Development of chemical decontamination process with sulfuric acid-cerium (IV) for decommissioning. Demonstration test at JPDR recirculation system.

The new decontamination process using sulfuric acid-cerium (IV) solution (SC process) for reactor dismantling has been developed and demonstrated to evaluate its applicability at the recirculation system of the JPDR (A-loop). The decontamination test loop with the surface area of 42.7 m2 (contaminated area of 9.2 m2) and solution volume of ca. 2.3 m3 consisted of the main circulation, Ce4+-regeneration and waste solution treatment lines. The decontaminationstep was operated with continuous electrolytic regeneration of Ce4+ from Ce3+ to maintain the Ce4+ concentration in the range of 12×10-3 M at Ce4+/Ce3+≤0.1.The test results are summarized as followed: (1) The decontamination factors (DF) for sampling specimens after the decontamination were ranged 3601, 800. (2) The corrosion rate of the test loop increased linearly with a flow rate (0.552.6 m/s) in the presence of Ce4+. (3) Burst of scale (similar to cruds) in the early stage of the decontamination led to the decrease of Ce4+ concentration. (4) The desired values to be a current efficiency ηe≥80% at 50A/m2 was obtained in the electrolytic regenerating cell.The results of demonstration test on the SC process indicate that a high decontamination factor can be obtained in a low Ce4+ concentration by means of its electrolytic regeneration.