Oxidation of CANDU uranium oxide fuel by air in gamma radiation at 150 degrees C

Oxidation of CANDU nuclear fuel (UO2), heated at 150 degrees C in air, in O-2 with 60% saturated steam, and in Ar with 60% saturated steam atmospheres for similar to 2 years in gamma fields of dose rate similar to 15 Gy h(-1), was investigated using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. Surface analysis of UO2 disks shows formation of U3O8 on the UO2 disks exposed to air or O-2. This is the first observation of the formation of U3O8 on UO2 by air oxidation at such a low temperature. The rate of U(3)O( )8 formation by dry air oxidation of UO2 at 150 degrees C is very low. The presence of water vapor along with O-2 increases the oxidation of UO2 in gamma fields, leading to the formation of U6+ phases, e.g., UO3 . H2O along with U3O8. UO2 did not suffer any oxidation by water vapor radiolysis at 150 degrees C in an O-2-free atmosphere.