Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Taniguchi, Naoki; Kawakami, Susumu; *
JNC TN8400 2001-025, 27 Pages, 2002/03
JNC-TN8400-2001-025.pdf:1.16MB
It is essential to understand the corrosion type of carbon steel under the repository conditions for the lifetime assessment of carbon steel overpack used for geological isolation of high-level radioactive waste. According to the previous study, carbon steel is hard to passivate in buffer material assuming a chemical condition range of groundwater in Japan. However, concrete support will be constructed around the overpack in the case of repository in the soft rock system and groundwater having a higher pH may infiltrate to buffer material. There is a possibility that the corrosion type of carbon steel will be influenced by the rise of the pH in groundwater. In this study, anodic polarization experiments were performed to understand the passivation condition of carbon steel in buffer material saturated with water contacted with concrete. An ordinary concrete and a low-alkalinity concrete were used in the experiment. The results of the experiments showed that the carbon steel can passivate under the condition that water having pH 
13 infiltrate to the buffer material assuming present property of buffer material. If the low-alkalinity concrete is selected as the support material, passivation can not occur on carbon steel overpack. The effect of the factors of buffer material such as dry density and mixing ratio of sand on the passivation of carbon steel was also studied. The results of the study showed that the present property of buffer material is enough to prevent passivation of carbon steel.
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.
Yamazaki, Kazutoshi*; Takao, Hajime*; Kikuchi, Takahiro*; Kuriki, Yoshiro*; Kobayashi, Masato*; Kawakubo, Masahiro*; Shirase, Mitsuyasu*; Iwata, Yumiko*; Tochigi, Yoshikatsu*; Nakayama, Gen*; et al.
no journal, ,
Among factors affecting the corrosion behavior of carbon steel overpack, in order to consider materials (size) and realistic environmental factors which are difficult to reproduce in the laboratory scale test, engineering scale tests in the underground environment were carried out. A mock-up test of the same scale was also carried out on the ground with the aim of controlling and evaluating factors that govern the corrosion phenomenon. As a result of the test for about 3 years, there was no big difference between the average corrosion amount and the maximum corrosion amount of the simulated overpack base metal and the welded part. On the other hand, unlike the laboratory scale test, localization of corrosion due to the adhesion between the buffer material and the simulated overpack was also confirmed during the initial transient period.