SIMULATION STUDY ON BEHAVIOR OF TECHNETIUM AND ITS CONTROLLED STRIP DURING CODECONTAMINATION PROCESS OF FUEL-REPROCESSING

Behavior of Tc(VII) in the codecontamination process of the Purex was analyzed using various flowsheet conditions with the EXTRA.M code, whi ch includes a numerical model of distsibution ratio of Tc(VII). The en hancing effect of Zr(IV) on the extraction of Tc(VII) was investigated as functions of the concentration of Zr(IV) in the feed solution, i.e . 0.05 approximately 1.0 g.l-1, and the flow rate of the Tc(VII) strip ping solution. A sufficient flow rate of a high-acid strip, i.e. 5 mol .l-1 HNO3 is necessary depending on the Zr(IV) concentration to achiev e a complete stripping of Tc into an aqueous waste stream. Under a rel atively high concentration of Zr(IV) and the high-acid strip, the conc entration profile of Tc(VII) showed an accumulation in the process. To avoid, if necessary, the accumulation of Tc(VII) and a high aqueous f low rate at the scrub part. a by-pass flowsheet, in which the Tc-strip ped solution is passed over the scrub part and connected to the extrac tion stage, was proposed. In the actual reprocessing of spent fuel, de termination of the flow rate of high-acid strip and subsequent decisio n regarding the by-pass mode or non-by-pass mode should be done depend ing on the amount of Zr(IV) in the fuel to be processed.