Light water reactor fuel reprocessing: dissolution studies of voloxidized fuel

Voloxidation is a proposed head-end process to remove tritium from irradiated LWR fuel by roasting the fuel in the presence of oxygen. The process oxidizes UO/sub 2/ to a fine U/sub 3/O/sub 8/ powder with high surface area for dissolution. Small-scale tests with irradiated Robinson, Oconee, and Saxton reactor fuels have been made to determine the dissolution behavior of both voloxidized and nonvoloxidized (UO/sub 2/) fuel. No significant technical problems were encountered in batch-dissolving of the U/sub 3/O/sub 8/ or UO/sub 2/ fuel. Dissolution rates were well-controlled in all tests. Significant observations from U/sub 3/O/sub 8/ dissolution, when compared to UO/sub 2/ dissolution, included: (1) reduced tritium and ruthenium (/sup 106/Ru) concentration in dissolver solutions, (2) increased weight of insoluble noble metal fission product residue (approximately 2.2X greater), and (3) increased fraction of the total plutonium which remains insoluble and is collected with the fission product residue. The insoluble plutonium was leached easily from the residue by 10M HNO/sub 3/ to ensure quantitative plutonium recovery. The weight of the fission product residue collected from both U/sub 3/O/sub 8/ and UO/sub 2/ fuels increased linearly with fuel burnup. A major fraction (> 88%) of the /sup 85/Kr was evolved from U/sub 3/O/sub 8/ fuel during dissolution rather than voloxidation. The /sup 85/Kr evolution rate was an appropriate monitor of fuel dissolution rate. Virtually all of the /sup 129/I was evolved by air sparging of the dissolver solution during dissolution