Ultra High Energy X-ray Fluorescence Application to Characterization of Nuclear Fuel

Ultra-high energy X-ray fluorescence (UHEXRF) is used to characterize a mock nuclear fuel rod. The mock fuel rod is a standard 600 micrometer thick Zircaloy alloy tube only 25 mm long. The 6 mock fuel pellets (8 mm in diameter by 2 mm thick) consist of a thorium oxide base with varying amounts of depleted uranium oxide from less than 1 wt% to over 3 wt%, sealed inside the Zircaloy tube. The pellets were pressed with stearic acid as a binder. The thorium-uranium mixture provides a convenient model for the uranium-plutonium heavy metal ratio of actual spent fuel. The mock fuel rod was scanned along the length of the rod with an excitation beam from the 1-ID-C beam line of the Advanced Photon Source (APS) at the Argonne National Laboratory. The excitation energy was 117 keV which is above the absorption edge for the U Ka line. The XRF emission of the U Ka1 line at 98.428 keV was detected using a liquid nitrogen cooled high purity Ge detector. The excitation spot size was around 50 x 250 micrometers. A plot of the uranium Ka line as a function of position along the mock fuel rod shows changes in uranium composition both within the mock fuel pellets and between the fuel pellets, tracking the different uranium compositions. The line scan demonstrates a clear measure of the uranium concentration within the mock fuel pellets through the Zircaloy tubing. The interface between 2 of the mock fuel pellets was mapped, collecting XRF spectra covering a slice that was around 1 x 10 mm, with a 50 x 50 micrometer excitation spot. The mapping effort not only shows the differences in uranium concentration, but it also provides a picture of the pellet shapes along with the gap distance between the pellets. UHEXRF has significant potential for characterization of both fresh and spent nuclear fuel. Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357