Microchemical Analysis of the Fuel-Sheath Interface in a Power-Ramped CANDU Fuel by Imaging-XPS

Abstract

A detailed study of the microchemistry at the fuel-sheath interface in an intact outer element from a power-ramped CANDU fuel bundle has been conducted by imaging X-ray photoelectron spectroscopy (XPS). The power ramp caused several other elements in this bundle to fail by stress-corrosion cracking. An abundance of fission products, especially cesium, was found on all sheath and end-cap surfaces, and a number of segregated impurities, most notably sodium, were also identified. These findings suggest that iodine may not be the sole causative agent for stress-corrosion cracking of Zircaloy fuel sheath. The CANLUB layer was partly retained on the sheath and partly on the fuel pellets-different regions could be identified for microchemical XPS analysis by in situ scanning electron microscopy (SEM).