AISI 304 L stainless steel decontamination by a corrosion process using cerium IV regenerated by ozone Part I: Study of the accelerated corrosion process

Abstract

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 l⁻¹ of cerium nitrate with bubbling of a 1.56 g h⁻¹ ozone flow in a 60 l 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.