Passive Non-Destructive Assay based on gamma-ray spectrometry to verify UO2 samples in the form of powder and pellet

Abstract

Passive Non-Destructive Assay (PNDA) gamma-spectroscopic method is employed for nuclear material verification. The investigated materials are natural (NU) and low enriched uranium (LEU) in the form of uranium dioxide (UO2) pellets and powder, respectively. A high-resolution gamma-ray spectrometer based on HPGe detector and associated electronics is used for the measurement. The spectrometer efficiency was measured experimentally using the intrinsic self-calibration method taking into account the necessary correction factors.Sample isotopic fractions were obtained using two methods; that based on the measurement of the count rate of 185.7keV gamma line of 235U and 1001keV gamma line of 234mPa (238U) employing the intrinsic self-calibration technique to calculate the activity ratio of 235U/238U. The other method is based on uranium activity ratio measurements without efficiency corrections by choosing two gamma-rays close enough in energy, one related to 235U (84.2keV gamma line of 231Th) and the other to 238U (63.3keV gamma line of 234Th).Samples were characterized by calculating uranium isotopic mass, uranium isotopic activity ratio, total uranium content and enrichment. Special attention was given at calculating absolute error of the measured quantities, as well as the statistical behavior of the measured data in terms of the well known statistical quantities. The experimental results showed good agreement with calculated data.