Uranium assay of fuel rods by passive gamma-ray spectrometry

The spontaneous gamma-rays characteristic of uranium isotopes can be detected and measured in order to identify the isotopic composition of uranium and to assay its total amount in various objects and materials. In order to test these methods of passive gammaray spectrometry in practice, the235U-enrichment of a known fuel rod was determined by counting 186 keV gammas from235U with Ge(Li) detectors of different volumes. The 1001 keV gammas characteristic to238U were counted too. Expected counting rates of 186 keV and 1001 keV gammas for WWER fuels are given and the suitability of passive gamma-ray spectrometry for the determination of235U-enrichment and for the assay of total uranium in reactor fuels are discussed based on these measurements.