Optimization of laboratory-scale x-ray absorption spectroscopy (XAS) apparatus for nuclear fuel research

Dedicated to the characterization of mixed oxide nuclear fuels using x-ray absorption spectroscopy (XAS), the performance of a benchtop device was optimized. The setup is based on laboratory equipment, including a low-power x-ray tube and spherically bent crystal analyzers. By operating the device in the Johann asymmetric configuration, a significant performance enhancement is demonstrated: beam intensity increases by a factor of 3.16 at the uranium L3-edge and 1.74 at the plutonium L3-edge compared to previously reported symmetric configurations, while maintaining energy resolution between 0.6 and 2.8 eV in the 17-18 keV energy range depending on the crystal reflection used. This approach is readily extendable to other high-energy absorption edges of actinides, 4 d and rare earth metals. Using only 24 W of tube power and less than 24 h of acquisition time per sample, the device enables reliable uranium speciation. It holds promises for the speciation of plutonium as shown by x-ray absorption near edge structure spectra collected at the zirconium K-edge where Zr acted as a spectroscopic analog for Pu, with dilution limits expected to lie between 10% and 20%. Structural information can be obtained within one week of extended x-ray absorption fine structure measurements for concentrated samples. This device, named HotXAS, enables routine XAS characterization of radioactive materials in nuclear facilities, supporting future research on actinides, including the development of advanced nuclear fuels, the studies on environmental issues, and the long-term disposal of nuclear waste.