Year
1997
Abstract
An algorithm was developed to determine the calibration parameters for a proposed Method of Inventory Verification in a Diffusion Enrichment Cascade. The method is based on the correlation between the count produced in a NaI(Tl) detector by the 185.7 keV gamma rays (U-235) and its mass in a diffuser. The algorithm embodies two computer programs: the first one, calculates the detector efficiencies for point sources distributed over the diffuser. The second program, fed with these efficiencies, performs an integration over 5 dimensions - 3 spatial and 2 for uranium mass and enrichment - producing a family of curves expressing the count rate at the detector against the mass of U-235 for each enrichment. The results show that the uranium mass and enrichment affect substantially the count rate, precluding the using of a simple calibration factor to transform that count rate into mass of U-235. To simplify the using of the algorithm by the inspectors, that family of curves was condensed in one single function, expressing the ratio count rate/enrichment versus mass of uranium, from which, the mass of U-235 can be deduced. A fair agreement with the Operator’s declared values was obtained by applying this algorithm to experimentally measured count rates.