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Current flow sheets for processing used nuclear fuels do not produce separated streams of all of the actinides. These aqueous processing streams must be converted into solid forms suitable for recycle (fuel/target fabrication), storage, or disposal, necessitating co-conversion. A process developed at ORNL in the 1980s to make UO{sub 3} suitable as fuel feedstock was studied for preparation of mixed actinide oxides with similarly favorable ceramic properties. The process, Modified Direct Denitration (MDD), uses ammonium nitrate to alter the thermal decomposition behavior of metal nitrates and improve the ceramic properties of the resulting solid oxide. Since plutonium (IV) and neptunium(IV) form compounds similar to uranium with the ammonium ion [(NH{sub 4}){sub 2}Pu(NO{sub 3}){sub 6}, (NH{sub 4}){sub 2}Np(NO{sub 3}){sub 6}], MDD-conversion of these metals was considered to be applicable. Co-conversion has advantages for making mixed oxides over individual element conversions that are followed by dry mixing of the oxide powders. Issues associated with preparing a mixture from individual oxides include use of additional equipment, dusting associated with feeding and milling, time requirements for milling, blending to obtain a uniform mixture, and inhomogenity at higher plutonium concentrations. These issues can be partially or wholly avoided by using MDD coconversion in which the mixing of the individual metals occurs in liquid solution; thus, adjusting relative metal concentrations is simpler and the resulting mixed oxide is more uniform than that produced by blending the individual oxides. Utilizing MDD also eliminates the need for mechanical treatment of the powder to obtain the desired ceramic properties, such as surface area and particle size distribution, since these characteristics are acceptable as-produced. The original MDD development work established that uranium oxide with good ceramic properties could be made. Following the discovery, a more fundamental understanding of the chemistry of the uranium-ammonium double nitrate salt was developed. Later pilot-scale studies produced kilogram quantities of UO{sub 3} using engineering-scale (1 kg/hour), continuously-operated equipment, while establishing the reliability of the process and equipment. The current work was performed in support of the Advanced Fuel Cycle Initiative (AFCI), utilizing glove-box-contained equipment (100 g/hour) to produce UO{sub 3}, PuO{sub 2}, and mixed oxides of uranium, plutonium, neptunium, and americium from a nitrate solution of those actinides. Then the MDD glove-box system was utilized in the Coupled-End-To-End (CETE) project to convert the U-Pu-Np and uranium product solutions into oxide powders. As part of the CETE project, a powder characterization laboratory was established in gloveboxes with instruments required for the determination of: (1) surface area by the BET methodology; (2) tap density by using a Quantachrome AutoTap; (3) flow properties by using a Freeman technology powder rheometer; (4) material composition and crystalline structure by using a powder X-ray diffractometer; (5) particle size distribution by using a laser light-scattering analyzer; and (6) imaging of the powders with a stereomicroscope. These instruments can be used to characterize the products and to determine the effects of MDD operating parameters on product powder morphology. Ultimately, the powder characteristics necessary to produce high-density, sintered MOX pellets can be determined

MDD Status Letter Report (AFCI CETE Milestone)