Characterization of Uranium in Bituminized Radioactive Waste Drums by Self-Induced X-Ray Fluorescence
Abstract
This paper reports the experimental qualification of
an original uranium characterization method based on
fluorescence X rays induced by the spontaneous gamma emission
of bituminized radioactive waste drums. The main 661.7 keV
gamma ray following the $^{137}$Cs decay produces by Compton
scattering in the bituminized matrix an intense photon
continuum around 100 keV, i.e. in the uranium X-ray
fluorescence region. “Self-induced” X-rays produced without
using an external source allow a quantitative assessment of
uranium as $^{137}$Cs and uranium are homogeneously mixed and
distributed in the bituminized matrix. The paper presents the
experimental qualification of the method with real waste drums,
showing a detection limit well below 1 kg of uranium in 20 min
acquisitions 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 not
detected. The relative uncertainty on the uranium mass assessed
by self-induced X-ray fluorescence (SXRF) is about 50%, with a
95% confidence level, taking into account the correction of
photon attenuation in the waste matrix. This last indeed contains
high atomic numbers elements like uranium, but also barium, in
quantities which are not known for each drum. Attenuation is
estimated using a peak-to-Compton ratio to limit the
corresponding uncertainty. The SXRF uranium masses measured
in the real drums are in good agreement with long gamma-ray
spectroscopy measurements (1001.0 keV peak) or with
radiochemical analyses
Keywords
Bituminized radioactive waste
self-induced X-ray fluorescence
Atoms
Cesium
Gamma ray spectrometers
Gamma rays
Photons
Uncertainty analysis
Uranium
Bituminized radioactive wastes
Characterization methods
Gamma-ray spectroscopy
Photon attenuation
Quantitative assessments
Radiochemical analysis
Relative uncertainty
X ray fluorescence
Radioactive wastes
Domains
Nuclear Experiment [nucl-ex]
Origin : Files produced by the author(s)
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