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In the Unattended Cylinder Verification Station (UCVS) project, a field trial in 2019 at a fuel fabrication facility resulted in a direct comparison of several gamma-ray detectors and methods for Type 30B UF6 cylinder enrichment assay. The field trial included measurements of 268 unique cylinders that ranged in enrichments (depleted uranium to 4.95 wt.% 235U) and other factors to assess enrichment assay performance. The detectors included two Ritec μSPEC 1500 CZT (15 mm x 15 mm x 7.5 mm hemispherical crystals) detectors, and two φ38 mm x 38 mm LaBr detectors: one with standard Ce dopant and one Ce, Sr co-doped "enhanced" crystal with marginally better energy resolution. Enrichment algorithms included the General Enrichment Meter (GEM) program stewarded by the International Atomic Energy Agency (IAEA), the Square Wave Convolute (SWC) method developed at the Pacific Northwest National Laboratory (PNNL), and a generic region of interest method. Enrichment-assay precision was calculated for 1-, 5-, or 10-minute data acquisition times and compared against the IAEA International Target Values (ITVs) for different detector/algorithm pairs. This paper presents the field trial gamma-ray enrichment assay performance. Only the LaBr detectors analyzed with GEM and the SWC algorithm provided performance consistently superior to the ITVs. The LaBr detectors were significantly larger than the CZT, giving greater detection sensitivity and improved statistical precision, especially for lower enrichments and assay times. The LaBr detectors, specifically the co-doped variant, also had superior temperature stability compared to CZT, which improved their overall performance. [ABSTRACT FROM AUTHOR]

The International Atomic Energy Agency (IAEA) has developed an On-Line Enrichment Monitor (OLEM) as one possible component in a new generation of safeguards measures for uranium enrichment plants. The OLEM measures 235U emissions from the UF6 gas flowing through a unit header pipe using NaI(Tl) spectrometers, and corrects for gas density changes using pressure and temperature sensors in order to determine the enrichment of the gas as a function of time. In parallel with the OLEM instrument development, a Virtual OLEM (VOLEM) software tool has been developed that is capable of producing synthetic gamma-ray, pressure, and temperature data representative of a wide range of enrichment plant operating conditions. VOLEM complements instrument development activities and allows the study of OLEM for scenarios that will be difficult or impossible to evaluate empirically. Uses of VOLEM include: uncertainty budget analysis and performance prediction for typical and atypical operational scenarios; inter-comparison of candidate gamma-ray spectral analysis and enrichment estimation algorithms; and testing of the OLEM analysis and reporting software. This paper describes the technical foundations of VOLEM and illustrates how it can be used. An overview of the nominal instrument design and deployment scenario for OLEM is provided, with emphasis on the key online-assay measurement challenge: accurately determining the portion of the total 235U signal that comes from a background that includes solid uranium deposits on the piping walls. Monte Carlo modeling tools, data analysis algorithms and uncertainty quantification methods are described. VOLEM is then used to quantitatively explore the statistical uncertainty budgets and predicted instrument performance for a plausible range of typical plant operating parameters, and one set of candidate analysis algorithms. Additionally, a series of VOLEM case studies illustrates how an online enrichment monitor might respond in scenarios expected to be atypical, for example weak pressure transients or significant changes in background levels. [ABSTRACT FROM AUTHOR]