Low Corrosive Chemical Decontamination Method Using pH Control, (I) Basic System

Abstract

A new low corrosive decontamination method was developed which uses both oxalic acid and hydrazine as the reducing agent and potassium permanganate as the oxidizing agent. Less corrosion of structural materials during the decontamination is realized by pH control of the reducing agent. The pH of 2.5, attained by adding hydrazine to oxalic acid, was the optimum pH for maintaining a high decontamination effect and lowering the corrosion at the same time. As this reducing agent can be decomposed into carbon dioxide, nitrogen and water by using a catalyst column with hydrogen peroxide, the amount of secondary radioactive waste is small. These good features were demonstrated through actual plant decontamination tasks.

Effect of Oxidizing Decontamination Process on Corrosion Property of 304L Stainless Steel

“…Chemical decontamination is an effective method to reduce occupational radiation exposure during large-scale maintenance tasks such as the overhaul of primary recirculation pumps and shroud replacement in in-service nuclear power plants (NPPs) [7]. Therefore, many different chemical decontamination methods have been developed [8][9][10][11][12][13][14][15], such as HP/CORD (Chemical Oxidation Reduction Decontamination), AP/CITROX (Citric plus Oxalic acids), and LOMI (Low Oxidation state Metal Ion). Each has its own merits and demerits.…”

“…Especially in Pressurized Water Reactor (PWR) conditions, the decontamination process calls for oxidation of these Cr ions from trivalent to hexavalent, which form more easily soluble species. Among the various known pretreatment chemicals, the permanganate-based reagents are known to be the most efficient [13][14][15]. Resulting from a decontamination procedure performed, the corrosion rate of the metals may eventually be increased; therefore, to minimize the corrosion damage, the preparation of perfectly clean and passive surfaces in addition to a chemical decontamination is strongly recommended.…”

Water chemistry technology – one of the key technologies for safe and reliable nuclear power plant operation

“…CORD by Siemens, HOP by Hitachi and T-OZON by Toshiba, have been developed [60][61][62]. One of the difficulties of decontaminations is even if a sufficient DF is obtained during the decontamination processes, dose rate might easily return its previous level or sometime even more than the previous level (Figure 13(a)).…”

Development of a Suppression Method for Deposition of Radioactive Cobalt after Chemical Decontamination: (I) Effect of the Ferrite Film Coating on Suppression of Cobalt Deposition

“…Hydrogen peroxide and hydrazine can be decomposed into water and gas components by the catalyst used for the hydrazine, oxalic acid and potassium permanganate (HOP) chemical decontamination process. 7) Ferrous ions are produced by dissolving iron in organic acid solution with nitrogen bubbling to remove oxygen. Organic acid can also be decomposed into water and carbon dioxide by the catalyst of the HOP process.…”