Application of gamma-ray spectrometry for non-destructive determination of 235U enrichment and mass of uranium in non-irradiated VVER-type fuel pellets

Abstract

In order to determine weight fractions of 235U, 238U and 234U in VVER-type fuel pellets there were taken gamma spectra of these UO2- and (UO2-Gd12O13)- pellets using planar detector (HPLeGe) and multi-group gamma-spectra analysis code (MGAU) was used. The mass of 238U VVER-type fuel pellets was determined as a result of comparison of the count rates in gamma-peaks with Eγ = 1001 keV (the measure of 238U): in fuel pellet and in thin sample from metal uranium with known characteristics (238U mass and weight fractions of 235U, 238U and 234U). The mass of U in fuel pellets was determined on the base of the data of 238U mass (obtained by gamma-spectrometry method), weight fractions of 235U, 238U and 234U. The possibility of using scintillation spectrometer for measurement of count rates in gamma-peaks with Eγ = 1001 keV in fuel pellet and in thin U-samples was performed. The NaI(Tl) crystal Ø63*63 mm contain the wall (measurement hole Ø10*40 mm). During the measurements of gamma-spectra, the fuel pellets and thin U-samples were placed on the bottom of the wall of NaI(Tl) crystal. The identification of UO2- and (UO2-Gd2O3)- pellets was performed on the base of corresponding differences in gamma- spectrums, obtained on planar detector (presence of 43 keV KαGd-peak in (UO2-Gd2O3)- pellet gamma-spectra). The accuracy of the determination of U mass in VVER-type fuel pellets must be sufficient in order to determine the loss of U mass in (UO2-Gd2O3)- pellet (8% wt Gd2O3) with respect to U mass of UO2 pellet (Gd replace U in (UO2-Gd2O3)-pellet)