Microchemical Studies of Irradiated Fuel by Imaging-XPS

Abstract

An advanced facility for characterization of highly radioactive materials by Imaging X-ray Photoelectron Spectroscopy (XPS) has recently been commissioned at the Chalk River Laboratories. Microchemical analysis of areas as small as 20 urn. in diameter and chemical-state imaging with a spatial resolution of ~3 um can be achieved. An auxiliary Schottky fieldemission electron gun also offers high-performance in situ capabilities for scanning electron microscopy (SEM) and scanning Auger microscopy (SAM). Based upon experience gained over the previous decade using a prototype active XPS system, the new facility has been configured to allow safe examination of irradiated-fuel samples. The pumping system and sample-preparation chambers were custom-designed to prevent internal migration or release of radioactive contamination and to allow diverse experiments under ultra-high-vacuum conditions. Preliminary results from an initial study of the fuel-sheath interface in a fuel element that was irradiated in a CANDU(l) power reactor are presented to illustrate the potential applications of the active Imaging-XPS facility. New insight into fission-product segregation and CANLUB degradation processes has already begun to emerge that should permit development of improved barrier systems on advanced CANDU fuels.