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

Abstract

The dissolution of Cr-rich oxides in and the decontamination of contaminated specimens by sulfuric acid-Ce(IV) (SC) solution have been investigated. The results have been com-pared with those by the reported typical decontamination reagents. The SC solution can dissolve simultaneously not only Cr but also Fe and Ni in the Cr-rich oxides. The dissolution mainly depends on Ce(IV) concentration (1.3–10−3 M) and temperature (40–90°C), but is independent of H2SO4-concentration (0.2–0.5 M at 5 x 10−3M Ce(IV)). The DF is ca. 33 at 90°C for 24 h with 0.25 M H2SO4-5 x 10−3M Ce(IV). Under electrolytic regeneration of Ce(IV) from Ce(III) during the decontamination, the DF is raised to 460 even at 80°C for 24 h with 0.25 M H2SO4-1.3 x 10−3M Ce(IV). The SC solution can be applicable to the decontamination for decommissioning of both BWR and PWR. Fcrthermore the combination of the chemical cleaning with an additional ultrasonic cleaning provides a promissing cleaning procedure for post-disassembly components.