Development of chemical decontamination process with sulfuric acid-cerium (IV) for decommissioning. System decontamination process with electrolytic regeneration of Ce4+ from Ce3+.

The electrolytic regeneration of Ce4+ from Ce3+, which is required to achieve a high decontamination factor (DF) in this process, has been investigated. A calculating model was derived for the regenerating current required during the decontamination as a function of dissolution rate of crud, corrosion rate (Rc ), current efficiency (ηe ) and characteristics of decontamination loop. From the above calculation, it was found that the current was mainly governed by Rc and ηe . A condition to obtain a high DF at low Rc and high ηe has been found experimentally by use of a mixture of Ce3+ and Ce4+ at the ratio of Ce4+/Ce3+=0.1∼0.2. The desired values to be ηe ≧80% at above 50 A/m2 was obtained under the flow rate above 300 cm/min and Ce3+ concentration above 10x10−3M at 60°C using the dual-cylindrical type cell. The current efficiency was also investigated with cells of various geometries. The present decontamination process has been proposed as a system decontamination process, which is essentially a single-step decontamination process for Cr-rich oxides.