The primary objective of the present study is to identity the most promising, viable technologies that are likely to culminate in an expedited development of the next-generation, field-deployable instrument for providing rapid, accurate, and precise enrichment assay of uranium hexafluoride (UF 6 ). UF 6 is typically involved, and is arguably the most important uranium compound, in uranium enrichment processes. As the first line of defense against proliferation, accurate analytical techniques to determine the uranium isotopic distribution in UF 6 are critical for materials verification, accounting, and safeguards at enrichment plants. As nuclear fuel cycle technology becomes more prevalent around the world, international nuclear safeguards and interest in UF 6 enrichment assay has been growing.At present, laboratory-based mass spectrometry (MS), which offers the highest attainable analytical accuracy and precision, is the technique of choice for the analysis of stable and longlived isotopes. Currently, the International Atomic Energy Agency (IAEA) monitors the production of enriched UF 6 at declared facilities by collecting a small amount (between 1 to 10 g) of gaseous UF 6 into a sample bottle, which is then shipped under chain of custody to a central laboratory (IAEA's Nuclear Materials Analysis Laboratory) for high-precision isotopic assay by MS. The logistics are cumbersome and new shipping regulations are making it more difficult to transport UF 6 . Furthermore, the analysis is costly, and results are not available for some time after sample collection. Hence, the IAEA is challenged to develop effective safeguards approaches at enrichment plants. In-field isotopic analysis of UF 6 has the potential to substantially reduce the time, logistics and expense of sample handling. However, current laboratory-based MS techniques require too much infrastructure and operator expertise for field deployment and operation. As outlined in the IAEA Department of Safeguards Long-Term R&D Plan, 2012-2023, one of the IAEA long-term R&D needs is to "develop tools and techniques to enable timely, potentially real-time, detection of HEU (Highly Enriched Uranium) production in LEU (Lowly Enriched Uranium) enrichment facilities" (Milestone 5.2). iv measurements that do not require the stated high accuracy or precision of the ITVs to which it was compared).The list presented below summarizes the outcome of the present study, and groups all reviewed techniques into "recommended", "promising", or "not recommended"; the "benchmark" techniques are also included and labeled as such. The list is presented in a highly abridged way such that only the final recommendations are given. The performance of a technique in the seven evaluation metrics and its ranking are summarized in Table 6.1, whereas short discussion and comments on the recommendation can be found in Section 6.2 of this report. Furthermore, comprehensive and in-depth reviews on the scientific principle of each technique, its instrument option, its limitations and main gaps betwe...