Determination of Trace Uranium in Reprocessing Samples by Automatic double-curvature HOPG Pre-diffraction X-ray Fluorescence Spectrometry

As a non-destructive analysis method, X-ray fluorescence spectrometry can achieve simultaneous measurement of uranium and plutonium concentration, and is widely used in the determination of uranium and plutonium in spent fuel reprocessing technology. This method has the advantages of no sample pretreatment, fast analysis speed, and direct measurement of many elements at the same time. The original reprocessing facility used HOPG pre-diffraction EDXRF to determine uranium and plutonium in the reprocessing process samples, but the lower limit of accurate determination of uranium and plutonium concentration is only 2 mg/L, which cannot meet the measurement requirements of uranium and plutonium concentration range of 0.1-2 mg/L in the process samples, and the detection limit of uranium and plutonium aren’t greatly improved. At present, HOPG pre-diffraction X-ray fluorescence spectrometry used in the field of spent fuel reprocessing all adopt cylindrical HOPG structure, which can only show a curvature in one direction. When the point light source irradiates, the light source will converge to a radial straight line, and cannot focuse to a point, which has poor ray selectivity for specific wavelengths and high background scattering. The effective region of the crystal involved in diffraction is very small, the efficiency is very low, and the collection efficiency of X-ray photons decreases, which directly affects the detection limit and measurement accuracy of uranium and plutonium. In order to detect trace uranium in nuclear fuel reprocessing samples quickly, accurately and nondestructively, an automatic double-curvature HOPG pre-diffraction X-ray fluorescence spectrometer was developed, and an analytical method for the determination of trace uranium in simulated liquid was established. The double-curvature HOPG is added in front of the detector of the conventional energy dispersive X-ray fluorescence spectrometer, which enhances the focusing of the light source and reduces the detection limit of uranium element. The effective region of the double-curvature HOPG participating in diffraction is the arc plane corresponding to the whole region of the crystal, which is much larger than the ring diffraction region of the cylindrical graphite crystal, and can improve the focusing of the beam incident on the whole region of the crystal. The detection limit of uranium is 0.033 mg/L, the limit of quantitation is 0.110 mg/L, and the relative standard deviation of uranium concentration is better than 5%. The empirical coefficient method was used to correct the uranium element in the mixed solution containing strontium and yttrium. The recovery of uranium element was over 98%-102.3%, indicating that the method has high accuracy.