Year
2011
Abstract
Safeguards inspectors currently visit uranium enrichment plants to verify UF6 cylinder enrichment declarations. Measurements are performed with high-resolution, handheld detectors on a limited number of cylinders taken to be representative of the plant’s cylinder inventory. These enrichment assay methods interrogate only a small fraction of the total cylinder volume, and are time-consuming and expensive to execute. Pacific Northwest National Laboratory (PNNL) is developing a measurement methodology that could be incorporated into an automated UF6 cylinder verification station and that is based on the combined collection of traditional enrichment-meter data (186 keV photons from 235 U) and non-traditional, neutron-induced, highenergy gamma-ray signatures (3-8 MeV) with an array of collimated, medium-resolution scintillators. Previous work at PNNL demonstrated proof-of-principle that this hybrid method yields accurate, full-volume assay of the cylinder enrichment, reduces systematic errors when compared to several other enrichment assay methods, and provides simplified instrumentation and algorithms suitable for long-term, unattended operations. The objective of this system is to increase the number of inspected cylinders at higher accuracy and with lower cost compared to inspectors with hand-held instruments. In this document, several measurement campaigns of 30B cylinder populations and a refined MCNP model will be reported. The Monte Carlo N-Particle (MCNP) model consists of per-gram basis vectors for the different uranium isotopes and several fill geometries, enabling fast generation of any UF6 enrichment level and multiple configurations. The MCNP model was used to optimize collimator design and detector configuration for the hybrid method. In addition, a new field prototype based on model results was utilized in a set of field measurements and is reported here.