The Swiss Federal Nuclear Safety Inspectorate (German: Eidgenössisches Nuklearsicherheitsinspektorat (ENSI)) is Switzerland's regulatory supervisory authority for nuclear safety and for the security of nuclear installations; it supervises the nuclear power plants at Beznau, Gösgen, Leibstadt and Mühleberg, the research reactors at the Paul Scherrer Institute, the University of Basel and the Swiss Federal Institute of Technology (Ecole Polytechnique Fédérale de Lausanne), as well as the Swiss national central interim storage facility for radioactive waste (ZWILAG). ENSI's headquarters are located in Brugg in the Canton of Aargau.For its part, ENSI is supervised by the ENSI Board: this body is elected by the Swiss Federal Council, to which it reports directly.
Several countries are considering argillaceous rocks as host formations for the geological disposal of radioactive waste. These rock types possess favourable properties for the retardation of radionuclide migration from the deep geological repository (DGR), including very low permeability, low molecular diffusivity, high sorption capacity and self-healing characteristics. However, several internal and external events and processes, such as excavation of the DGR, thermal loading from the waste and gas generation mechanically disturb the host rock and might adversely affect its favourable properties. The assessment of the host rock performance as a barrier to radionuclide migration necessitates the development of robust constitutive models. In the present paper, constitutive models developed by six research teams of the international DECOVALEX project are presented and compared. The models were developed using a comprehensive experimental database from laboratory tests performed on Opalinus Clay, an argillaceous host rock formation in the Swiss DGR concept. The laboratory tests consist of uniaxial compression tests, Brazilian tensile tests, and consolidated-undrained (CU) triaxial tests with pore pressure measurements, followed by microscopic observations of the deformation and failure modes. The models captured the main features of the experimental observations, including anisotropy due to bedding, deviation from linearity well before the peak strength, and localization of deformation and damage. These constitutive relations are being implemented by the teams to simulate gas migration tests in the same rock type in the dilatancy flow regime, where localized damage occurs and provides a preferential pathway for gas migration.
A new framework for generic hot channel transient CPR computations for modern BWR fuel assemblies has been developed with the goal of providing comprehensive independent safety assessments for BWR reload licensing analysis. TRAnsient Cpr analysis Tool (TRACT) is implemented in Python 3, and acts as a wrapper to calculate the critical CPR condition using TRACE as a hot channel code with initial and boundary conditions taken from upstream S3K simulations. TRACT supports subprocess-based (multi-processor) parallelism and MPI parallel execution, such that the transient CPR analyses for a typical BWR reload can be completed within minutes. Using object-oriented code design, new dryout correlations, fuel designs and even new hot channel codes can be introduced using a clean API, with minimal effort, and with little risk of breaking the existing code. The approach also makes it extremely simple to create unit tests for V&V. The V&V of TRACT is an ongoing process. While verification of the implemented correlations has been carried out, basic unit tests have been established, and selected validation has been conducted, this will be continuously extended in the future. A demonstration case has been presented to illustrate the capabilities of the code. Despite independent codes, models and methodologies, transient CPR predictions using TRACT are consistent with vendor results.
Squat reinforced concrete shear walls are commonly used as primary gravity and lateral load-resisting systems in structures. Such low aspect ratio walls respond to load in diagonal or sliding shear. A series of real-scale quasi-static cyclic shear wall tests with identical geometry were conducted at the Multi-Axial Subassemblage Testing (MAST) facility at ETH Z & uuml;rich to identify the influence of the axial load ratio and the steel reinforcement ratios on the transition between diagonal shear and sliding shear controlled behavior modes. Two specimens failed in sliding shear, and the other two failed in shear, either in diagonal compression or diagonal tension. The tests showed that squat walls exhibiting a sliding shear failure remain stable under the applied axial load even at displacements corresponding to 2% drift ratio. On the other hand, the walls that failed in diagonal shear did so in a brittle manner at displacements corresponding to 1% drift ratio. However, walls that slid had large residual displacements. The values of the shear wall axial load ratio and the longitudinal and horizontal reinforcement ratios at the transition between shear and sliding were identified.
