Determination of 235U Isotopic Abundance of U Samples by a NDA Based Method to Enhance Capability of a National Safeguards System

In order to investigate some non-destructive techniques to determine the isotopic abundance of uranium oxide samples for quantitative verification of flow, inventories and balances of material in bulk facilities, the Safeguards Laboratory (LASAL) of the Brazilian Nuclear Energy Commission (CNEN) and the United States Department of Energy (US-DOE), supported by experts from Oak Ridge National Laboratory (ORNL) and Portsmouth Gaseous Diffusion Plant have established a technical cooperation project. Part of this project refers to studies and tests based on gamma and X-ray measurements with a high purity germanium detector (HPGe) with data analysis through a multi-group analysis code – MGAU® [1]. Typical accuracies of 1-2% [2] are expected for a single measurement of only a few minutes of counting time for uranium samples in equilibrium with their daughter products, not containing Pu and other radionuclides and with container wall thickness of less than about 10 mm steel. In a laboratory environment, additional investigations are being conducted under a very low background level and using different counting times, geometries and material characteristics in order to meet a performance of 0.5-1% for isotopic abundances over the range from 0.5 to 5% 235U. Previous evaluations demonstrated that this performance would satisfy the safeguards requirements for an effective and efficient verification of inventories and balances of nuclear material in Brazilian bulk facilities by the national inspectorate.