Design and test of a thermosiphon evaporator for acid-deficient uranyl nitrate

The reference process to recycle 233U to HTGRs begins with the receipt of the 233UO2(NO3)2 product solution from a reprocessing plant, which is fed to a resin loading system. The nitrate is removed by extraction with a liquid organic amine. By adding an evaporator to remove water, a continuous, high-efficiency process for loading uranium on ion exchange resin is possible. A vertical thermosiphon evaporator was designed, fabricated, and tested with natural uranium to meet the requirements of the HTGR fuel recycle Hot Engineering Test Facility. The thermosiphon evaporator, which was designed to produce 60 liters of condensate per hour containing less than 1 ppM of uranium, performed satisfactorily and was simple to control. The uranyl nitrate solution was circulated continuously through the evaporator during operation of the resin loading system, with the liquid level being determined by a fixed overflow jackleg. The evaporation rate was controlled by regulating the steam supply pressure. The condensate contained less than 0.5 ppM of uranium, and the uranium decontamination factors (DFs) were 5 x 105 to 1 x 106 at boilup rates of 17 to 79 liters/hr. This evaporator design is adequate for remote operation, control of criticality, and other requirements for the proposed application