A. Goodsell, “Flat Quartz-Crystal X-ray Spectrometer for Nuclear Forensics Applications”, M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2012).
The ability to quickly and accurately quantify the plutonium (Pu) content in pressurized water reactor (PWR) spent nuclear fuel (SNF) for nuclear forensics purposes is critical. One non-destructive assay (NDA) technique being investigated to detect bulk Pu in SNF is measuring the x-ray fluorescence (XRF). Previous XRF measurements of Three Mile Island (TMI) PWR SNF taken at Oak Ridge National Laboratory (ORNL) successfully illustrated the ability to detect the 103.7 keV x ray from Pu using a planar high-purity germanium (HPGe) detector. This allows for a direct measurement of Pu in SNF. However, the underlying Compton background significantly reduced the signal-to-noise ratio for the x-ray peaks of interest thereby requiring a prolonged count time. To reduce the debilitating effects of the Compton background, a crystal x-ray spectrometer system was designed. This wavelength-dispersive spectroscopy technique isolated the Pu and U x rays according to Bragg1″s law by x-ray diffraction through a crystal structure. The higher energy background radiation was then blocked from reaching the detector using a customized collimator and shielding system. A flat quartz-crystal x-ray spectrometer system was designed specifically to fit the constraints and requirements of detecting XRF from SNF. Simulations were performed to design and optimize the collimator design and to quantify the improved signalto- noise ratio of the Pu and U x-ray peaks. In conclusion, the proposed crystal spectrometer system successfully diffracted the photon energies of interest while blocking the high energy radiation from reaching the detector and contributing to background counts. This provided a higher signal-to-noise ratio and lower percent error for the XRF peaks of interest from Pu and U.