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JAEA Reports

Long-term immersion tests of engineered materials in the Tono mine; Results for metals

Hama, Katsuhiro; Taniguchi, Naoki; Honda, Akira

JNC TN7430 2000-002, 25 Pages, 2001/01

JNC-TN7430-2000-002.pdf:3.32MB

The burial tests of mild steel and pure titanium were performed in a gallery at Tono mine to assess the corrosion resistance of these materials under goundwater environment. Specimens were placed in the container and immersed into groundwater. After the immersion period, the apperance of the surface of these specimens were observed. The corrosion product of mild steel specimen was analysed by various methods. The average corrosion rate of mild steel for 10 years was assessed by the measurement of the weight loss of carbon steel specimen. The results of the test were summerised as follows : (1)The average corrosion rate of mild steel for 10 years was assessed to be 4.36 10 $^{-3}$ mm/y by the weight loss of the specimen. (2)The corrosion product consists of outer porous substance and inner tight corrosion product film. The former contains ferric oxide such as goethite and the latter contains ferrous oxide such as magnetite. (3)The evidence of the initiation of localised corrosion was not observed on the titanium specimens.

JAEA Reports

Effect of magnetite as a corrosion product on the corrosion of carbon steel overpack

Taniguchi, Naoki; ; Kawasaki, Manabu*; Masugata, Tsuyoshi*

JNC TN8400 2001-001, 56 Pages, 2000/12

JNC-TN8400-2001-001.pdf:2.05MB

It is necessary to clear the effects of corrosion products on the corrosion life time of carbon steel overpack for geological isolation of high-level radioactive waste(HLW). Especially, it is important to understand the effects of magnetite because magnetite as a simulated corrosion product is reported to accelerate the corrosion rate of carbon steel. In this study, corrosion tests to reproduce the acceleration of corrosion due to magnetite was performed and the mechanism of the acceleration was investigated to evaluate the effects of magnetite as a corrosion product. Based on the results of experiments, following conclusions are obtained ; (1)Magnetite powder accelerates the corrosion rate of carbon steel. The main reaction of corrosion under the presence of magnetite is the reduction of Fe(III) in magnetite to Fe(II), but the reaction of hydrogen generation is also accelerated. The contribution of hydrogen generation reaction was estimated to be about 30% in the total corrosion reaction based on the experimental result of immersion test under the presence of magnetite. (2)Actual corrosion products containing magnetite generated by the corrosion of carbon steel protect the metal from the propagation of corrosion. The corrosion depth of carbon steel overpack due to magnetite was estimated to be about 1 mm based on the results of experiments. Even if the effect of magnetite is taken into the assessment of corrosion lifetime of overpack, total corrosion depth in 1000 years is estimated to be 33 mm, which is smaller than the corrosion allowance of 40 mm described in the second progress report on research and development for the geological disposal of HLM/ in Japan. It was concluded that the effect of magnetite on the corrosion life time of carbon steel overpack is negligible.

JAEA Reports

Study on cathodic reaction control efficiency by low alloy steels

Akashi, Masatsune*; Fukaya, Yuichi*; Asano, Hidekazu*

JNC TJ8400 2000-015, 46 Pages, 2000/02

JNC-TJ8400-2000-015.pdf:2.96MB

Difference of hydrogen generation phenomena on the surface of the Steels were not observed between carbon steel, atmospheric corrosion resisting steel and 5%-Ni steel. Rust layer was formed on these three-type of steels by steam oxidation method. And the chemical composition of the rust for the steels were basically two (2) layers structure for the previous two steels as hematite (Fe $_{2}$ O $_{3}$ ) based for the outer layer and magnetite (Fe $_{3}$ O $_{4}$ ) based for the inner layer. And for the last steel, it had three (3) layer in the rust as hematite (Fe $_{2}$ O $_{3}$ ) based for the outer layer, magnetite (Fe $_{3}$ O $_{4}$ ) based for the intermediate layer and Ni based layer for the inner layer. These steels showed mostly same Tafel gradient in their cathodic polarization curves compare with that for no rust specimens. However, the exchange current density which reaction is assumed as a hydrogen generation reaction was largely increased. The cathodic reaction for each steels whose surface is covered by magnetite layer might be accelerated, then the corrosion rate was considered as accelerated, too.

JAEA Reports

Study on cathodic reaction control efficiency by low alloy steels

Akashi, Masatsune*; Fukaya, Yuichi*; Asano, Hidekazu*

JNC TJ8400 2000-014, 22 Pages, 2000/02

JNC-TJ8400-2000-014.pdf:0.75MB

Difference of hydrogen generation phenomena on the surface of the Steels were not observed between carbon steel, atmospheric corrosion resisting steel and 5%-Ni steel. Rust layer was formed on these three-type of steels by steam oxidation method. And the chemical composition of the rust for the steels were basically two(2) layers structure for the previous two steels as hematite(Fe $_{2}$ O $_{3}$ ) based for the outer layer and magnetite(Fe $_{3}$ O $_{4}$ ) based for the inner layer. And for the last steel, it had three(3) layer in the rust as hematite(Fe $_{2}$ O $_{3}$ ) based for the outer layer, magnetite(Fe $_{3}$ O $_{4}$ ) based for the intermediate layer and Ni based layer for the inner layer. These steels showed mostly same Tafel gradient in their cathodic polarization curves compare with that for no rust specimens. However, the exchange current density which reaction is assumed as a hydrogen generation reaction was largely increased. The cathodic reaction for each steels whose surface is covered by magnetite layer might be accelerated, then the corrosion rate was considered as accelerated, too.

JAEA Reports