Hybrid Enrichment Verification Array: Module Characterization Studies

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

“…Unfortunately, composition of wall deposits and heel material is not well understood. They are commonly thought to be made of non-uranium, progeny compounds, UF4, or some mix of remaining UF6 (McDonald et al 2011;Zalavadia et al 2016). Operationally, heels cylinders are sometimes given time to decay for several weeks before they meet the dose limits for transport, indicating that there are not many uranium atoms left to keep producing radioactive progeny, and that the majority of the wall deposits are made of non-uranium compounds.…”

“…An investigation of energy calibration approaches indicated that a linear function is most appropriate for determination of the lower bound of the HEVANT region of interest (3.0 MeV), when using a three-point calibration based on the 186-keV, 765-keV, and 1001-keV lines expected to be available in each cylinder occupancy spectrum. This three-point linear calibration was used for the HEVANT analysis presented in this report (Zalavadia et al 2016).…”

“…PNNL performed modeling and measurements to support a revision of the HEVA module design and data acquisition methods. This work is described in detail by Zalavadia et al (2016); highlights are presented here.…”

“…This material is often labeled "heels" and/or "wall deposits" (hereafter, wall deposits for simplicity) and generally speaking, its volume and mass grow with the number of fillings that a given cylinder has experienced. Worst-case assumptions (in terms of expected count rates) about the geometry, elemental composition, and isotopic inventory were adopted in the modeling study, as described by Zalavadia et al (2016).…”

“…Laboratory measurement of the intrinsic neutron efficiency for the HEVA nontraditional method produced a value of approximately 0.5%, assuming a gamma-ray region of interest from 3.0 to 8.0 MeV. It was shown that the contribution of the steel layers is relatively small compared to the prompt gamma rays produced in the detector crystal (Zalavadia et al 2016).…”