Zirconium Thorex process

More recently a flowsheet has been developed which employs 30% TBP/OK as the solvent.349-446 447 This involves the use of an acid feed to the first cycle to assist in zirconium decontamination and suppress hydrolysis. An acid-deficient partition cycle then follows in which the U-Th separation is effected. A pilot plant (JUPITER) has been constructed at Julich in Germany to process Th02/U02 fuel using this flowsheet. Although a complete separation of thorium, uranium and FPs is possible using TBP in the Thorex process,448 alternative approaches... 

It is also of interest to note that the effect of DBP on zirconium separation from thorium in the Acid-Thorex system is different than zirconium separation from uranium in the Purex system.(Figure k) The Purex data are from reference 6 and the Acid-Thorex data are from General Atomic Company pilot plant studies. The thorium probably forms a stronger DBP complex than does uranyl ion and, therefore, the amount of uncomplexed DBP available for raising the equilibrium distribution of zirconium would be less in the Acid-Thorex process. 

Figure 10.26 compares the low-concentration distribution coefficients of uranium, thorium, plutonium, protactinium, and the principal fission products. The spread between thorium and fission-product zirconium is greatest between 1 and 2 M HNO3, the range used in the decontamination step of the acid Thorex process. Because the distribution coefficient of protactinium is close to that of thorium, it is necessary to remove protactinium or complex it with fluoride or phosphate ion to prevent its extraction with thorium. 

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