X-Ray Photoelectron Spectroscopy on Used CANDU U02 Fuel Exposed to Warm Moist -Air Conditions

Abstract

The grain-boundary chemistry of used CANDU fuel exposed to moisture- saturated air at 150 degrees C for 69 months has been investigated by X-ray Photoelectron Spectroscopy (XPS). Extensive oxidation and hydration of the UO, grain boundaries have been verified using the chemical-shift effect for the uranium and oxygen XPS peaks. The fission products cesium, barium and rubidium were detected in significant concentrations at the exposed UO, grain boundaries. Segregation of these fission products in an oxide layer with an average thickness of 0.7 nm, or 1.5 monolayers, has been demonstrated by XPS composition depth profiling and quantitative thin-film analysis.