Development of a hybrid evaluation method for long-term structural soundness of nuclear reactor buildings using monitoring and damage imaging technologies; Nuclear energy science & technology and human resource development project

Maeda, Masaki*; Tanabe, Tadao*; Nishiwaki, Tomoya*; Aoki, Takayuki*; Dozaki, Koji*; Nishimura, Koshiro*; Fujii, Sho*; Ueno, Fumiyoshi; Tanaka, Akio*; Suzuki, Yusuke*; et al.

Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03

Effects of potential on the electrical conductivity of a solution within a crevice of stainless steel in high-temperature water

Soma, Yasutaka; Komatsu, Atsushi; Ueno, Fumiyoshi

Corrosion, 78(6), p.503 - 515, 2022/06

https://doi.org/10.5006/3187

The effects of electrochemical potential (ECP) on water chemistry within a crevice are of critical importance for understanding stress corrosion cracking (SCC) of Fe-Cr-Ni alloys in high temperature water. In this study, the effects of ECP on the electrical conductivity of a solution within a Type-316L stainless steel crevice () have been studied in 288C and 8 MPa water containing 10 ppb Cl as major anionic species. In situ measurements of in a rectangular crevice with a gap of 15 m and a depth of 23 mm have been conducted using small sensors installed at different crevice depths. An increase in ECP from -0.49 V (vs. standard hydrogen electrode) to -0.12 V resulted in an increase in from 12 Scm to 160 Scm at a distance of 21 mm from the crevice mouth. The increase in reached a maximum at about 0.15 V (about 300 Scm) and then tended to decrease with increasing potential. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. It is considered that Cl is the major anionic species transported into the crevice at relatively low potentials, and that increases monotonically with increasing ECP. On the other hand, when ECP exceeds around 0 V, a sufficient amount of HCrO generated by transpassive dissolution also transported into the gap. Since this chemical species is highly oxidizing, unlike Cl, it is assumed that it reacts with metal cations to oxidize and precipitate them, thereby lowering conductivity.

Time dependence of corrosion behavior on Ta in NaOH solutions

Ishijima, Yasuhiro; Ueno, Fumiyoshi; Abe, Hitoshi

Materials Transactions, 63(4), p.538 - 544, 2022/04

https://doi.org/10.2320/matertrans.MT-C2021005

The time dependence of the corrosion behavior of tantalum (Ta), which is used in nuclear fuel reprocessing equipment, in sodium hydroxide (NaOH) solutions was investigated by immersion tests, and the mechanism of the time dependence was examined via surface observations and electrochemical measurements. The immersion tests were conducted at room temperature with NaOH concentrations ranging from 1 to 7 mol/L for immersion periods of 24 to 168 h. The corrosion rate increased with the NaOH concentration but peaked with the immersion period and then decreased. The time to peak of the corrosion rate was shorter with higher NaOH concentration. The X-ray diffraction (XRD) patterns and Raman spectra of the surfaces of the specimens immersed in the 7 mol/L NaOH solution for more than 48 h showed NaTaO formation. The polarization resistance decreased with immersion time for all NaOH concentrations up to about 24 h after immersion. Thereafter, the polarization resistance increased with immersion time in 7 mol/L NaOH solution and remained almost constant in the other NaOH concentrations. Findings suggested that the change in the corrosion rate was affected by the film formation during immersion, since the time dependence of the polarization resistance and the sum of film resistance and charge transfer resistance had the same tendencies. The precipitation film was mainly NaTaO formed by the dissolution of the passivity film on Ta.

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

Novel strain induces severe corrosion by retrieving electrons from Fe under a freshwater environment

Hirano, Shinichi*; Ihara, Sota*; Wakai, Satoshi*; Dotsuta, Yuma; Otani, Kyohei; Kitagaki, Toru; Ueno, Fumiyoshi; Okamoto, Akihiro*

Microorganisms (Internet), 10(2), p.270_1 - 270_12, 2022/02

https://doi.org/10.3390/microorganisms10020270

To understand the role of methanogens in corrosion under anoxic conditions in freshwater, we investigated the corrosion activities of methanogens in samples collected from groundwater and rivers. We enriched microorganisms that can grow with CO/NaHCO and Fe as the sole carbon source and electron donor, respectively, in ground fresh water. Electrochemical analysis revealed that strain can uptake electrons from the cathode at lower than -0.61 V vs SHE and has a redox-active component with electrochemical potential different from those of other previously reported methanogens with extracellular electron transfer ability. This study indicated the corrosion risk by methanogens capable of taking up electrons from Fe in anoxic freshwater environments and the necessity of understanding the corrosion mechanism to contribute to risk diagnosis.

