AISI 304 L stainless steel decontamination by a corrosion process using cerium IV regenerated by ozone

This paper describes the study of a new decontamination process of AISI 304L stainless steel from dismantled nuclear power plants. A very thin active contaminated surface layer was stripped from the underlying metal by corrosion in a solution of nitric acid with the addition of cerium nitrate. The Ce4+/Ce3+ concentration ratio was initially equal to unity and ozone/oxygen bubbles were used to regenerate Ce3+ ions into Ce4+ ions. The study was performed in a laboratory cell prior to preliminary optimization in a three-litre reactor. The objective was to obtain a corrosion rate of about 10 micrometers per day. This target was reached in 10-2 mol 1-1 of cerium nitrate with bubbling of a 1.56 g h-1 ozone flow in a 60 1 h-1 total gas flow. The corrosion rate depended essentially on the Ce4+ concentration. The stainless steel exhibited intergranular corrosion. The corrosion rate was monitored by measuring the solution oxidizing potential using a precious metal electrode.