Description: Postirradiation examinations were performed on four fuel cylinders containing UC/sub 2/ dispersed in graphite and sealed in low permeability graphite cans irradiated in the MTR. In all but one experiment, a flowing stream of He passed over the outside of the graphite cans. The estimated fuel cylinder central temperatures ranged from 2500 to 3500 deg F, and the maximum U/sup 235/ burnup was 21%. The most important radiation effects were fuel dimensional change, fission product and U migration, and microscopic structural changes. The fuel cylinders, in general, decreased in diameter and increased in lergth. The decrease in diameter was a function of fuel burnup. A 4.5% decrease in diameter was observed at a burnup of 6 x 10/sup 19/ of the fuel cylinders into the graphite cans. Fission products likewise were found throughout the walls of the graphite can, with steep concentration gradients near the inside surface of the can wall. The istopes Zr/sup 95/ and Ce/sup 144/ were more abundant near the outside wall surface than at midwall. There was no corresponding rise in the concentrations of Sr/sup 90/ and Cs/sup 137/ near the outside surface. Microstructural changes were observed in the UC/sub 2/ particles which were a function of burnup. At around 4 at.% U burnup the particles became porous and began to lose their angular shape. At 21 at.% U burnup, the particles had spheroidized and had begun to diffuse into the surrounding graphite matrix. (auth)
Date: January 1, 1963
Creator: Morgan, J.G. & Osborne, M.F.
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Partner: UNT Libraries Government Documents Department