Re-oxidation behavior of Cr and V ions in the boiling nitric acid solution and acceleration effect on corrosion rate of stainless steel

摘要

Nuclear fuel reprocessing is an important process for efficient usage of uranium resources. A large amount of nitric acid solution is used in Purex process which is adopted in Japanese nuclear fuel reprocessing plant (1). The materials of this plant are exposed in severe corrosive environment. Therefore, many types of equipment are made of corrosion resistant materials, i.e. austenitic stainless steel, titanium alloy and zirconium. Some reports pointed out that stainless steel was corroded at trans-passive state caused by several anodizing ions included in nitric acid solution (2-6). They introduced the characteristics of corrosion and improved materials in this environment. For example, Kajimura showed improved material reduced C, P and S content from austenitic stainless steel (6). And also, Cr, Ce, Ru Pu and Np were reported for the chemical species accelerated corrosion (3,5,7-9).rnAmong these chemicals, Pu and Np are radioactive and included in spent nuclear fuels. We have already reported that small amount of Np addition in the nitric acid solution accelerated corrosion rate dominantly (7). We suggested that Np was probably re-oxidized in the boiling nitric acid solution but the actual evidence was not obtained because of difficulties of handling Np. The solution containing Np must be handled in the specially designed laboratory so-called "hot Lab".rnBy the way, Cr and V were used substituting for these radioactive ion included in spent nuclear fuel (8-10). It was because that corrosion feature was similar as intergranular corrosion and the degree of accelerating corrosion rate was almost similar. It is expected that accurate analyses of the effect of these ions lead to understanding the mechanism of corrosion acceleration of Np ion addition.rnIn this report, we examined re-oxidation behavior in the boiling nitric acid solution and acceleration effect on corrosion rate of stainless steel using Cr and V ions