Hybrid Enrichment Assay Methods for a UF6 Cylinder Verification Station: FY10 Progress Report

Abstract

SummaryPacific Northwest National Laboratory (PNNL) is developing the concept of an automated UF 6 cylinder verification station that would be located at key measurement points to positively identify each cylinder, measure its mass and enrichment, store the collected data in a secure database, and maintain continuity of knowledge on measured cylinders until the arrival of International Atomic Energy Agency (IAEA) inspectors. At the center of this unattended system is a hybrid enrichment assay technique that combines the traditional enrichment-meter method (based on the 186-keV peak from 235 U) with nontraditional neutron-induced high-energy gamma-ray signatures (spawned primarily by 234 U alpha emissions and 19 F(α,n) reactions). Previous work by PNNL provided proof-of-principle for the nontraditional signatures to support accurate, full-volume interrogation of the cylinder enrichment, thereby reducing the systematic uncertainties in enrichment assay due to UF 6 heterogeneity and providing greater sensitivity to material substitution scenarios [Smith 2009;Smith In press].The work described here builds on that preliminary evaluation of the non-traditional signatures, but focuses on a prototype field system utilizing NaI(Tl) and LaBr 3 (Ce) spectrometers, and enrichment analysis algorithms that integrate the traditional and non-traditional signatures. Results for the assay of Type-30B cylinders ranging from 0.2 to 4.95 wt% 235 U, at an AREVA fuel fabrication plant in Richland, WA, are described for the following enrichment analysis methods: 1) traditional enrichment meter signature (186-keV peak) as calculated using a square-wave convolute (SWC) algorithm; 2) nontraditional high-energy gamma-ray signature that provides neutron detection without neutron detectors and 3) hybrid algorithm that merges the traditional and non-traditional signatures. Uncertainties for each method, relative to the declared enrichment for each cylinder, are calculated and compared to the uncertainties from an attended HPGe verification station at AREVA, and the IAEA's uncertainty target values for feed, tail and product cylinders. Table 1 provides a summary of those results below. Traditional NaI (SWC method) 3.5 7.9 13Non-Traditional NaI 3.7 4.9 32Hybrid NaI (simple average) 2.5 4.6 9.71 The target uncertainties are estimated from the combination of systematic and random errors given in Kuhn and should be used only to set the scale of the target uncertainties.iv A summary of the major findings from the field measurements and subsequent analysis follows:• Traditional enrichment-meter assay using specially collimated NaI spectrometers and a SquareWave-Convolute algorithm can achieve uncertainties comparable to HPGe and LaBr for product, natural and depleted cylinders.• Non-traditional signatures measured using NaI spectrometers enable interrogation of the entire cylinder volume and accurate measurement of absolute 235 U mass in product, natural and depleted cylinders.• A hybrid enrichment assay method can achieve lower uncertainties than e...

Viability Study for an Unattended UF₆ Cylinder Verification Station: Phase I Final Report

“…A graphical comparison of the HEVAhybrid and HEVAT E235 values are shown in Figure 53 for the URENCO All population. It is evident there is the reduction in uncertainties when hybridizing two HEVA signatures that have a low degree of statistical correlation of errors, as asserted by prior work (Smith et al 2010a). To confirm this prior finding, a statistical analysis of the HEVAT and HEVANT signatures for the URENCO All population was performed.…”

“…Previous statistical analysis by PNNL, using cylinders measured in prior field trials, demonstrated that the uncertainties for the nontraditional (neutron) and traditional (186-keV) signatures show a low degree of correlation, indicating that combining the two signatures will produce more precise verification results than either signature acting independently (Smith et al 2010a). In this study, this hybrid analysis is performed with a simple averaging (i.e., even weighting) of the traditional and nontraditional signatures.…”

“…Previous experience in applying the square-wave filter has indicated that it eliminates linearly varying background quite effectively but exhibits sensitivity to nonlinearities in the continuum shape above the 186-keV region (Smith et al 2010a;Smith et al 2010b;McDonald et al 2011;Jordan et al 2012). When the intensity of this continuum varies substantially over a cylinder population (e.g., as in Figure 12) or even within a cylinder, the convolute peak amplitude in the 186-keV region reflects not only the intrinsic variation in the 186-keV peak area, but also the impact of the residual continuum shape that is not eliminated completely by the filter.…”

“…The traditional 186-keV signature provides a direct measure of E235. Under assumptions of known 234 U/ 235 U behavior in the plant, the nontraditional total neutron signal can be calibrated to total M235 in the cylinder (Smith et al 2010a;Smith et al 2010b;McDonald et al 2011;Smith 2015). Figure 8.…”

Automated UF6 Cylinder Enrichment Assay: Status of the Hybrid Enrichment Verification Array (HEVA) Project: POTAS Phase II

“…PNNL research conducted in the 2009 to 2012 timeframe has provided proof-of-principle for the non-traditional signatures to support accurate, full-volume interrogation of the cylinder enrichment, thereby reducing the systematic uncertainties in enrichment assay due to UF 6 heterogeneity and providing greater sensitivity to material substitution scenarios [Mace 2010, Smith 2009, 2010a. We have also investigated spectrum analysis techniques supporting robust, automated implementation of the traditional enrichment-meter signature.…”