Corrosion monitoring in humidity-controlled environment simulating gamma ray irradiation

Omori, Atsushi*; Akiyama, Eiji*; Abe, Hiroshi*; Hata, Kuniki; Sato, Tomonori; Kaji, Yoshiyuki; Inoue, Hiroyuki*; Taguchi, Mitsumasa*; Seito, Hajime*; Tada, Eiji*; et al.

Zairyo To Kankyo, 69(4), p.107 - 111, 2020/04

https://doi.org/10.3323/jcorr.69.107

To evaluate the effect of oxidants, which are formed by radiolysis of water under gamma ray irradiation, on the corrosion of a carbon steel in humid environment, ozone was introduced as a model oxidant in to humidity-controlled air at 50C in a thermo-hygrostat chamber. Corrosion monitoring was performed by using an Atmospheric Corrosion Monitor-type (ACM) sensor consisting of a carbon steel anode and an Ag cathode. The output current of the ACM sensor was increased with the increase in relative humidity and it was obviously increased with the increase in the introduced ozone concentration at each relative humidity. The results indicate that ozone accelerates the corrosion of the carbon steel. The effect of ozone on the corrosion acceleration is attributed to the fast reduction reaction and fast dissolution reaction in to water compared to that of oxygen.

Diffusion behavior of DO in FeO film on Fe formed in an NaOH solution containing oxidants

Haruna, Takumi*; Miyataki, Yuki*; Hirohata, Yohei*; Shibata, Toshio*; Taniguchi, Naoki; Tachikawa, Hirokazu*

Zairyo To Kankyo, 67(9), p.375 - 380, 2018/09

This research aimed to confirm the formation of FeO film on Fe immersed in aqueous 45 mass% NaOH solution containing some oxidants at the boiling temperature, to recognize the optimum immersion time for the formation of thick and protective film, and to reveal the absorption behavior of DO in the FeO film at room temperature. The results were obtained as follows. It was confirmed that FeO film was formed on Fe immersed in the NaOH solution for a time more than 0.6 ks, and the film thickness increased parabolically with an increase in the immersion time. DO absorption test was carried out to the films formed in the NaOH solution for immersion times of 1.2 and 3.6 ks. An amount of DO absorbed into the film increased with an increase in an absorption time up to 1000 ks, and an absorption time more than 1000 ks made an amount of DO constant. The constant amount of DO was larger for the film formed on Fe immersed in the NaOH solution for 3.6 ks than that for 1.2 ks. The transient of the amount of DO absorbed into the film was analyzed on the basis of Fick's law for diffusion, and diffusion coefficients of DO were obtained to be 5.110 cm s and 9.910 cm s for the films formed for 1.2 and 3.6 ks, respectively. Therefore it was estimated that the diffusion coefficient of the FeO film was in the region from 5.110 cm s to 9.910 cm s.

Effect of chloride concentration on corrosion behavior of carbon steel under -ray irradiation

Motooka, Takafumi; Ueno, Fumiyoshi

Zairyo To Kankyo, 64(6), p.220 - 223, 2015/06

http://doi.org/10.3323/jcorr.64.220

Corrosion behavior of carbon steel in chloride aqueous solutions under a low dose rate was investigated by corrosion test using chloride aqueous solutions with different chloride concentration at a dose rate of 500 Gy/h. The corrosion rate of carbon steel increased by the irradiation, and the corrosion rate had the maximum value at a certain chloride concentration. The oxidants produced by radiolysis of chloride aqueous solution enhanced the corrosion of carbon steel. The main oxidants were oxygen and hydrogen peroxide, and the diffusion process of oxidants controlled the corrosion of carbon steel under irradiation. There was a positive correlation between the dependence of corrosion rate and chloride concentration and the dependence of oxidant concentration and chloride concentration.

Passivation condition of carbon steel in bentonite/sand mixture

Taniguchi, Naoki; Kawakami, Susumu; *

JNC-TN8400 2001-025, 27 Pages, 2002/03

JNC-TN8400-2001-025.pdf:0.82MB

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.

The Activity of sulfate reducing bacteria in bentonite and the effect of hydrogen sulfide on the corrosion of candidate materials for overpacks

