Non-destructive Examination of Multiphase Material Distribution in Uranium Hexafluoride Cylinders Using Steady-State Laser Doppler Vibrometery

Abstract

The ability to detect the diversion of a significant quantity of nuclear material is the objective of international nuclear safeguards, and safeguarding uranium enrichment technology is especially important in preventing the spread of nuclear weapons. In gas centrifuge enrichment plants, the uranium is in the form of uranium hexafluoride (UF₆), which regularly transitions between phases during processing and storage due to its low triple point. The variation of material distribution in Uf₆ cylinders has a significant effect on enrichment measurement uncertainty, especially with increasing accuracy of passive neutron assay measurements, motivating interest in non-destructive methods of examining UF₆ cylinder fill distributions.

For this study, a novel steady-state scanning laser Doppler vibrometer (LDV) system is used to determine the material and phase distributions within small UF₆ cylinders. This technology induces steady-state ultrasonic waves throughout an object and then uses a scanning laser to measure vibrational wavenumber at pixilated points on the object. Different materials and phases are excited by the ultrasonic waves to different extents, changing the local measured wavenumbers and allowing fill distributions of the storage cylinders to be mapped. Through non-destructive examination of the variation in typical fill profiles of UF₆ cylinders, the uncertainty associated with neutron measurements of UF₆ cylinders may be better characterized.