Year
2007
Abstract
The development of advanced computational algorithms for analysis of complex gamma and X-ray spectra has stimulated new investigations involving the use of nondestructive assay (NDA) based methodologies for measuring isotopic composition of nuclear materials. These new techniques provide an improved performance compared to the older analysis methodologies. Although in most cases, destructive assay (DA) techniques are the only way to achieve the desired accuracy, NDA is becoming a more frequently used alternative technique. NDA analysis can be a more simple and desirable solution for several measurement problems whenever its performance meets the imposed requirements. Since 2004 the Nuclear Energy Commission of Brazil (CNEN), in cooperation with the United States Department of Energy (US-DOE), through the Safeguards Laboratory (LASAL) and Oak Ridge National Laboratory (ORNL), respectively, has conducted several joint research activities. One of those projects is aimed to develop and implement a powerful and reliable NDA technique for isotopic and quantitative verification of uranium inventories in Brazilian bulk facilities. In Safeguards applications, desired performance for the applied measurement techniques depends on several factors (i.e. material characteristics, plant throughput, etc). In many cases use of complex DA techniques (i.e. mass spectrometry) requires substantial resources and, when applicable, an NDA option could be a more cost- and time-effective solution. Recently completed first phase of the project included hardware and software upgrades: new high-purity germanium (HPGe) detector, multi-channel analyzer (MCA), and an updated version of the multi-group analysis code – MGAU [1]. Current work includes investigation and validation of the new methodology for measuring powders and pellets enriched from 0.5 to 5% of 235U. The effects of several parameter variations (i.e. counting statistics, geometry, background level, temperature, humidity, etc.) were studied on certified reference materials. It was demonstrated that a performance of 1-1.5% rel.std. combined uncertainty (ISO-GUM compliant [2]) under laboratory conditions is achievable for the type uranium samples of interest. As a conclusion, it was demonstrated that the NDA approach is a powerful technique to be used for safeguarding nuclear materials.