Characterization of fuel oxidation in rods with clad-holes

Three irradiated reactor rods that had holes in the cladding were examined for oxidation. The techniques used were coulometric titration and optical examination. Coulometric titration has the capability to measure the O/M ratio for small (∼100 mg) samples. Both the longitudinal and radial directions of the rods were examined. Two of the rods had little oxidation. The third rod was oxidized everywhere, but especially at the clad-holes where the O/M values reached a maximum of 2.10. The difference between the three rods is examined. Qualitatively, optical examination revealed similar trends. For the third rod, oxidation proceeded more rapidly along the grain boundaries than within the grains themselves. Also, grain growth and gas bubble formation occurred, which had not been expected because the power levels were too low for that to occur. It seems that the temperatures were increased because of lower thermal conductivities in the higher oxide phases.