Characterization method of dielectric properties of free falling drops in a microwave processing cavity and its application in microwave internal gelation

[EN] Microwave internal gelation (MIG) is a chemical process proposed for the production of nuclear particle fuel. The internal gelation reaction is triggered by a temperature increase of aqueous droplets falling by gravity by means of non-contact microwave heating. Due to the short residence time of a solution droplet in a microwave heating cavity, a detailed knowledge of the interaction between microwaves and chemical solution (shaped in small drops) is required. This paper describes a procedure that enables the measurement of the dielectric properties of aqueous droplets that freely fall through a microwave cavity. These measurements provide the information to determine the optimal values of the parameters (such as frequency and power) that dictate the heating of such a material under microwaves.This work is a part of the PINE (Platform for Innovative Nuclear FuEls) project which targets the development of an advanced production method for Sphere-Pac fuel and is financed by the Swiss Competence Center for Energy and Mobility. The work has been also financed by the European Commission through contract no 295664 regarding the FP7 PELGRIMM Project, as well as contract no 295825 regarding the FP7-ASGARD Project. MC-S would like to thank the ITACA research team (UPV Valencia, Spain) and the EMPA Thun (Switzerland) for their support in the measurements and Carl Beard (PSI, Switzerland) for the help provided in respect with CST simulations. The work of FLP-F was supported by the Conselleria d'Educacio of the Generalitat Valenciana for economic support (BEST/2012/010).Cabanes Sempere, M.; Catalá Civera, JM.; Penaranda-Foix, FL.; Cozzo, C.; Vaucher, S.; Pouchon, MA. (2013). Characterization method of dielectric properties of free falling drops in a microwave processing cavity and its application in microwave internal gelation. Measurement Science and Technology. 24(9). https://doi.org/10.1088/0957-0233/24/9/095009S24

What we learn about bipolar disorder from large-scale neuroimaging: Findings and future directions from theENIGMABipolar Disorder Working Group

MRI‐derived brain measures offer a link between genes, the environment and behavior and have been widely studied in bipolar disorder (BD). However, many neuroimaging studies of BD have been underpowered, leading to varied results and uncertainty regarding effects. The Enhancing Neuro Imaging Genetics through Meta‐Analysis (ENIGMA) Bipolar Disorder Working Group was formed in 2012 to empower discoveries, generate consensus findings and inform future hypothesis‐driven studies of BD. Through this effort, over 150 researchers from 20 countries and 55 institutions pool data and resources to produce the largest neuroimaging studies of BD ever conducted. The ENIGMA Bipolar Disorder Working Group applies standardized processing and analysis techniques to empower large‐scale meta‐ and mega‐analyses of multimodal brain MRI and improve the replicability of studies relating brain variation to clinical and genetic data. Initial BD Working Group studies reveal widespread patterns of lower cortical thickness, subcortical volume and disrupted white matter integrity associated with BD. Findings also include mapping brain alterations of common medications like lithium, symptom patterns and clinical risk profiles and have provided further insights into the pathophysiological mechanisms of BD. Here we discuss key findings from the BD working group, its ongoing projects and future directions for large‐scale, collaborative studies of mental illness

Beyond Refugia: New insights on Quaternary climate variation and the evolution of biotic diversity in tropical South America

Haffer’s (Science 165: 131–137, 1969) Pleistocene refuge theory has provided motivation for 50 years of investigation into the connections between climate, biome dynamics, and neotropical speciation, although aspects of the orig- inal theory are not supported by subsequent studies. Recent advances in paleocli- matology suggest the need for reevaluating the role of Quaternary climate on evolutionary history in tropical South America. In addition to the many repeated large-amplitude climate changes associated with Pleistocene glacial-interglacial stages (~40 kyr and 100 kyr cyclicity), we highlight two aspects of Quaternary climate change in tropical South America: (1) an east-west precipitation dipole, induced by solar radiation changes associated with Earth’s precessional variations (~20 kyr cyclicity); and (2) periods of anomalously high precipitation that persisted for centuries-to-millennia (return frequencies ~1500 years) congruent with cold “Heinrich events” and cold Dansgaard-Oeschger “stadials” of the North Atlantic region. The spatial footprint of precipitation increase due to this North Atlantic forcing extended across almost all of tropical South America south of the equator. Combined, these three climate modes present a picture of climate change with different spatial and temporal patterns than envisioned in the original Pleistocene refuge theory. Responding to these climate changes, biomes expanded and contracted and became respectively connected and disjunct. Biome change undoubtedly influenced biotic diversification, but the nature of diversification likely was more complex than envisioned by the original Pleistocene refuge theory. In the lowlands, intermittent forest expansion and contraction led to species dispersal and subsequent isolation, promoting lineage diversification. These pulses of climate-driven biotic interchange profoundly altered the composition of regional species pools and triggered new evolutionary radiations. In the special case of the tropical Andean forests adjacent to the Amazon lowlands, new phylogenetic data provide abundant evidence for rapid biotic diversification during the Pleistocene. During warm interglacials and intersta- dials, lowland taxa dispersed upslope. Isolation in these disjunct climate refugia led to extinction for some taxa and speciation for others.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155561/1/Baker2020.pdfDescription of Baker2020.pdf : Main articl

