THE PUREX THERMODYNAMICS OF PLUTONIUM(IV) AND URANIUM(VI) MACROCONCENTRATIONS COEXTRACTION INTO TRI-N BUTYLPHOSPHATE - NEW DATA AND NEW MODELS

The modern worldwide Purer technology (spent nuclear fuel reprocessing ) is based on solvent extraction of actinides (U, Pu) in a system with aqueous nitric acid solutions and organic (n-paraffins) solutions of tri-n-butylphosphate (TBP). To the creation of a universal mathematica l process model contributes - first of ail - the knowledge of uranium( VI), plutonium(IV) and nitric acid equilibrated distribution data. Fur ther should be included the field of all the technological (''know-how '') operations, in particular, so-called strong-and-weak-acid and high -and-ambient-temperature scrubs of the actinide bearing organic phase. To enrich the Purer data base with additional information the new ori ginal values of equilibrium distribution coefficients of Pu(IV) (0.06- 28 g/l), U(VI) (0.18-150 g/l) and nitric acid (0.01-10.5 mol/l) (in al l the cases - equilibrated aqueous phase concentrations) - at reliable organic solution homogeneity (i.e. without ''third'' phase formation phenomena) were obtained. Those results include data at 25 and 60 degr ees C, of 20 and 30 vol% TBP (in n-dodecane). All the analyses of the metal content were performed using original gamma-spectrometric proced ure of simultaneous U and Pu determination. Using both obtained data a nd known results (no less than 700 ''systems'' type of ''U(VI)-Pu(IV)- water-nitric acid-TBP-n-dodecane'') the simple regressive equations (t wo third-power polynominal series) were developed, which with an accur acy better than +/-8% permit to calculate the distribution of the thre e mentioned components. The developed equations of the concentration d ependence of the distribution coefficients (D) for all the components have the general form: GRAPHICS where i + k + m less than or equal t o 3; n = Pu, U, HNO3. The high-performance models are recommended for development of operating programs - as a modifier of today's Purer per formance.