Development of chemical decontamination process with sulfuric acid-cerium (IV) for decommissioning

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+ 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 10 x 10-3 M at 60 deg 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. (author)