14 - Gelation and other innovative conversion processes for aqueous-based reprocessing and recycling of spent nuclear fuels

This chapter summarizes different innovative fuel production techniques using the product streams from an aqueous reprocessing route with a focus on the well-known sol-gel conversion method. There is also reference to additional steps, post sol-gel conversion; for example, in order to load the sample matrix with minor actinides or to introduce a barrier for fission products

Determination of the critical resolved shear stress and the friction stress in austenitic stainless steels by compression of pillars extracted from single grains

The friction stress resulting from alloying elements in industrial alloys is an important strengthening mechanism. Since the preparation of single crystal from industrial material is difficult, no direct measurement of this quantity has been reported in literature. In this paper we present a new experimental method for the measurement of the Critical Resolved Shear Stress (CRSS) of single crystals cut from individual grains. It is shown that the size of the single crystal must be large enough to avoid size effects. Using transmission electron microscopy the measurement of the dislocation density allows for the decomposition of the CRSS into forest hardening and friction components. The friction stress is found to be the principal component of the materials strength. ► EBSD, MET and compression of micropillars are used to determine the micro-mechanical response. ► We present a method of measurement of the CRSS S inside individual grains of a polycrystal. ► The CRSS of a 316L-type stainless steel is decomposed into an alloy friction and forest strength. ► The alloys friction in 316L stainless steel is found much larger than forest strength.

Internal gelation at PSI. The past and the future

The Paul Scherrer Institute used to be very active in fuel fabrication R and D using the internal gelation process, which is a promising production method for spherical nuclear fuel. Such fuel kernels can be directly packed in a cylindrical cladding (a sphere-pac pin), or they can be coated in the TRISO concept. The internal gelation offers several advantages, as it is aqueous up to the forming of the sphere. Consequently, the process is almost dustless, with lower risk of incorporation. The production does not require mechanical and maintenance intensive equipment, as for example presses and grinding machines necessary for pellet type fuel. Especially for low decontaminated fuel coming from aqueous reprocessing, this offers a great advantage, because the production line can easily be handled remotely in a hot cell. In the past, many different fuel matrices were produced and tested at PSI (carbide, nitride and oxide fuels). The paper summarizes the past activities, and some important findings. Furthermore, future perspectives of this concept are shown. These are especially seen in context of Generation IV nuclear systems such as the sodium cooled fast reactor (SFR), the very high temperature reactor (VHTR), and the gas cooled fast reactor (GFR). The paper describes the former production line, which was a classical internal gelation process. Some advantages and disadvantages of this system will be illustrated which lead to a new project at PSI. A silicon oil-free system will be developed over the next years. The oil as a heat carrier is replaced by a cavity, where microwaves act on falling drops and lead to the desired gelation before the spheres drop into a washing solution. The idea of a microwave gelation has already been tested at several laboratories in the past. The paper gives an overview of these activities. Finally the concept of the new production at PSI is introduced. (author

Enhanced retention of cesium in yttria stabilised zirconia by co-implantation of iodine

The retention behaviour of fission products in the material is therefore of special importance. 1 MeV iodine and cesium ions were implanted into yttria-stabilized zirconia (YSZ) and their depth profile was measured by Rutherford Backscattering after subsequent thermal treatments. While iodine becomes significantly mobile only above approximately 1500 K, cesium already starts to move at a temperature between 1000 and 1200 K. In a sample implanted with both species significant stabilisation of cesium is observed. In this case, cesium atoms stay immobile up to 1500 K

Determination of the thermal conductivity in zirconia based inert matrix nuclear fuel by oscillating differential scanning calorimetry and laser flash

The performances of oscillating differential scanning calorimetry (ODSC) and laser-flash technique in determining the thermal conductivity and the specific heat of zirconia-based materials, analogous to a potential nuclear fuel, were compared. The tested materials were (Zr1−x−y−z,Yx,Ery,Mez)O2−(x+y)/2, with Me=Ce or Th. The measured specific heats were around 0.4 J K−1 g−1 and the thermal conductivities ranged from 2 to 3 W K−1 m−1. The ODSC measurements resulted in cp values. The thermal conductivity was derived from two complementary measurements, one with a thin and the other with a thick sample. The laser-flash technique directly delivered the thermal diffusivity of the sample; consequently, the specific heat capacity cp has to be known for determining the thermal conductivity. The ODSC measurements were affected by the position of the sample on the support. This, consequently, influenced the reproducibility of the measurements. The reproducibility of the scans by laser flash was excellent. Thermal conductivity decreased with increase in the stabilizer (Y, Er) concentration. This trend was justified on the basis of a model including concentration and size of the oxygen vacancies