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This project will examine inert matrix fuels containing ZrO2 and MgO as the inert matrix, with the relative amount of MgO varied from 30% to 70% in ZrO2. Reactor physics calculations will be used to examine suitable quantities of burnable poisons from the candidate elements Gd, Er, or Hf with reactor grade Pu providing the fissile component, with up to 10% of 239Pu. Ceramics will be synthesized and characterized based on the reactor physics results. The solubility of the fuel ceramics, in reactor conditions, reprocessing conditions, and repository conditions, will be investigated in a manner to provide thermodynamic data necessary for modeling.

The fuel matrix will be designed based on neutronic properties, repository behavior, and reprocessing characteristics. The matrix should be as neutron transparent as possible. Burnable poisons will be used to maintain constant reactivity. The matrix should also act as a suitable host form for fission products and actinides in a repository environment. Finally, the matrix should be compatible with reprocessing schemes under development in the advanced fuel cycle.

Work accomplished last quarter: The synthesis of the entire range of Zr to Mg, with Ce and Er concentrations being held at 5% and 2.5% respectively, has been completed with enough material for characterization and solubility studies. X-ray fluorescence has been performed on all ten batches to verify concentrations. X-ray diffraction has shown the range of Mg required for a single phase solid solution of cubic zirconia to be 10% to 28% Mg at current concentrations of Ce and Er. Pressure vessel experiments have begun. Acid dissolution studies suggest that it could be possible to leach uranium out of the ceramic without dissolving it. Therefore, these studies will be performed with uranium samples once they are prepared. The soxhlet studies have yielded quantitative data on water absorption, magnesium hydration, and corrosion of the ceramic. Calculations were performed on 3 dimensional full core neutronic modeling of MgO-ZrO2 fertile free fuel with previously selected most promising burnable poison designs.

Work performed this quarter: Optical Microscopy and SEM (scanning electron microscopy) where used to image the ceramic material. Elemental scanning by microprobe showed CeO2 to be the least soluble in the 2 ZrO2. Microprobe analysis showed the periclase phase to be pure MgO and gave stoichiometric data on the ZrO2 phase. The entire range of ZrO2 to MgO was synthesized replacing CeO2 with UO2 as the plutonium analog. XAFS (X-ray absorption fine structure) and XANES (X-ray absorption near edge spectroscopy) were performed at Argonne National Lab. Pressure vessel dissolution studies showed that although the pellet could be physically destroyed, nothing was dissolved in the water. Sulfuric acid was successful in dissolving sintered material and may therefore be a possible head-in to a reprocessing scheme. The Soxhlet apparatus shows increasing corrosion rates with increasing MgO concentration.


Ceramics; Cerium oxides; Magnesium oxide; Mixed oxide fuels (Nuclear engineering); Nuclear chemistry; Nuclear fuels; Plutonium; Solid oxide fuel cells; Zirconium oxide


Ceramic Materials | Nuclear | Nuclear Engineering | Oil, Gas, and Energy