Development of methods for obtaining plutonium hexafluoride

Abstract

Methods for obtaining plutonium hexafluoride are examined: from high-to low-temperature using molecular and atomic fluorine and compounds -sources of atomic fluorine. It is shown that generation of atomic fluorine holds promise and plasma-chemical apparatus is desirable for obtaining plutonium hexafluoride. A schematic description is presented. The stages of model and natural tests of plasmachemical apparatus are described. A comparative assessment is given of different methods of obtaining plutonium hexafluoride.American researchers were the first to report, in the 1950s, that plutonium hexafluoride had been obtained and identified. Plutonium hexafluoride was synthesized by using molecular fluorine to fluoridate plutonium tetrafluoride at 900 K in a reactor with induction heating and by direct fluorination of plutonium compounds in a once-through reactor. Similar information about the initial stage of the development of the chemistry and technology of plutonium hexafluoride is presented in [1].The first experiments on obtaining plutonium hexafluoride at the Russian Science Center Kurchatov Institute were performed in 1957-1958. The reaction apparatus consisted of two parts: a bottom heated part and top part consisting of a dewar. Fluorination for supplying a constant excess during the reaction was accomplished in a fluorine stream. In the experiments, the rate of fluorination of plutonium tetrafluoride was measured, the activation energy of this reaction was determined, corrosion tests of various materials in a plutonium hexafluoride medium were performed, and its heat and radiation resistance were investigated.The high toxicity of plutonium compounds as well as certain particulars of handling them made it necessary to obtain plutonium hexafluoride in a closed volume. A laboratory thermosiphon -a closed system of two parallel tubes connected to one another -served for this purpose. One tube is heated and the other is cooled. Circulation occurs as a result of the density difference between the gases in the heated and cooled tubes. Under such conditions, the fluorine and plutonium hexafluoride formed are transferred from the reaction zone into the cooled tube, where the plutonium hexafluoride condenses and the fluorine returns to the reaction zone. For many years, the thermosiphon served for obtaining tens of grams of plutonium hexafluoride.To increase the productivity of the reactor for fluorinating plutonium compounds, the American researchers proposed using a fluidized bed. It is well known that the main advantage of a fluidized bed is high heat transfer and process monitoring, which makes it possible to stabilize the temperature in the reaction zone and obtain plutonium hexafluoride consistently. The fluorination of kilogram quantities of plutonium tetrafluoride in a reactor with a fluidized bed of corundum particles was studied in the Argonne National Laboratory [2]. The production of kilogram quantities of plutonium hexafluoride in a fluidized bed was demonstrated on a setup placed in a large glove box. To t...