Microstructure of irradiated uranium dioxide

Sintered UO₂ pellets irradiated at high temperature to a burnup of 2,700 MWD/T-UO₂ were studied by replica electron microscopy. The as-irradiated pellet surfaces were covered by a thin layer easily soluble in dilute acid. This layer apparently was deposited as a sublimate during irradiation. The etched surfaces of the irradiated specimens were uniformly dispersed with flat circular domes about 1 μ in diameter, constituted of precipitates resistant to etching solution, apparently a mixture of fission products and UO₂. On the surface of each dome were several 'sprout' precipitates 0.1 to 0.3 μ in diameter, and almost immune to chemical etchant. (author)