Fractionation of UF6 and daughter progeny in storage cylinders from external heating

Uranium hexafluoride (UF6) is a significant concern for material accountancy and verification in the international safeguards community. Verification of the contents of UF6 cylinders is generally attempted with gamma spectroscopy but the current methods assume a uniform, homogeneous UF6 mass distribution within the cylinder. In this work, it was found experimentally and confirmed via modeling, that under an external heat load (the sun), the UF6 and its daughter products undergo fractionation in the cylinder. This fractionation of the UF6 and daughter products can cause an errant measurement of the enrichment of the cylinder when using the current verification methods.