59 research outputs found
Micro/Nano-Structural Examination and Fission Product Identification in Neutron Irradiated AGR-1 TRISO Fuel
Advanced electron microscopic and micro-analysis techniques were developed and applied to study irradiation effects and fission-product behavior in selected low-enriched uranium-oxide/uranium-carbide tristructural-isotropic (TRISO)-coated particles from fuel compacts in four capsules irradiated to burnups of 11.2 to 19.6% fissions per initial metal atom (FIMA) consisting of Baseline, Variant 1, and Variant 3 fuel types. Trend analysis shows precipitates were mostly random in their distribution along the perimeter of the inner pyrolytic carbon-silicon carbide (IPyC-SiC) interlayer with only weak association with kernel protrusion and buffer fractures. Pd is dominantly found in most precipitates in both intra and intergranular locations. Nano-sized Ag is predominantly found in grain boundaries and triple points with only two findings of Ag inside a SiC grain in two different compacts (Baseline and Variant 3 fueled compacts). Generally, more element combinations exist for precipitates from particles with relatively low Ag retention compared to particles with relatively high Ag-retention irrespective of fuel type. This study shows the presence of Cs in particles from all compacts evaluated. From this work, no single fission product mechanism hypothesis can be reported. The complexity of mechanisms is further highlighted by the multiple variations of elemental combinations found in the more than 700 fission product precipitates examined. It seems that movement of Ag is not assisted by a specific element in all cases. Therefore, it is not necessarily true that a chemical-assisted transport mechanism is dominant. The presence of Ag predominantly on grain boundaries suggests that a grain boundary transport mechanism may be prominent. Studies to determine the effect of neutron damage are recommended for future work
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Magnetic field and field orientation dependence of the critical current density in Bi-2212 round wires and other HTS conductors
The authors have performed measurements of the magnetic field dependence of the critical current density J{sub c} of Bi-2212/Ag round wire produced by isothermal melt processing. In contrast to the case for flat tape, there is very little dependence of J{sub c} on the direction of the magnetic field as it is rotated normal to the wire axis, which is the direction of the nominal current flow. However, when the angle of the magnetic field direction is rotated from normal to the wire axis to parallel to that axis, J{sub c} at 64 K and 0.2 T increases by more than a factor of four. Again, this is in contrast to the results observed for Bi-2212/Ag and Bi-2223/Ag flat tapes, which show no anisotropy under similar experimental conditions. They can explain these differences in angular anisotropy by referring to the microstructure of these two conductor types, which have distinctly different types of grain alignment. They discuss the general behavior of the dependence of J{sub c} on the orientation of a magnetic field for high temperature superconductors
Through-thickness superconducting and normal-state transport properties revealed by thinning of thick film ex situ YBa2Cu3O7-x coated conductors
A rapid decrease in the critical current density (Jc) of YBa2Cu3O7-x (YBCO)
films with increasing film thickness has been observed for multiple YBCO growth
processes. While such behavior is predicted from 2D collective pinning models
under certain assumptions, empirical observations of the thickness dependence
of Jc are believed to be largely processing dependent at present. To
investigate this behavior in ex situ YBCO films, 2.0 and 2.9 um thick YBCO
films on ion beam assisted deposition (IBAD) - yttria stabilized zirconia (YSZ)
substrates were thinned and repeatedly measured for rho(T) and Jc(H). The 2.9
um film exhibited a constant Jc(77K,SF) through thickness of ~1 MA/cm2 while
the 2.0 um film exhibited an increase in Jc(77K,SF) as it was thinned. Neither
film offered evidence of significant dead layers, suggesting that further
increases in critical current can be obtained by growing thicker YBCO layers.Comment: To appear in Applied Physics Letter
Properties of recent IBAD-MOCVD Coated Conductors relevant to their high field, low temperature magnet use
BaZrO3 (BZO) nanorods are now incorporated into production IBAD-MOCVD coated
conductors. Here we compare several examples of both BZO-free and
BZO-containing coated conductors using critical current (Ic) characterizations
at 4.2 K over their full angular range up to fields of 31 T. We find that BZO
nanorods do not produce any c-axis distortion of the critical current density
Jc(theta) curve at 4.2 K at any field, but also that pinning is nevertheless
strongly enhanced compared to the non-BZO conductors. We also find that the
tendency of the ab-plane Jc(theta) peak to become cusp-like is moderated by BZO
and we define a new figure of merit that may be helpful for magnet design - the
OADI (Off-Axis Double Ic), which clearly shows that BZO broadens the ab-plane
peak and thus raises Jc 5-30{\deg} away from the tape plane, where the most
critical approach to Ic occurs in many coil designs. We describe some
experimental procedures that may make critical current Ic tests of these very
high current tapes more tractable at 4.2 K, where Ic exceeds 1000 A even for 4
mm wide tape with only 1 micron thickness of superconductor. A positive
conclusion is that BZO is very beneficial for the Jc characteristics at 4.2 K,
just as it is at higher temperatures, where the correlated c-axis pinning
effects of the nanorods are much more obvious
High-temperature change of the creep rate in YBa 2Cu 3O 7-δ films with different pinning landscapes
Magnetic relaxation measurements in YBa 2Cu 3O 7-δ (YBCO) films at intermediate and high temperatures show that the collective vortex creep based on the elastic motion of the vortex lattice has a crossover to fast creep that significantly reduces the superconducting critical current density (J c). This crossover occurs at temperatures much lower than the irreversibility field line. We study the influence of different kinds of crystalline defects, such as nanorods, twin boundaries, and nanoparticles, on the high-temperature vortex phase diagram of YBCO films. We found that the magnetization relaxation data is a fundamental tool to understand the pinning at high temperatures. The results indicate that high J c values are directly associated with small creep rates. Based on the analysis of the depinning temperature in films with columnar defects, our results indicate that the size of the defects is the relevant parameter that determines thermal depinning at high temperatures. Also, the extension of the collective creep regime depends on the density of the pinning centers.Fil: Haberkorn, Nestor Fabian. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Patagonia Norte; ArgentinaFil: Miura, M.. No especifĂca;Fil: Baca, J.. No especifĂca;Fil: Maiorov, B.. No especifĂca;Fil: Usov, I.. No especifĂca;Fil: Dowden, P.. No especifĂca;Fil: Foltyn, S. R.. No especifĂca;Fil: Holesinger, T. G.. No especifĂca;Fil: Willis, J. O.. No especifĂca;Fil: Marken, K. R.. No especifĂca;Fil: Izumi, T.. No especifĂca;Fil: Shiohara, Y.. No especifĂca;Fil: Civale, L.. No especifĂca
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The early stages of microstructural development of the colony structure in Bi-2223 tapes.
The current protocol for processing (Bi,Pb)2Sr2Ca2Cu3010-(B i-2223) multifilamentary tapes involves the in situ formation of the primary phase from a suitable mixture of precursor phases. As such, the developments during the first few minutes of heat treatment determine to a large extent the efficiency of primary phase development, competing secondary phase development, texture evolution, and grain-to-grain connectivity. This work documents the development of the liquid phase, secondary phases, defects which may affect alignment and reaction kinetics, and the precipitation of Bi-2223 from the liquid phase
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INVESTIGATION OF THE INITIAL STAGES OF PROCESSING BI-2223 MULTIFILAMENTARY TAPES BY ANALYTICAL ELECTRON MICROSCOPY
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