Tsuyoshi Usami

Pyrochemical reduction of uranium dioxide and plutonium dioxide by lithium metal

Abstract The lithium reduction process has been developed to apply a pyrochemical recycle process for oxide fuels. This process uses lithium metal as a reductant to convert oxides of actinide elements to metal. Lithium oxide generated in the reduction would be dissolved in a molten lithium chloride bath to enhance reduction. In this work, the solubility of Li 2 O in LiCl was measured to be 8.8 wt% at 650 °C. Uranium dioxide was reduced by Li with no intermediate products and formed porous metal. Plutonium dioxide including 3% of americium dioxide was also reduced and formed molten metal. Reduction of PuO 2 to metal also occurred even when the concentration of lithium oxide was just under saturation. This result indicates that the reduction proceeds more easily than the prediction based on the Gibbs free energy of formation. Americium dioxide was also reduced at 1.8 wt% lithium oxide, but was hardly reduced at 8.8 wt%.

Lithium reduction of americium dioxide to generate americium metal

The lithium reduction process has been developed for application to a pyrochemical recycle process for oxide fuels. This process uses lithium metal as a reductant to convert oxides of actinide elements to metal. Lithium oxide generated as a product of the reduction would be dissolved in a molten lithium chloride bath to enhance reduction. In this work, the reduction of americium dioxide to its metal was experimentally confirmed. At the end of the reduction, more than 99.9% of the Am was recovered from the salt phase to a solid Am phase. It was also shown that the lithium oxide concentration in lithium chloride is required to be kept under 5.1 wt%. When the concentration of lithium oxide was between 5.1 and 6.3 wt%, americium formed monoxide.

Recovery of U-Pu Alloy from MOX Using a Pyroprocess Series

Abstract A series test of the pyroprocess was carried out to recover U-Pu alloy from mixed oxide (MOX) pellets. In the Li-reduction step, the reduction behavior of MOX was similar to that of UO2. In the electrorefining step, the separation factor between U and Pu was 1.9 for the combination of the reduced MOX anode and the liquid cadmium cathode, which agrees well with the value obtained in previous studies. Approximately 99% of the HM (U and Pu) initially present in the anode or molten salt was detected in the electrodes or molten salt after the electrolysis. Considering the analytical error of inductively coupled plasma-atomic emission spectroscopy, this mass balance is reasonable. The amount of U remaining in the anode was slightly larger than that of Pu, due to the reoxidation. The U-Pu alloy ingot was successfully formed by distillation of Cd.

Integrated Experiments of Electrometallurgical Pyroprocessing Using Plutonium Oxide

Electrometallurgical pyroprocessing is a promising technology to realize actinide fuel cycle. Integrated experiments to demonstrate electrometallurgical pyroprocessing of PuO2 in continuous operation were carried out. In each test, 10–20 g of PuO2 was reacted with Li reductant to form metal product. The reduction products were charged in an anode basket of the electrorefiner with LiCl-KCl-UCl3 electrolyte. Using the anode, deposition of uranium on the solid cathode was carried out when PuCl3/UCl3 concentration ratio was low. After the Pu/U ratio in the salt electrolyte was increased enough, Pu and U were recovered simultaneously on a liquid cadmium cathode. By heating up the deposits for distillation of the salt and the cadmium, U metal or Pu-U alloyed metal was obtained as residues in the crucible. It was the first result to demonstrate the recovery of metal actinides in the continuous operation of pyroprocessing of oxide fuels.

Lithium reduction of a MOX pellet

Abstract The MOX pellet of approximately 10g was reduced with lithium metal in molten lithium chloride at 923K. The pellet has high density and consists of 90% of uranium, 10% of plutonium, and 0.2% of americium growing in from plutonium. No major fracturing of the pellet occurred during reaction. Uranium and plutonium were essentially completely reduced to metal with no significant change in the ratio between them. Most of the lithium oxide generated by the reaction dissolved in the molten salt. SEM observation clearly showed a lot of pores and cracks in the reacted pellet. The generation of the apertures was caused by significant decrease of molar volume from oxide to metal. Plutonium and americium were detected in the samples taken from the molten salt during the experiment. Approximately 5% of initial load of plutonium and 75% of americium eluded from the pellet and most of them precipitated on the bottom of the crucible in end of the experiment.

Chemical Reduction of SIM MOX in Molten Lithium Chloride Using Lithium Metal Reductant

A simulated spent oxide fuel in a sintered pellet form, which contained the twelve elements U, Pu, Am, Np, Cm, Ce, Nd, Sm, Ba, Zr,Mo, and Pd, was reduced with Li metal in a molten LiCl bath at 923 K. More than 90% of U and Pu were reduced to metal to form a porous alloy without significant change in the Pu/U ratio. Small fractions of Pu were also combined with Pd to form stable alloys. In the gap of the porous U-Pu alloy, the aggregation of the rare-earth (RE) oxide was observed. Some amount of the RE elements and the actinoides leached from the pellet. The leaching ratio of Am to the initially loaded amount was only several percent, which was far from about 80% obtained in the previous ones on simple MOX including U, Pu, and Am. The difference suggests that a large part of Am existed in the RE oxide rather than in the U-Pu alloy. The detection of the RE elements and actinoides in the molten LiCl bath seemed to indicate that they dissolved into the molten LiCl bath containing the oxide ion, which is the by-product of the reduction, as solubility of RE elements was measured in the molten LiCl-Li2O previously.