From abstract: "The circumstances are described pertaining to an explosion in a TNX evaporator during the concentration of a uranyl nitrate-nitric acid solution. TBP and Amsco diluent were probably present in the evaporator charge. A laboratory program involving small-scale atmospheric and closed-vessel distillations of various mixtures of UNH, HNO3, Amsco, TBP, and water indicate that an exothermic reaction between TBP and UNH, or between TBP and HNO3, or both, was responsible for the explosion. The danger areas of temperature, TBP concentration, pressure, and heating rate are defined and recommendations are made for safe evaporator operation.