Development of an electrochemical measurement method for carbon steels in radiation source dissolved solution and a corroded specimen analysis method using an imaging plate

Yamashita, Naoki; Aoyama, Takahito; Kato, Chiaki; Sano, Naruto; Tagami, Susumu

JAEA-Technology 2023-028, 22 Pages, 2024/03

JAEA-Technology-2023-028.pdf:1.9MB

At the Fukushima Daiichi Nuclear Power Station (1F), which is currently undergoing decommissioning, there is growing interest in the effects of radiation-emitting radionuclides such as Sr and Cs on the structural integrity. In particular, the corrosion behavior of carbon steel, which is used in many parts of 1F, is known to change depending on metal cations in solution, but the effects of Sr and Cs on corrosion are not yet understood. In addition, it is important to investigate the distribution of Sr and Cs in the rust layer in order to understand the corrosion behavior, but the method has not yet been established. In this study, a glove box was prepared to conduct corrosion tests of carbon steel in NaCl containing Sr and Cs in the glove box. In addition, in order to clarify the influence of Sr and Cs, which exist as metal cations in the solution, on the corrosion behavior of carbon steel, we attempted to establish a detection method for radioactive materials in the rust layer using an imaging plate.

Development of a test method for electrochemical measurements of stainless steel in nitric acid solution containing neptunium-237 under gamma-ray irradiation

Yamashita, Naoki; Irisawa, Eriko; Kato, Chiaki; Sano, Naruto; Tagami, Susumu

JAEA-Technology 2022-035, 29 Pages, 2023/03

JAEA-Technology-2022-035.pdf:2.54MB

In the treatment process of the current commercial reprocessing plant (Rokkasho Reprocessing Plant), the high-level liquid waste concentrator is the equipment that treats the most corrosive solution. In the high-level liquid waste concentrator, the extracted liquid waste after separation of uranium and plutonium is heated, concentrated, and reduced in volume. Therefore, the amount of gamma- rays emitted from fission products and the concentration of corrosive metal ion species such as neptunium-237 (Np) are the highest in the reprocessing process, and the amount of corrosion in the high-level liquid waste concentrate canner is expected to be large. In this study, in order to clarify the effect of gamma-rays on the corrosion reaction of stainless steel in nitric acid solutions containing Np from the electrochemical viewpoint, the corrosion test apparatus for heat transfer surfaces in an airtight concrete cell at the Waste Safety TEsting Facility (WASTEF) of Nuclear Science Research Institute was modified to enable electrochemical measurements under gamma-ray irradiation. The effect of gamma-rays on the corrosion reaction taking place on the stainless steel surface was discussed from the electrochemical test results obtained. As a result, changes in the immersion potentials of stainless steel and the polarization curves due to chemical species caused by radiolysis of gamma-ray irradiation were confirmed.

Electrochemical behavior of Fe-Cr-Ni alloys in simulated crevice condition in high temperature water

Soma, Yasutaka; Kato, Chiaki

Zairyo To Kankyo 2022 Koenshu (CD-ROM), p.219 - 220, 2022/05

It is important to understand the electrochemical properties of stainless steel in environment created within crevice of stainless steel in high temperature water (crevice environment). This is because acidification and concentration of impurity ions occur in the crevice environment and this is common inside the stress corrosion crack. In this study, we reproduced the crevice environment in bulk scale and investigated mainly the effect of Cr concentration on the electrochemical properties of Fe-Cr-Ni alloys. Polarization curves of Fe-20Ni-xCr (x=16.4, 23, 26) were measured in water with a temperature of 288C, a Cl concentration of 210 mol/dm, a pH value of about 4.5, and a dissolved hydrogen concentration of 10 ppb. The peak currents of active dissolution (at -400 mV) and passive current density (at -50 mV) for specimens with Cr concentrations x = 16.4, 23, and 26% were approximately 13.8, 15.9, 10.0 Acm, and 18.4, 8.5, 8.5 Acm, respectively. Although the current values of x=26 were slightly lower in both cases, it was concluded that there was no clear dependence of the polarization curve on Cr concentration in this environment.

Effect of Sr dissolved solution on corrosion potential of type 316L stainless steel

Aoyama, Takahito; Kato, Chiaki; Sato, Tomonori; Sano, Naruto; Yamashita, Naoki; Ueno, Fumiyoshi

Zairyo To Kankyo, 71(4), p.110 - 115, 2022/04

https://doi.org/10.3323/jcorr.71.110

no abstracts in English

Effect of oxygen concentration on corrosion rate of carbon steel in air/solution alternating condition

Otani, Kyohei; Ueno, Fumiyoshi; Kato, Chiaki

Zairyo To Kankyo, 71(2), p.40 - 45, 2022/02

The purpose of this study is to investigate the effect of oxygen concentration in the air on the corrosion rate of carbon steel in an air/solution alternating environment in the low oxygen concentration range and to clarify the corrosion rate and corrosion mechanism of carbon steel depending on the oxygen concentration in air by the mass change of specimens before and after the corrosion test and observing the iron rust layer formed on the surface of carbon steel. The corrosion rate increases with increasing oxygen concentration in the air, and the gradient of the corrosion rate decreases gradually. The maximum erosion depth increased with increasing oxygen concentration except for the case of 1% oxygen concentration, however, the maximum erosion depth for 1% oxygen concentration was larger than that for 5% air oxygen concentration.

