Ultrahigh-Energy X-ray Fluorescence
with no sample preparation. T e calibration results indicate a detection limit of around 1 ng with Zircaloy shielding and sub-nanogram levels without the shielding. T e advantage of this direct elemental analysis approach is that it avoids the typical radiometric techniques, which must use signifi cant modeling of the measurement process to produce actual quantitative values. Such dependence on modeling corrections oſt en leads to appreciable errors resulting in accuracy issues for values that require the utmost in accuracy. UHEXRF off ers a potentially more accurate direct quantitative analysis of nuclear fuel. T e results with the SSF matrix indicate that even with nearly 50 elements present, there are no apparent elemental interfer- ences with the target elements of uranium or plutonium. T e elemental maps of the mock fuel rod provide insights into the potential that UHEXRF off ers for characterizing spent nuclear fuel. T e signifi cant aspect of this feasibility demonstration is that UHEXRF can be applied to quantifi cation of plutonium in spent nuclear fuel. T e Pu Kα line is ~103 keV. T e proximity of the Pu line to the U Kα 1 line means the quantifi cation of Pu should be straightforward, providing a new analytical method for analyzing nuclear spent fuel for both the matrix component as well as the key element for safeguards concerns. T e elemental maps of the mock fuel rod off er the following information on the nuclear fuel pellets, through Zircaloy cladding: nondestructive direct elemental measurements, uranium and thorium concentration distributions, nuclear fuel pellet homogeneity, pellet geometry, pellet orientation, and gaps between pellets. T ese are measurements that are not currently available for either fresh or spent nuclear fuel through the Zircaloy cladding. Although this demonstration used synchrotron radiation, it is feasible to construct a laboratory- based UHEXRF instrument with similar analytical capabilities. T is statement is based on work conducted by X-ray Optical Systems [ 3 ]. T ey have demonstrated construction of a UHE doubly curved crystal (DCC) optic, which would provide quasi- monochromatic radiation for excitation using a high-energy X-ray tube (~250 kV). A second DCC collection optic could be used to create a monochromatic wavelength dispersive X-ray fl uorescence (MWDXRF) instrument with high sensitivity and selectivity similar to the low-energy MWDXRF instrument we have built [ 4 ]. Although this instrument would not have the photon fl ux of the synchrotron, it would be capable of
through-the-container-wall excitation and detection of the target analyte elements even with comparable signal loss through the Zircaloy cladding.
Conclusion
In this feasibility study ultrahigh-energy X-ray fl uores- cence (UHEXRF) nondestructively characterized both model fresh and model spent nuclear fuel through the Zircaloy cladding walls. T is approach off ers distinct advantages for quantitative elemental analysis of nuclear fuel rods, including sub-nanogram sensitivity, nondestructive through-container- wall measurement capability, and direct interrogation of both fresh and spent nuclear fuel. Although this demonstration used synchrotron radiation, it is feasible to construct a laboratory-based UHEXRF instrument with similar analytical capabilities.
Acknowledgements
Use of the Advanced Photon Source, an Offi ce of Science User Facility operated for the U.S. Department of Energy (DOE) Offi ce of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. T e authors would like to acknowledge the support of the DOE NA22 Global Safeguards program for fi nancial support of this research eff ort. LA-UR 15-20152. Los Alamos National Laboratory is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.
References [1] I Nakai et al ., J Synchrotron Rad 8 ( 2001 ) 1078 – 81 . [2] GJ Havrilla et al ., “Ultra High Energy X-ray Fluorescence: A New Paradigm for Actinide Characterization of Spent Fuel,” Institute of Nuclear Materials Management 52nd Annual Meeting Proceedings , 2011,
http://inmm.org .
[3] Private communication with X-ray Optical Systems, East Greenbush, NY, Mar. 14, 2012, disclosing internal developmental research.
[4] GJ Havrilla et al ., “Monochromatic Wavelength Dispersive X-ray Fluorescence Providing Sensitive and Selective Detection of Uranium,” Institute of Nuclear Materials Management 51st Annual Meeting Proceedings , 2010,
http://inmm.org .
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