Search

Uranium-zirconium-rare earth (U-Zr-RE) fuel slugs for a sodium-cooled fast reactor were manufactured using a modified injection casting method, and investigated with respect to their uniformity, distribution, composition, and phase behavior according to RE content. Nd, Ce, Pr, and La were chosen as four representative lanthanide elements because they are considered to be major RE components of fuel ingots after pyroprocessing. Immiscible layers were found on the top layers of the melt-residue commensurate with higher fuel slug RE content. Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) data showed that RE elements in the melt-residue were distributed uniformly throughout the fuel slugs. RE element agglomeration did not contaminate the fuel slugs but strongly affected the RE content of the slugs.

This study investigated carbon contamination in U-10wt.%Zr metallic fuel in the casting process based on the interaction between the U-Zr alloy melt and the Y2O3-plasma-spray-coated graphite. During the injection casting of U-10wt.%Zr, a ZrC reaction layer was found to form at the interface between the U-Zr melt and the Y2O3-plasma-coated graphite crucible. ZrC inclusions were also found in the matrix of the melt residue. This C contamination, evidenced by the formation of ZrC, is attributed to the migration of C through the Y2O3 coating from the graphite crucible. The results of TGA experiments using a Y2O3-plasma-coated graphite sample suggest that CO is produced by a reaction between Y2O3 and graphite at temperatures above 1773 K, which then migrates through defects in the coating to react with Zr in the U-Zr melt.

The remote injection casting process was developed using a high-capacity casting system in a mockup facility to secure the key technology for the fabrication of transmutation metallic fuels in hot cells. Seventy-eight fuel slugs fabricated simultaneously through remote injection casting were confirmed to satisfy the fabrication specification. The reaction characteristics of the coating candidates for the reusable crucible were investigated by using sessile drop tests with U-10wt%Zr-5wt%RE at 1450 °C for 1 h and LaYO3 showed the smallest interaction width. The improvement in the adhesion of Y2O3 coatings on the inner walls of the quartz mold was effective in reducing the reaction between the melt and the mold. The mechanical and chemical cleaning processes were investigated to remove the surface contamination layer of the melt residue for recycling. Both cleaning methods were effective with the mechanical treatment favored owing to the operations in hot cells. The remote injection casting process equipped with fuel loss control components developed in this work will fabricate transmutation fuels in hot cells.

We characterized the lattice parameter and phase transformation behaviors of six uranium-based metallic fuels in the temperature range 303–1173 K using in situ high-temperature X-ray diffraction (HT-XRD). In all of the fuels, α-U crystal structure almost vanished at 1023 K while UO2 crystal structure started forming at 843 K. Pawley refinement of HT-XRD data revealed anisotropic lattice thermal expansion with increases along the a- and c-axes upon annealing in all the metallic fuels. Furthermore, we confirmed that rare-earth elements (Nd, Ce, Pr, and La) contained in the U–10Zr metallic fuel hardly influenced the thermal behavior of the lattice parameters.

Mechanically bonded Al/Ni multilayers have numerous applications such as high temperature bonding and local heat sources if their stable self-propagation high temperature synthesis is controllable. In this study, stationary self-propagating reactions in Al/Ni multilayers are obtained through controlling the total layer thickness using micrometer-scale bilayer thicknesses. While stationary self-propagation is not obtained in multilayers with total layer thicknesses of 180–360 μm, it is consistently observed in multilayers with total layer thicknesses of 630–810 μm. The total layer thickness influenced the consistency of the propagation velocity of the combustion reactions in the compression-bonded Ni-sputtered Al foil multilayers. The minimum total layer thickness for a stationary propagation is identified as between 540 and 630 μm in the Al/Ni multilayers.

