Switchable Spiral Josephson junction: A superconducting spin-valve proposal

We propose a superconducting spin valve based on a Josephson junction with B20-family magnetic metal as barrier material. Our analysis shows that the states of this element can be switched by reorienting the intrinsic non-collinear magnetization of the spiral magnet. This reorientation modifies long-range spin-triplet correlations and thereby influences strongly the critical Josephson current. Compared to superconducting spin valves proposed earlier, our device has the following advantages: (i) it contains only one barrier layer, which makes it easier to fabricate and control; (ii) its ground state is stable, which prevents uncontrolled switching; (iii) it is compatible with devices of low-T Josephson electronics. This device may switch between two logical states which exhibit two different values of critical current, or its positive and negative value. I.e. 0-π switch is achievable on one simple Josephson junction.

STUDY OF STEEL BARRIER SURFACE AFTER HIGH-SPEED EXPOSURE OF W AND TIC POWDERS

The surface layer of an obstacle made of U8 steel is investigated after high-speed exposure to a flow of powder particles. After analyzing the frames of high-speed photography, the average velocities of movement of particles of tungsten and titanium carbide powders were determined. It is shown that the shock-wave loading of the barrier material and the effect of particles accelerated by the explosion energy provide a change in the physical and mechanical properties of the surface and the volume of the steel barrier material.

Titania Containing Cathodes for Lithium-Sulfur Batteries: Case Studies by Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy is used to study novel cathode materials for lithium-sulfur batteries, based on commercial carbon and titania. Coin cells with Li anode are investigated at various stages of galvanostatic cycling. For comparison, also symmetrical coin cells with a pair of positive (S/C/TiO2) or negative (Li) electrodes are studied. In addition to the application of titania as a barrier material impeding the polysulfide diffusion in the electrolyte solution, the inherent Li-insertion activity of TiO2 (anatase) and its contribution to the sulfur redox reactions is discussed.

Over 30 years of research on crushed salt as a barrier material: fundamental findings and open questions

Repositories for high-level radioactive waste in geological formations require knowledge on thermal, mechanical and fluid transport properties of the whole repository system, including the engineered barriers and backfill materials. For about 30 years, crushed salt has been considered the most suitable geotechnical barrier material to backfill cavities and encapsulate radioactive waste in rock salt repository sites (e.g., Czaikowski et al., 2020). Over time, when the surrounding cavity walls converge by the creep of salt, it can become strongly compacted and safely encapsulates radioactive waste from any fluid flow. Hence, crushed salt has been characterized in detail for its physical material properties and its response to environmental controls (stress, temperature and moisture). This characterisation provides a basis for long-term numerical simulations (e.g., Liu et al., 2018), which verify so-called safety cases in radioactive waste disposal. Displacement-controlled oedometric compaction tests mimic the long-term in situ behaviour of crushed salt. The tests show that it can be compacted to a state comprising physical rock properties similar to natural rock salt. In general, compaction is easier with an increase in humidity and temperature (e.g., Stührenberg, 2007; Kröhn, et al., 2017). Triaxial test series address the compactions' response to differing confining pressures and help to identify generalized constitutive equations for crushed salt. Both BGR procedures, the oedometric and the triaxial compaction, are verified by the German accreditation body (DAkkS). Figure 1 illustrates the history of oedometric tests at the BGR laboratory since 1993, which examined crushed salt from various origins and differing temperature conditions. Most tests focused on material from the Asse mine, revealing the compactions' response to the materials' humidity and to brine flow. Moreover, systematic test series with synthetic grain size distributions and bentonite additives provided a basis for barrier material design. More recent tests on bedded salt formations (e.g., Teutschenthal and Sondershausen mines) allow the differentiation from characteristics from domal salt deposits (e.g. Gorleben). The current research continues the history of oedometric and triaxial tests, but has a new focus on late compaction stages with marginal remaining porosities (<5 %). The approach of systematic material characterization under best-controlled conditions essentially benefits from the international research collaboration in the KOMPASS project (Czaikowski et al., 2020). The aim of its current phase two is to synthetically generate, identify and quantify dominant grain-scale deformation processes in response to changes in environmental controls. Subsequently, these laboratory results will be embedded in numerical models on the long-term in situ rheology of crushed salt.

Workshop: Best-practice for laboratory testing low-permeable materials

The testing of low-permeable materials is challenging. Yet, for the disposal of radioactive waste, it is essential, too. This workshop is aimed at gathering ambitious scientists to discuss and to collaborate on their experiences in the laboratory testing of low-permeable materials. The focus here is on the methods: What method is best for what kind of low-permeable host rock (salt/clay) and for what kind of technical barrier material (bentonite/crushed salt)? How can measurement errors be correctly determined? What are the crucial “bottlenecks” in the device setups? How can high porous but low permeable samples best be pre-saturated? How can coupled flow and cumbersome gas traps in the tests be dealt with? What is the best-practice analysis of permeability from pressure decay recordings? Is there a hope of defining a standardized procedure for low-permeability testing? These points will be reflected in the light of radioactive waste disposal and in the need to find a best-practice solution when it comes to eventual evaluation and comparison of potential underground disposal sites.