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Industrial & Engineering Chemistry Research, Vol.45, No.13, 4461-4470, 2006
Studies on the process development for the chemical decontamination of stainless-steel systems: Novel observations
A two-step oxidative-reductive dilute chemical decontamination process for boiling water reactors (BWRs) is evaluated for obtaining quantitative dissolution of corrosion product oxides, minimum waste, and efficient removal of ionic load. Oxidative dissolution of Cr2O3 using a solution of nitric acid and potassium permanganate or permanganic acid was equally efficient. The dissolution of chromia continued in both of these oxidizing media, even under permanganate-deficient conditions. Ascorbic acid was a more effective reducing agent than hydrazine for the reductive dissolution of hematite and the hematite + magnetite mixture. Ion-exchange treatment of the spent dissolution formulation to accomplish a multicycle mode of dissolution, without intermediate draining, indicated the generation of nonionic organic compounds in solution when ascorbic acid acted as a more-than-two-electron reductor. However, using oxalic acid for the reduction of residual permanganate/MnO2 and ascorbic acid for chromate/lattice iron reduction alleviated this problem. Ion exchangers were evaluated for radiation stability and for performance in mixed-bed and stratified-bed configurations. The stratified bed was advantageous, in terms of total ionic load removal for a given amount of resin.