In the framework of a project aiming to establish an unattended measurement station at an isotope enrichment facility, IAEA required a study to describe the state of the art of NDA methods applicable to UF6 cylinders.The objective of the present work is to provide a feasibility assessment study of all known NDA techniques applicable to the quantitative verification of all uranium categories involved in an enrichment processing plant.The quantification of the UF6 cylinders covers:-the determination of the enrichment, -the confirmation the UF6 mass ( assumed to have been previously weighted by the plant operator and independently verified by inspectors),-the assay of the UF6 homogeneity.The different hypothesis and practical constraints to be taken into account for the study requirements are [1]:- the cylinders to be considered are either 30B type ( product) or 48Y type ( feed and tail),- the enriched uranium is either from natural origin or reprocessed uranium,- the cylinders must be assayed at various temperatures,- the distance between the cylinder and the detector must be at least 50 cm to allow for safe movements of the cylinders,- the UF6 mass determination would be accurate within 10% for low enriched uranium, 15% for natural uranium and 20% for depleted uranium,- the enrichment determination must be given with a total uncertainty which does not excess:¿4.5% for low enriched uranium product,¿9.5% for natural uranium,¿18% for depleted uranium,- the measurements have to be performed in 5 minutes and in remote mode to minimize the intrusion on normal plant operator.With the objectives and assumptions as described above in mind, this document first gives an overview of the radiation properties of UF6 (chapter A) as well as some practical considerations regarding the 48Y and 30B cylinders (chapter B). The next part reviews the classical NDA methods applicable to UF6 and refers to intense measurement campaigns carried out in the years 70 -80 (chapter C), whereas the chapter D is dedicated to specific studies involving more recent techniques such as analysis of delayed neutrons and delayed photons. The most appropriate techniques will be then investigated in chapter E. The study will be based on our own results of previous measurement campaigns (235U determination with gamma detectors with germanium or LaBr3 detectors) and on MCNP simulations (passive and active neutron methods).
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