ULTRA HIGH ENERGY X-RAY FLUORESCENCE: A NEW PARADIGM FOR ACTINIDE CHARACTERIZATION OF SPENT FUEL

Ultra high energy X-ray fluorescence (UHEXRF) has been demonstrated as a feasible means for characterizing actinide content in spent nuclear fuel. Depleted uranium (dU) samples have been characterized using the 1-ID-C beam line of the Advanced Photon Source (APS) at Argonne National Laboratory. The dU samples included both pressed pellets of UO2 and dried spots of an aqueous uranium solution. The excitation energy was 117 keV which is above the absorption edge for the U Ka line of 115.591 keV. The XRF emission of the U Ka1 line at 98.428 keV was detected using a liquid nitrogen cooled high purity Ge detector. The samples were measured with and without a 1.3 millimeter Zircaloy shield in front of the samples which is twice the thickness of the normal fuel pin cladding. Although there was a decrease in U Ka XRF signal, sufficient intensity was obtained with as little as 5 live second dwell time resulting in several hundred counts for the smallest samples. The pressed pellets covered a concentration range from 40% to 90% dUO2 and the dried spots were 10, 5 and 1 micrograms respectively. Elemental maps showed the heterogeneity of the dried spot specimens. This also illustrates the potential of UHEXRF for through the container sub-microgram sensitivity. The significance of this achievement demonstrates the feasibility of direct actinide composition measurement through the nuclear fuel cladding. Such measurements would reduce the uncertainty obtained with passive measurements such as gamma spectroscopy and neutron counting. Although this work was done with a synchrotron, it is conceivable that this measurement could be accomplished in the laboratory using a high power x-ray tube source and appropriate x-ray optics to provide quasi-monochromatic x-rays for excitation. The demonstration of uranium detection through container walls nondestructively, offers new opportunities for applying this technology for on-line through pipe characterization, field analyses of samples and increased reliability for safeguards measurements.