Corrosion of carbon steel in the simulated air/solution interface environment

Otani, Kyohei; Kato, Chiaki

Zairyo To Kankyo, 70(12), p.480 - 486, 2021/12

https://doi.org/10.3323/jcorr.70.480

This is a comprehensive paper of the corrosion of carbon steel in air/solution alternating condition. From cross-sectional observation and analysis of the iron rust layer formed on the surface of carbon steel in the alternating condition, it was found that a multilayered iron rust layer composed of red rust layer (-FeOOH), rust crust layer (FeO), inner crystal (FeO), and inner rust layer was formed on carbon steel. The multi-layered iron rust layer would accelerate the cathodic oxygen reduction reaction, and the reason why the corrosion rate of the carbon steel in the alternating condition was accelerated. The effect of artificial seawater (ASW) composition on the corrosion rate of carbon steel in air/solution alternating condition was investigated. It was found that the corrosion rate increased with increasing concentration from pure water to 200 times diluted ASW, and decreased with increasing concentration from 20 times diluted ASW to no diluted ASW. The Mg and Ca ions in ASW precipitated on the reaction interface and formed a metal cation layer, which inhibited the oxygen reduction reaction, and thus the corrosion of carbon steel was inhibited in the highly concentrated ASW.

Development of atmospheric corrosion model considering meteorological data and airborne sea salt

Igarashi, Takahiro; Komatsu, Atsushi; Kato, Chiaki; Sakairi, Masatoshi*

Bosei Kanri, 65(10), p.365 - 370, 2021/10

We have developed a new atmospheric simulation model considering important environmental factors such as airborne sea salt, temperature, relative humidity, and rainfall. The developed model was verified by comparing predicted values by the simulation and measured data for the weight loss by atmospheric corrosion. In addition, atmospheric corrosion simulations under open and sheltered exposure condition were conducted, and it was confirmed that the air corrosion weight loss was strongly suppressed by the surface cleaning effect due to rainfall.

Hydrogen absorption mechanism into iron in aqueous solution including metal cations by laser ablation tests and first-principles calculations

Igarashi, Takahiro; Otani, Kyohei; Kato, Chiaki; Sakairi, Masatoshi*; Togashi, Yusuke*; Baba, Kazuhiko*; Takagi, Shusaku*

ISIJ International, 61(4), p.1085 - 1090, 2021/04

https://doi.org/10.2355/isijinternational.ISIJINT-2020-065

In order to clarify the effect of metal cations (Zn, Mg, Na) in aqueous solution on hydrogen permeation into iron, the amount of hydrogen permeation from iron surface was measured by electrochemical tests with a laser ablation. Moreover, in order to obtain the basic mechanism of hydrogen permeation with metal cation, first-principles calculations were used to acquire the adsorption potential of the metal cation and the electronic state around iron surface. By Zn in solution, anodic reaction on ablated surface by laser irradiation was suppressed. Also, by quantum analysis Zn atoms were chemically bonded stronger than Na and Mg atoms to iron surface. It was suggested that the dissolution reaction of iron was suppressed by the formation of the Zn layer, and that lead suppression of hydrogen permeation into iron.

Effect of seawater components on corrosion rate of steel in air/solution alternating condition

Otani, Kyohei; Tsukada, Takashi; Ueno, Fumiyoshi; Kato, Chiaki

Zairyo To Kankyo, 69(9), p.246 - 252, 2020/09

https://doi.org/10.3323/jcorr.69.246

The purpose of this study was to investigate the effect of artificial sea water concentration on the corrosion rate of carbon steel under air/solution alternating condition, and to clarify the corrosion mechanism of carbon steel that changes with artificial seawater concentration. Mass measurements showed that the corrosion rate of carbon steel in the alternating condition accelerates with increasing concentration in the concentration region between deionized water to 200 times diluted artificial seawater (ASW), and the corrosion rate decreases with increasing concentration in the concentration region between 20 times diluted ASW to undiluted ASW. It can be considered that the reason why the carbon steel corrosion was suppressed in highly concentrated artificial seawater would Mg ions and Ca ions in the artificial seawater precipitate and cover on the surface due to the increase in pH near the surface by oxygen reduction reaction.

Modelling of intergranular corrosion using cellular automata, 1; Characteristics and corrosion rates of stainless steels in modified nuclear reprocessing solution

Yamamoto, Masahiro; Irisawa, Eriko; Igarashi, Takahiro; Komatsu, Atsushi; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2019) (Internet), 5 Pages, 2019/09

Intergranular corrosion phenomena were analysed using modified reprocessing solution. The data indicated that corrosion rates increased with time at the initial stage, and these stayed at constant value. Intergranular corrosion propagated at grain boundary in the initial stage and then attacked whole grain boundary causing drop out of grains. Corrosion rates of steady state were sum of intergranular corrosion amounts and weight losses of dropped grains. Surface appearances and cross sections of corroded samples were analyzed. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. These ratios differed from individual grain boundaries. Total corrosion rates were affected by the distribution of these ratios. These data were based on the numerical modelling of intergranular corrosion using cellular automata. And also, calculated results were compared with these analytical data.