Fluorine as a Safeguards Tool for Age-Dating of Uranium Oxyfluoride Particles?

Abstract

When uranium hexafluoride (UF6) is released into the environment, it reacts with the atmospheric moisture forming uranium oxyfluoride particles and HF. Fluorine-containing compounds such as HF are recognized as signatures for enrichment activities, but in this study the connection between the fluorine in the particles and the age of the particles has been investigated. Establishing this link is not evident, as uranium oxyfluoride particles are highly hygroscopic and little is known about their reaction mechanisms and stability. There are various environmental factors such as time, humidity and light or heat exposure that could affect the amount of fluorine, and even after the particles are collected the fluorine could decrease further due to sample preparation or storage conditions. The influence of (ultraviolet) light exposure combined with the time elapsed after preparation has been investigated on uranium oxyfluoride particles prepared at IRMM using the aerosol deposition chamber. The presence of fluorine in single particles was confirmed by SEM-EDX. Semi-quantitative information was obtained by evaluating specific SIMS peak height ratios. With these measurements, possible correlations existing between the amount of fluorine and the age of a particle could be investigated, taking into account the environmental conditions to which the uranium oxyfluoride particles were exposed.