A comparison study on the burnup of HTR-10 fuels using radiometric and mass spectrometric methods

Online burnup measurement of a single irradiated spherical fuel element using gamma spectrometry has been applied for years on HTR-10. This reactor has a complex operation history for varies experiments, which raises the uncertainty over the non-destructive measured burnup. In this research, three irradiated spherical fuel elements with different burnup were deconsolidated, and their coated particles were analysed by both radiometric methods based on Cs-137 activity and mass spectrometric methods based on neodymium and actinide mass. The burnup distribution in each spherical fuel element was indicated by fractional U-235 burnup of particles from various radii and relatively uniform. The inventory of Cs-137 in one spherical fuel element was measured by on- and off-line gamma spectrometry and results showed tiny differences. Destructively measured Cs-137 activities from particles indicate negligible portion of Cs-137 in the graphite matrix. Burnup calculated from Cs-137 by radiometric method and Nd-148 by mass spectrometric method were compared. Results showed that the two values were not significantly different for fuels with a clear radiation history, but differences were observed in the fuel with a complex radiation history.