Oxidation of UO/sub 2/ at 150 to 350/sup 0/C

Conference · Thu Jan 31 23:00:00 EST 1985

OSTI ID:6044758

Gilbert, E R; White, G D; Knox, C A

Tests were performed on nonirradiated UO/sub 2/ pellets from 150 to 350/sup 0/C in atmospheric air and controlled environments and on spent light-water reactor (LWR) fuel fragments at 200 and 230/sup 0/C in atmospheric air to determine the variables that affect oxidation behavior under dry storage conditions. The weight of spent fragments increased 50 to 100 times faster than the weight of nonirradiated UO/sub 2/ pellets at 230/sup 0/C. Non-irradiated pellet fragments gained weight 5 to 7 times faster than nonirradiated pellets. The fragments simulated fuel fragmented by thermal gradients during reactor power changes. Low-density powder (U/sub 3/O/sub 8/) formed at 0.05 and 0.3% weight gain for nonirradiated pellets and fragments, respectively, but had not formed at 3% weight gain for spent fuel fragments with a burnup of 29,000 MWd/MTU. Canadian investigators had found that powder formed at intermediate levels of weight gain in CANDU spent fuel fragments with an approximate burnup of 8000 MWd/MTU. The combined effects of the high rate of weight gain in spent fuel and the burnup dependence of weight gain at powder formation resulted in a minimum in a plot of the time for the onset of powder formation versus burnup. The minimum in powder induction time occurs at or below burnup levels typical of CANDU spent fuel and spent fuel at the ends of some LWR rods. The results are described in terms of thermal and neutron irradiation-induced changes in UO/sub 2/ pellet structure and chemical composition. Other tests were performed at up to 275/sup 0/C with spent fuel fragments and nonirradiated UO/sub 2/ pellets in moist nitrogen to determine the suitability of nitrogen as a cover gas. No measurable weight gain or visible physical changes occurred during the first 2 months of testing. 22 figures, 7 tables.

• Research Organization: Pacific Northwest Labs., Richland, WA (USA)
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 6044758
• Report Number(s): PNL-SA-12632; CONF-841094-4; ON: DE85009432
• Country of Publication: United States
• Language: English

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