Taniguchi, Naoki; Kawasaki, Manabu*; Fujiwara, Kazuo*

JNC-TN8400 2001-011, 62 Pages, 2001/03

JNC-TN8400-2001-011.pdf:6.42MB

The corrosion of metallic materials used in natural environment are sometimes affected by microbial action. It is apprehended that microorganism living in deep underground or brought from ground surface during excavation makes an impact on overpack material for geological disposal of high-level radioactive waste. Sulfate reducing bacteria (SRB) is known to be one of the most representative microorganism which affects the corrosion of metals. In this study, the behavior of growth of SRB was investigated at first under the presence of bentonite as a main component of buffer material which encloses the overpack. The results of the tests showed that the population of SRB after the culture in synthetic sea water mixed with bentonite decreased with increasing the ratio of bentonite/solution. SRB was hardly grown in medium whose bentonite/solution ratio exceeded 1000g/l. As a conservative case, the effects of sulfide on the corrosion of overpack materials were also studied assuming high activity of SRB. Carbon steel, copper and titanium specimens were immersed in synthetic sea water purging 0.1MPa HS gas and the corrosion behavior was compared with the results in N gas purging environment. Obvious effect of sulfide on the corrosion of carbon steel was not observed, but the corrosion rates of copper specimens were accelerated several hundred times by purging HS gas. The absorption of hydrogen into titanium specimens was not affected by purging HS gas, but the difference of hydrogen absorption between pure titanium and titanium alloy containing 0.06%-Pd was observed.

Sodium pooI combustion Test (Run-F7-3 and Run-F8-1) to confirm the condition of floor liner's corrosion

; ; Ohno, Shuji;

JNC-TN9400 2000-092, 247 Pages, 2000/08

JNC-TN9400-2000-092.pdf:20.29MB

Small-scale sodium pool combustion tests Run-F7-3 and Run-F8-1 were performed to investigate the corrosion of floor liner under high moisture condition. ln the both tests, which were performed using the 3m FRAT-1 vessel at the SAPFIRE facility, the sodium of 507deg-C was leaked on the carbon steel catch pan about for 25 minutes with the flow rate of around 25 kg/h. The air in the vessel was ventilated with the flow rate of 5m/min containing the moisture of 25000-28000 vol.ppm. The duration of combustion was different in two tests by changing the starting time of argon gas injection into the vessel. As the results of post-test analysis such as observation of catch pan surface and chemical analysis of the deposits, it was confirmed that 'Na-Fe double oxidization type corrosion' was dominant in the both tests and that the catch pan and deposits were not under the condition leading to the occurrence of 'molten salt type corrosion.'

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:2.01MB

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 (FeO) based for the outer layer and magnetite (FeO) based for the inner layer. And for the last steel, it had three (3) layer in the rust as hematite (FeO) based for the outer layer, magnetite (FeO) 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.

None

Shibata, Toshio*; *; *; Tsuru, Toru*; Inoue, Hiroyuki*

JNC-TJ8400 2000-013, 38 Pages, 2000/02

JNC-TJ8400-2000-013.pdf:3.25MB

None

Inspection about the corrosion of metallic archaeological artifacts in ground

Honda, Takashi*; *

JNC-TJ8400 2000-007, 200 Pages, 2000/02

JNC-TJ8400-2000-007.pdf:14.84MB

In general, it is very difficult to evaluate the residual state of metallic iron and the original shape of iron-base archaeological artifacts, as these are covered by thick oxide films formed in the ground during over several hundred years. The purpose of this research is to quantify the corrosion of an artifact such as base, knife, and nail, which was digged out of the relics about 500-1,000 years old. (1)The outer oxide film layer and the inner metallic iron can be quantitatively divided by using X-ray CT method. Furthermore, the original surfaces of artifacts can be estimated from the obtained images, even if the metallic iron has corroded completely. The X-ray CT images were also compared with those obtained by X-ray transmission inspection. (2)The corrosion amounts and rates were evaluated on the basis of thicknesses, densities, and iron concentrations of oxide films. (3)The characteristic differences between ancient iron and modern carbon steel were evaluated by analyzing the ancient iron slag.

Trial manufacturing of copper-carbon steel composite overpack

*; *; Tanai, Kenji

JNC-TN8400 99-049, 94 Pages, 1999/11

JNC-TN8400-99-049.pdf:6.63MB

This paper reports the results of design analysis and trial manufacturing of copper-carbon steel composite overpacks. The overpack is one of the key components of the engineered barrier system, hence, it is necessary to confirm the applicability of current technique in their manufacture. The Copper-Carbon steel composite overpack consists of a double container, an outer vessel made of oxygen-free, high-purity copper as the corrosion allowance material, and an inner vessel made of carbon steel as the pressure-resistant material. The trial manufacturing in this time, only the copper outer vessel has been fabricated. Both oxygen-free copper and oxygen-free phosphorus copper were used as materials for the outer vessel. For the shell and bottom portion, these materials were formed integrally by a backward extrusion method. For sealing the top cover plate to the main body, an electron-beam welding method was applied. After manufacturing, mechanical testing of specimens from the copper vessels were carried out. It was confirmed that current technique has sufficient feasibility to manufacture outer vessel. In addition, potential for irradiation embrittlement of the inner carbon-steel vessel by irradiation from vitrified waste over the life time of the overpack has been analyzed. It was shown that the small degree of irradiation embrittlement gives no significant impact on the pressure resistance of the carbon-steel vessel. Future research and development items regarding copper-carbon steel composite overpacks are also discussed.