Plutonium flowsheet development in miniature mixer-settlers

Initial runs were completed in a new solvent extraction facility that has been built for testing coprocessing flowsheets with simulated LWR and FBR fuel solutions. The equipment, which is assembled in glove boxes, includes three 16-stage miniature mixer-settler banks with associated in-line monitors, pumping equipment, and sampling apparatus. Following shakedown runs with solutions containing uranium only, two flowsheet test runs were made with a simulated LWR fuel solution (U/Pu = 100). The solution was fed to an extraction-scrub bank, where 30% tributyl phosphate in normal paraffin hydrocarbon diluent was used to coextract uranium and plutonium. The extract was fed to a second mixer-settler bank, where all of the plutonium was stripped into an aqueous product stream using hydroxylamine nitrate for plutonium reduction; a controlled fraction of the uranium was simultaneously stripped to produce a U/Pu ratio of {similar_to}2. The amount of the uranium stripped with the plutonium was regulated by careful control of an organic backscrub stream. Finally, the residual uranium in the solvent was stripped in the third mixer-settler bank. The success of the experiments depended on precise control of very low liquid flow rates, and on in-line monitors which indicated the uranium or total heavy-metal concentrations. The most useful in-line device was the Mettler-Paar density meter, from which metal concentrations could be determined to within {similar_to}1 g/L. A miniature spectrophotometer also gave promising results for uranium analysis. Preliminary use of a Hewlett-Packard data acquisition system was satisfactory; recorded variables were temperature, solution density, liquid flow rates, and liquid levels