. Secondly, the deformational behaviour observed in the field is analyzed using a hybrid finite-discrete element (FDEM) analysis to obtain further insights into the formation of the excavation damaged zone (EDZ). The FDEM simulation using the Y-Geo code is calibrated based on the average short-term response observed in the field. Deformation and strength anisotropy are captured using a transversely isotropic, linear elastic constitutive law and cohesive elements with orientation-dependent strength parameters. Overall, a good agreement is obtained between convergences measured in the field and numerical results. The simulated EDZ formation process highlights the importance of bedding planes in controlling the failure mechanisms around the underground opening. Specifically, failure initiates due to shearing of bedding planes critically oriented with respect to the compressive circumferential stress induced around the tunnel. Slippage-induced rock mass deconfinement then promotes extensional fracturing in the direction perpendicular to the bedding orientation. The simulated fracture pattern is consistent with previous experimental evidence from the Mont Terri URL.

Influence of superplasticizers on the long-term properties of cement pastes and possible impact on radionuclide uptake in a cement-based repository for radioactive waste

Cementitious materials will be used for the construction of the engineered barrier of the planned repositories for radioactive waste in Switzerland. Superplasticizers (SPs) are commonly used to improve the workability of concretes and, along with a set accelerator (Acc), to produce shotcrete. In this study the influence of a polycarboxylate- (PCE) and a polynaphthalene-sulphonate-based (PNS) SP on the hydration process, mineral composition and the sorption behaviour of metal cations has been investigated using an ordinary Portland cement (OPC), a low-alkali cement mix (LAC) consisting of CEM III-type cement and nanosilica, and a shotcrete-type cement mix (ESDRED) consisting of a CEM I-type cement and silica fume prepared in the presence of an alkali-free set accelerator.Both the PCE and PNS SP do not significantly influence the amount and quantity of hydrates formed during hydration. The concentration of both SPs decreased rapidly in the early stage of the hydration process for all cements due to sorption onto cement phases. After 28days of hydration and longer, the concentration of the PNS SP in the pore fluids of all cements was generally lower than that of the PCE SP, indicating stronger uptake of the PNS SP. The formate present in the Acc sorbs only weakly onto the cement phases, which led to higher aqueous concentration of organics in the ESDRED cement than in OPC and LAC.Sorption experiments with 63Ni, 152Eu and 228Th on a cation exchange resin indicate that, at concentrations above 0.1gL−1, the two SPs could reduce sorption of metal cations. Thermodynamic modelling further indicates that radionuclide complexation by formate at the concentration level in Acc can be excluded, suggesting that the apparent effect of Acc in the sorption measurements on the resin can be attributed to colloids formed owing to the high concentrations of Al and S in Acc. Sorption studies with the same radionuclides on hardened cement paste (HCP) in the presence of concrete admixture solutions and pore fluids squeezed from cement pastes further revealed no significant effect on sorption by either the concrete admixtures or their degradation products that were potentially present in the pore fluids. This finding suggests that the investigated concrete admixtures (PNS, PCE, Acc) and their degradation products have no significant impact on radionuclide mobilisation.

Water Retention Characteristics and State-Dependent Mechanical and Petro-Physical Properties of a Clay Shale

A series of clay shale specimens in equilibrium with various humidity conditions were used to establish the water retention characteristics, the influence of suction on ultrasonic p-wave velocity and rock mechanical properties such as Young’s modulus, Poisson’s ratio, onset of dilatancy, unconfined compressive strength and Brazilian tensile strength. Opalinus Clay, a clay shale considered as host rock for the disposal of nuclear waste in Switzerland was utilized. The results showed that the p-wave velocity normal to bedding (vp,n) dropped sharply upon desaturation until suction approached the air-entry value. The sharp decrease was associated with desiccation cracks solely oriented parallel to bedding. For suction in excess of the air-entry value, vp,n was constant, indicating no further desiccation damage. The suction at the shrinkage limit and at the air-entry point is similar in magnitude. The p-wave velocity parallel to bedding (vp,p) remained constant in the entire range of suction investigated in this study. The constant vp,p with increasing suction might be associated with the disproportional decrease in the Poisson’s ratio and Young’s modulus and its opposing effect on p-wave velocity. An almost linear increase in unconfined compressive strength, Brazilian tensile strength, stress at the onset of dilatancy and Young’s modulus with increasing suction was observed up to a suction of 56.6 MPa. For suction larger than 56.6 MPa, relatively constant strength and stiffness was observed. The increase is associated with the net contribution of suction to strength/stiffness, which decreases nonlinearly with decreasing volumetric water content. The rate of increase in tensile strength and unconfined compressive strength with increasing suction is different depending on the rock anisotropy. Compared to the strength values (Brazilian tensile and uniaxial compressive strength) obtained from specimens loaded parallel to bedding, the tensile strength parallel to bedding and the unconfined compressive strength obtained from specimens loaded normal to bedding are considerably more affected by increasing suction or decreasing water content. The reasons for the different rates in strength increase are considered to be related to local variations in suction (i.e., local suction) as a consequence of zones of contrasting pore-size distribution. These variations may influence the effect of suction on strength, especially when the load is applied parallel to bedding and crack growth occurs predominately along bedding layers with comparably low suction.

Values in the siting of contested infrastructure: the case of repositories for nuclear waste

In major infrastructure projects, experts are usually regarded as responsible for producing and evaluating facts, whereas the public plays a role as far as values are concerned. In this study, we investigate the potential of values and value-related concepts in explaining acceptance of a deep ground repository for high-level radioactive waste in Switzerland. The study was in two parts, first, screening for relevant values using a questionnaire (N = 500) and, second, face-to-face interviews with 42 participants from the first part. Although the questionnaire could not predict overall acceptance on the basis of value concepts, interesting relative differences were nevertheless revealed between participants who were or were not affected by the potential siting of a deep geological repository in their own community. Additionally, the interviews offered insights into how values are related to the participatory process designed by the Swiss authorities.

Numerical Modelling of the Anisotropic Mechanical Behaviour of Opalinus Clay at the Laboratory-Scale Using FEM/DEM

The Opalinus Clay (OPA) is an argillaceous rock formation selected to host a deep geologic repository for high-level nuclear waste in Switzerland. It has been shown that the excavation damaged zone (EDZ) in this formation is heavily affected by the anisotropic mechanical response of the material related to the presence of bedding planes. In this context, the purpose of this study is twofold: (i) to illustrate the new developments that have been introduced into the combined finite-discrete element method (FEM/DEM) to model layered materials and (ii) to demonstrate the effectiveness of this new modelling approach in simulating the short-term mechanical response of OPA at the laboratory-scale. A transversely isotropic elastic constitutive law is implemented to account for the anisotropic elastic modulus, while a procedure to incorporate a distribution of preferentially oriented defects is devised to capture the anisotropic strength. Laboratory results of indirect tensile tests and uniaxial compression tests are used to calibrate the numerical model. Emergent strength and deformation properties, together with the simulated damage mechanisms, are shown to be in strong agreement with experimental observations. Subsequently, the calibrated model is validated by investigating the effect of confinement and the influence of the loading angle with respect to the specimen anisotropy. Simulated fracture patterns are discussed in the context of the theory of brittle rock failure and analyzed with reference to the EDZ formation mechanisms observed at the Mont Terri Underground Research Laboratory.