Characterization of Dissolved High-Burnup Nuclear Fuel with Microcalorimeter, HighPurity Germanium, and Cadmium Zinc Telluride Gamma Spectrosc

Nondestructive characterization of high-burnup nuclear fuels is an important potential application of gamma spectroscopy and enabling technology for advanced reactors and fuel cycle facilities. While this is a challenging measurement due to the complexity of the gamma spectrum and severe Compton scattering background from intense fission product activity, new technologies such as microcalorimeter gamma spectrometers may be able to access additional signatures of fuel composition. To evaluate the potential of advanced and traditional gamma spectroscopy in characterizing spent fuel composition, burnup, and cooling time we conducted a series of measurements on dissolved high-burnup light water reactor fuels using microcalorimeter, high-purity germanium, and cadmium zinc telluride detectors. In particular, microcalorimeter and high-purity germanium detectors were found to be complementary in that each provide the best available energy resolution in low- and high-energy regions of the spectrum respectively. In the low-energy part of the spectrum below 200 keV, we find that additional burnup and cooling time indicators are available with microcalorimetry beyond the traditional 134Cs/137Cs ratio. 243Am/241Am is most sensitive to burnup and 155Eu/154Eu is sensitive to both cooling time and burnup. These ratios may provide more robust analysis of burnup and cooling time especially in combination with the 134Cs/137Cs ratio from a germanium detector. We will present results from this study and discuss implications for safeguards and material accounting in advanced reactors and nuclear fuel cycle facilities.