The Purex thermodynamics of plutonium(IV) and uranium(VI) macroconcentrations coextraction into tri-n butylphosphate: new data and new models

The modern worldwide Purex 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 mathematical process model contributes - first of all - the knowledge of uranium(VI), plutonium(IV) and nitric acid equilibrated distribution data. Further 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 Purex data base with additional information the new original 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 all 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 C, of 20 and 30 vol% TBP (in n-dodecane). All the analyses of the metal content were performed using original gamma-spectrometric procedure of simultaneous U and Pu determination. Using both obtained data and known results (no less than 700 ''systems'' type of ''U(VI)-Pu(IV)-water-nitric acid-TBP-n-dodecane'') the simple regressive equations (two third-power polynominal series) were developed, which with an accuracy better than ±8% permit to calculate the distribution of the three mentioned components. The developed equations of the concentration dependence of the distribution coefficients (D) for all the components have the general form: where i+k+m≤3; n=Pu, U, HNO3. The high-performance models are recommended for development of operating programs - as a modifier of today's Purex performance. ((orig.))