Sang Mun Jeong

An Electrochemical Reduction of Uranium Oxide in the Advanced Spent-Fuel Conditioning Process

Abstract The Korea Atomic Energy Research Institute is currently developing the Advanced Spent-Fuel Conditioning Process (ACP) based on a pyrochemical process. An electrochemical reduction process has been developed as a key unit of the ACP. In this work, an electrochemical reduction of U3O8 powder in a LiCl-Li2O molten salt has been investigated in an electrochemical cell with a unique cathode assembly, which consists of a porous magnesia membrane, oxide powder, and a solid electricity conductor. The experimental results suggest successful demonstration of this process, exhibiting a reduction conversion of U3O8 of >99% for a batch.

AN EXPERIMENTAL STUDY ON AN ELECTROCHEMICAL REDUCTION OF AN OXIDE MIXTURE IN THE ADVANCED SPENT-FUEL CONDITIONING PROCESS

An electrochemical reduction of a mixture of metal oxides was conducted in a LiCl molten salt containing 3 wt% Li₂O at 650℃. The oxide reduction was carried out by applying a current to an electrolysis cell, and the Li₂O concentration was analyzed during each run. The concentration of Li₂O in the electrolyte bulk phase gradually decreases according to Faraday’s law due to a slow diffusion of the O₂- ions. A hindrance effect of the unreduced metal oxides was observed for the reduction of the uranium oxide. Cs, Sr, and Ba of high heat-load fission products were diffused into and accumulated in the salt phase as predicted with thermodynamic consideration.

Electrochemical properties of α -Co(OH) 2 /graphene nano-flake thin film for use as a hybrid supercapacitor

Porous nano-flake-like α-Co(OH)2 thin films were prepared by electro-deposition on graphene nanosheets (GNS) and functionalized f-GNS at 1.0 V. The functionality of hydrophilic functional groups was increased by acid treatment to enhance electrode wettability and improve the compatibility between the electrode and the electrolyte. Hydrophilic functional groups can act as anchoring sites for the precursors, enabling Co(OH)2 to more grow easily on an f-GNS electrode. The density and thickness of the α-Co(OH)2 deposition on the f-GNS electrode (13.1 μm) was greater than that on the GNS (12.3 μm) electrode. The specific discharge capacitance of the α-Co(OH)2/f-GNS electrode decreased from an initial value of 2,149mFcm−2 to 1,944 mFcm−2 over 1000 cycles, demonstrating the retention of 90% of its discharge capacitance. A hybrid capacitor was also assembled to evaluate the characteristics of a two-electrode system using α-Co(OH)2/f-GNS as the cathode. The power and energy densities of the Co(OH)2/f-GNS supercapacitor are 1,137Wkg−1 and 43Whkg−1 at 8mAcm−2, respectively.

KINETIC MODELING STUDY OF A VOLOXIDATION FOR THE PRODUCTION OF U₃O₈ POWDER FROM A UO₂ PELLET

A kinetic model for the oxidation of a UO₂ pellet to U₃O? powder has been suggested by considering the mass transfer and the diffusion of oxygen molecules. The kinetic parameters were estimated by a fitting of the experimental data. The activation energies for the chemical reaction and the product layer diffusion were calculated from the kinetic model. The oxidation conversion of a UO₂ pellet was simulated at various operating conditions. The suggested model explains the oxidation behavior of UO₂ well.

Effect of Metal (Mn, Ti) Doping on NCA Cathode Materials for Lithium Ion Batteries

NCA (LiNi0.85Co0.10Al0.05-x MxO2, M=Mn or Ti, < 0.01) cathode materials are prepared by a hydrothermal reaction at 170°C and doped with Mn and Ti to improve their electrochemical properties. The crystalline phases and morphologies of various NCA cathode materials are characterized by XRD, FE-SEM, and particle size distribution analysis. The CV, EIS, and galvanostatic charge/discharge test are employed to determine the electrochemical properties of the cathode materials. Mn and Ti doping resulted in cell volume expansion. This larger volume also improved the electrochemical properties of the cathode materials because Mn4+ and Ti4+ were introduced into the octahedral lattice space occupied by the Li-ions to expand the Li layer spacing and, thereby, improved the lithium diffusion kinetics. As a result, the NCA-Ti electrode exhibited superior performance with a high discharge capacity of 179.6 mAh g−1 after the first cycle, almost 23 mAh g−1 higher than that obtained with the undoped NCA electrode, and 166.7 mAh g−1 after 30 cycles. A good coulombic efficiency of 88.6% for the NCA-Ti electrode is observed based on calculations in the first charge and discharge capacities. In addition, the NCA-Ti cathode material exhibited the best cycling stability of 93% up to 30 cycles.