Characterization of Uranium in Bituminized Radioactive Waste Drums by Self-Induced X-Ray Fluorescence

International audienceThis paper reports the experimental qualification ofan original uranium characterization method based onfluorescence X rays induced by the spontaneous gamma emissionof bituminized radioactive waste drums. The main 661.7 keVgamma ray following the $^{137}$Cs decay produces by Comptonscattering in the bituminized matrix an intense photoncontinuum around 100 keV, i.e. in the uranium X-rayfluorescence region. “Self-induced” X-rays produced withoutusing an external source allow a quantitative assessment ofuranium as $^{137}$Cs and uranium are homogeneously mixed anddistributed in the bituminized matrix. The paper presents theexperimental qualification of the method with real waste drums,showing a detection limit well below 1 kg of uranium in 20 minacquisitions while the usual gamma rays of $^{235}$U (185.7 keV) or$^{238}$U (1001.0 keV of $^{234}$mPa in the radioactive decay chain) are notdetected. The relative uncertainty on the uranium mass assessedby self-induced X-ray fluorescence (SXRF) is about 50%, with a95% confidence level, taking into account the correction ofphoton attenuation in the waste matrix. This last indeed containshigh atomic numbers elements like uranium, but also barium, inquantities which are not known for each drum. Attenuation isestimated using a peak-to-Compton ratio to limit thecorresponding uncertainty. The SXRF uranium masses measuredin the real drums are in good agreement with long gamma-rayspectroscopy measurements (1001.0 keV peak) or withradiochemical analyse