Abstract A collection of large data sets from different orogenic belts was compiled for a correlation between organic matter (OM) versus clay mineral (CM) indices calibrated with the vitrinite reflectance, (VR) vs Kübler-Indices (KI) method. Data selection was based on a normal geothermal gradient (25 to 35 °C/km) as determined in previous studies, e.g. by maturity modelling and clay mineral reaction progress calculations. In the Lower Austroalpine (Eastern Switzerland, European Alps) a 20 myr lasting metamorphic overprint caused an OM–CM thermal equilibrium among the indices used. The observed correlation enables to determine gradual changes in metamorphic factors such as pressure, temperature and time causing sensitive shifts of the gradient slope in the range of normal gradients. For New Caledonia, an identical correlation has been determined. Prior to re-equilibration of the VR/KI indices, sediments in New Caledonia of diagenetic to incipient metamorphic grade underwent a high-pressure subduction event. VR/KI indices are in or close to equilibrium, while slight differences in OM vs CM indices allow for a better understanding of polyphase conditions, especially with respect to pressure. Temperature estimations are identical despite of their poly-phase metamorphic history, which was mainly controlled by the last orogenic thermal event lasting > 5 to < 10 myr. In the eastern Helvetic Alps and Northern Calcareous Alps similar correlations were found with slightly different slopes. Comparison between different regions is possible when using KI standardization and same data discrimination. In both parts of the Alps a complex thermal history of short durations (< 5.0 myr for the Northern Calcareous Alps to 10 myr for the Helvetic Alps) caused similar VR/KI trends, but disequilibrium is suggested by weaker regression parameters. The following correlation is calculated for a moderate geotherm (55 to 74 mWm2, mean = 61 mWm2) and normal temperature gradient conditions (25 to 35 °Ckm−1): KI = 1.134e−0.305VR, (R2 = 0.880, n = 462) with VR given as %Rmax, KI as Δ°2θ (limited to values between 0.2 to 1.0 Δ°2θ). With increasing depth (z) a VR gradient of 1.4 ± 0.2%Rmaxkm−1 is determined and a KI gradient of 0.09 ± 0.002 Δ°2θ km−1 is observed. The study illustrates that a normal geotherm can be described by VR/KI correlation, even if different heating episodes may occur. For the detection of a poly-phase or plurifacial thermal history, several indices of clay minerals and organic matter with very different kinetics should be used, as e.g. demonstrated by strong differences in smectite content at equal VR/KI values versus structural depth. A specific interest is given to the correlation of vitrinite like solid bitumen reflectance as an alternative method to VR, the persistent preservation of liptinite macerals and the stability range of clay minerals and sub-greenschist facies critical minerals compared with VR/KI data. Until now, despite the Alps in this study, systematic liptinite maceral studies have not been published in other orogenic settings.
The DECOVALEX initiative is an international research collaboration (www.decovalex.org), initiated in 1992, for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems. DECOVALEX stands for “DEvelopment of COupled Models and VALidation against EXperiments”. The creation of this international initiative was motivated by the recognition that prediction of these coupled effects is an essential part of the performance and safety assessment of geologic disposal systems for radioactive waste and spent nuclear fuel. DECOVALEX emphasizes joint analysis and comparative modeling of the complex perturbations and coupled processes in geologic repositories and how these impact long-term performance predictions. The most recent phase of the DECOVALEX Project, here referred to as DECOVALEX-2023, started in early 2020 and ended in late 2023. More than fifty research teams associated with 17 international DECOVALEX partner organizations participated in the comparative evaluation of eight modeling tasks covering a wide range of spatial and temporal scales, geological formations, and coupled processes. This Virtual Special Issue on DECOVALEX-2023 provides an in-depth overview of these collaborative research efforts and how these have advanced the state-of-the-art of understanding and modeling coupled THMC processes. While primarily focused on radioactive waste, much of the work included here has wider application to many geoengineering topics.