Compression-bonded Ni-sputtered Al foil multilayers with various atomic ratios of Al/Ni are fabricated with various bilayer thicknesses. The microstructures that are formed after the self-propagating combustion using laser ignition result in equilibrium phases in the Al/Ni binary system. Homogeneous intermetallic compounds for Al3Ni2 and AlNi are obtained for the first time in the micrometer-scale multilayers through controlling the Ni layer thickness. The onset temperatures of the multilayers are below 800 K (527 °C) for all multilayer samples. The maximum temperatures correspond to the liquidus temperatures of the intermetallic compounds. The self-propagating direction is divided into a transverse propagating direction and a gross propagating direction. The measured gross propagation velocities vary widely without exhibiting a clear trend. However, the transverse propagation velocity is dependent on the measured maximum temperatures, while the effects of the bilayer thickness are not discernible. The measured transverse propagation velocities are similar to the reported propagation velocities for sputtered multilayers with similar bilayer thicknesses.

The effects of the Al/Ni atomic ratio on the reactions of various Al/Ni multilayers are investigated. A compression-bonded Ni-sputtered Al foil multilayer process is proposed in order to study the phase formation and reaction heating in mechanically bonded multilayers. The compression-bonded multilayers exhibit advantages over the sputtered multilayers due to the negligible formation of an intermixed region and low process costs. Moreover, the process provides uniform and continuous layers that cold rolled foils cannot obtain. When the thermal annealing of Al/Ni is investigated using differential scanning calorimetry (DSC), the reaction paths differ significantly to the varying Al/Ni ratios. When the Ni/Al ratio of the multilayers was set to 3:1 and 3:2, the corresponding compounds (Al3Ni and Al3Ni2, respectively) were formed. Meanwhile, the reaction was not completed when sufficient Ni, above 40 at.%, was provided in the reaction. As the Ni atomic ratio increases from 41.2% to 57.6%, the reaction heating decreased from the theoretical values by up to 24.4%.

The organic-inorganic field effect transistors (OIFETs) with ZnS active layer were fabricated on the ITO/glass substrate using cross-linked PVP (poly-4-vinylphenol) as a gate insulator. ZnS semiconductor films were prepared by the atomic layer deposition method. In the case of cross-linked PVP film, the leakage current and capacitance were about 1× 10-8 A and 12 nF/cm2, showing good gate insulation property. The carrier concentration and mobility of ZnS film deposited on SiO2/Si wafer was found to be -9.4×1015 cm-3 and 49.0 cm2/ V·sec, respectively. For the OIFET devices with ITO/PVP/ZnS/Ti:Au structure, the carrier mobility was about 1.9 cm2/V·sec. From the AFM images, lower mobility in the OIFET device compared with ZnS film on SiO2/Si substrate may be attributed to a rough surface morphology of ZnS film.

ZnS thin films were grown by Atomic Layer Deposition (ALD) method with Diethyl- Zinc (DEZ) and hydrogen sulfide (H2S) for the application of a channel layer of OITFT (Organic-Inorganic Thin-Film Transistor). ZnS has many advantages such as high channel mobility, high deposition rate, transparency at room temperature due to the broad band gap (bandgap of ZnS : 3.7 eV), nontoxic characteristic, low resistivity, and less sensitive about oxidation than ZnO. The deposition rate of the ZnS films in our system was about 1.6 Å/cycle. ZnS film was characterized by AES, XRD, Hall-effect measurement.

The thermodynamic properties and interfacial characteristics of HfO2 thin films that were deposited by the direct plasma atomic layer deposition (DPALD) method are investigated. The as-deposited HfO2 films that were deposited by the DPALD method show crystallization of the HfO2 layers, which initiates at approximately the 35th cycle (about 2.8nm) of the DPALD process. Medium-energy ion scattering analysis reveals that the direct O2 plasma causes a compositional change in the interfacial layer as the process progresses. With an increase in the number of process cycles, the Si content decreases and the O content increases at that position, so that the HfO2-like Hf-silicate layer is formed on top of the interfacial layer. The enhanced physical reactivity of the oxygen ions in the direct plasma and the Hf-silicate layer may be the driving forces that accelerate the early crystallization of the HfO2 layer in the DPALD process in the as-deposited state.