PROGRESS IN REAL-TIME MONITORING FOR CONTROLLING THE COMPOSITION OF THE URANIUMPLUTONIUM NITRATE PRODUCT IN A TRI-BUTYL PHOSPHATE BASED FLOWSHEET

摘要

Nuclear fuel recycling flowsheets that do not fullyseparate plutonium (Pu) from uranium (U) are of interestdue to reduction in the Pu attractiveness level, and thepotential to simplify the manufacturing of mixed oxidefuel. Our research in this regard has not been directed atdevelopment or testing of a particular flowsheet forindustrial application, but rather at examining how well aparticular U/Pu mass ratio (chosen to be 7/3 for thisproject) can be maintained using laboratory-scalecounter-current solvent extraction equipment (2-cmcentrifugal contactors). Integral to this effort is thedeployment of real-time optical spectroscopic tools tomonitor the U/Pu ratio in the product stream, so thatadjustments to process parameters can be made toachieve and maintain the targeted U/Pu ratio.In the co-decontamination (CoDCon) flowsheettested in this work, the co-extraction of U and Pu followsstandard protocol for a tri-butyl phosphate (TBP) basedflowsheet. The Pu is stripped from the solvent usingU(Ⅳ). The control point for adjusting the U/Pu ratio isthe flowrate of a TBP solvent stream used to extract U(Ⅳ)from the aqueous phase in the Pu stripping contactorbank. In a conventional recycling operation, the flowrateof this TBP solvent stream would be sufficiently high toquantitatively extract the U(Ⅳ) so that a pure Pu productis obtained. However, as the flowrate of this stream isdecreased, the amount of U(Ⅳ) remaining in the aqueousphase (i.e., with the Pu) increases. The novel aspect ofour approach is the real-time monitoring of the U/Puratio in the U/Pu product stream using opticalspectroscopy coupled with chemometric modeling. Thisreal-time feedback allows adjustment of the TBP solventflowrate to achieve the target U/Pu ratio.Several runs of the flowsheet have been conductedusing simulated dissolved fuel solutions. Monitoring andcontrol of the U/Pu ratio has been demonstrated in allcases. Once steady-state is reached, very stable control ofthe U/Pu ratio can be achieved. Our observations are thatthe uncertainties in the final U/Pu product are dominatedby the uncertainties in the analytical methods used toanalyze the product obtained, rather than in operation ofthe solvent extraction equipment.