Ultrahigh-Energy X-ray Fluorescence
Figure 4 : Uranium elemental intensity map of a dried spot deposit of a 1 μ L synthetic spent fuel matrix solution containing 99 ng U.
Figure 6 : Picture of mock fuel rodlet covered in Kapton fi lm, which contains 8 mock fuel pellets. The red line indicates one line scan of multiple line scans used to acquire elemental maps shown in Figure 7 for the 25 mm long by 8 mm diameter rodlet.
Figure 5 : Calibration log-log plot of known uranium mass with measured integrated uranium intensity from elemental maps of dried spot deposits with different matrices, which includes aqueous and synthetic spent fuel. Correlation coeffi cient for both matrices is 0.974.
nuclear fuel rod is demonstrated by scanning the mock fuel rod prepared with 8 mock fuel pellets. A picture of the mock fuel rod is shown in Figure 6 . T e mock fuel rod is shown with the Kapton fi lm used to encapsulate all samples containing radioactive materials to ensure no contamination of the experimental facilities is possible. T e red line on the picture indicates one of the successive line scans that were done to create elemental maps of the thorium and uranium inside the Zircaloy tube. In this case the Zircaloy is a nominal 600 µm thick, which is typical of nuclear fuel rods. Figure 7 shows an illustration of the mock fuel rod and the mock fuel pellets inside the Zircaloy tube. T e numbers on the uranium doped pellets are the concentration of the uranium oxide mixed with the thorium oxide. T e thorium (upper) and uranium (lower) elemental maps obtained through the Zircaloy cladding are shown below the cartoon. T e elemental images provide
2015 May •
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Figure 7 : Cartoon of mock fuel pellets within mock fuel rod (top) with the values of the uranium oxide composition indicated in wt%. The elemental maps of the thorium matrix (middle) and uranium analyte (bottom) distribution acquired through the 600 µm thick Zircaloy wall. The X-ray spot size was 100 µm, and step size was 100 µm.
several levels of information besides the spatial distribution of thorium and uranium. Fundamentally, the elemental maps indicate the heterogeneity of the matrix in these pellets. In real nuclear fuel the spatial distribution of the fuel element matrix should be uniform. T e elemental maps show the shape of the pellets as well as spacing between the pellets. T e elemental concentration of the uranium, which is the plutonium surrogate, demonstrates detection well below the nominal 1 wt% of Pu in real spent nuclear fuel.
Discussion T e results presented off er a new approach for elemental determination of spent nuclear fuel in a nondestructive manner
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