Characterization of an Enriched Uranyl Fluoride Deposit in a Valve and Pipe Intersection Using Time-of-Flight Transmission Measurements with 252Cf

A method was developed and successfully applied to characterize large uranyl fluoride (UO2F2) deposits at the former the Oak Ridge Gaseous Diffusion Plant. These deposits were formed by a wet air in-leakage into the UF6 process gas lines over a period of years. The resulting UO2F2 is hygroscopic, readily absorbing moisture from the air to form hydrates as UO2F2 - nH2O. The ratio of hydrogen to uranium can vary from 0 - 16, and has significant nuclear criticality safety impacts for large deposits. In order to properly formulate the required course of action, a non-intrusive characterization of the distribution of the fissile material within the pipe, its total mass, and amount of hydration was necessary. The Nuclear Weapons Identification System1 (NWIS) previously developed at the Oak Ridge Y-12 Plant for identification of uranium weapons components in storage containers was used to successfully characterize these deposits.