A Task of microbiologically influenced corrosion in Fukushima Daiichi Decommissioning

Wakai, Satoshi*; Hirano, Shinichi*; Ueno, Fumiyoshi; Okamoto, Akihiro*

Zairyo To Kankyo, 70(12), p.491 - 496, 2021/12

https://doi.org/10.3323/jcorr.70.491

After Fukushima Daiichi Nuclear Power Station accident, various corrosion mitigating activities have been treated, and severe corrosion incident have never taken placed. On the other hand, the facilities were exposed sea water, and some of them have continuously exposed to ground water. The exposure of metal materials to environmental water has a risk of microbiologically influenced corrosion (MIC). In this paper, we summarize the latest knowledge of MIC and the task of MIC in the decommissioning of Fukushima Daiichi Nuclear Power Station.

Three-dimensional computational modeling and simulation of intergranular corrosion propagation of stainless steel

Igarashi, Takahiro; Komatsu, Atsushi; Motooka, Takafumi*; Ueno, Fumiyoshi; Yamamoto, Masahiro

Corrosion Science and Technology, 20(3), p.105 - 111, 2021/06

https://doi.org/10.14773/CST.2021.20.3.105

We constructed three dimensional computational model using cellular automata method to simulate the intergranular corrosion propagation of stainless steel. In the model, the computational system was constructed by three types of cells: grain (bulk), grain boundary (GB), and solution cell. Our simulations revealed that the surface roughness calculated by the model adopted distributed dissolution rates of GBs was greater than that adopted constant dissolution rates of GBs. The cross-sectional images obtained by our simulation were comparable with that obtained by corrosion tests. These results indicate that the surface roughness during corrosion relates the distribution of corrosion rate.

Time dependence of corrosion behavior on Ta in NaOH solutions

Ishijima, Yasuhiro; Ueno, Fumiyoshi; Abe, Hitoshi

Zairyo To Kankyo, 70(6), p.192 - 198, 2021/06

https://doi.org/10.3323/jcorr.70.192

The time dependence of corrosion behavior on tantalum used in nuclear fuel reprocessing equipment in sodium hydroxide solution was investigated by immersion corrosion tests, and the mechanism of aging change was discussed from surface observations and electrochemical measurements. The immersion tests were carried out at room temperature with NaOH concentrations ranging from 1 to 7 mol/L and immersion times ranging from 24 to 168 hr, respectively. The corrosion rate increased with NaOH concentration, but peaked with immersion time and then decreased. The time to peak of corrosion rate was shorter with higher NaOH concentration. The SEM observations and Raman analysis at the surface of the specimens that were cleaned and weighed after the immersion test did not show any film formation. On the other hand, the polarization resistance showed a constant value or an increase after a decrease immediately after immersion. It is suggested that the change in corrosion rate is affected by the formation of film by immersion, since the value of polarization resistance is almost the same as the sum of film resistance and charge transfer resistance. The film was considered to be mainly NaTaO formed by the dissolution of Ta.

Consideration on stress corrosion cracking evaluation of zirconium for Fuel Reprocessing Facilities

Hashikura, Yasuaki*; Ishijima, Yasuhiro; Nakahara, Masaumi; Sano, Yuichi; Ueno, Fumiyoshi; Abe, Hitoshi

Hozengaku, 19(3), p.95 - 102, 2020/10

A plutonium concentrator was selected, and constant load tensile tests with controlled applied potentials and electrochemical tests were conducted in nitric acid and sodium nitrate solutions. From the results, a map which shows the effect of nitric acid concentration to crack initiation potential was drawn. And, it was pointed out that not only the nitric acid but also the nitrate ion coordinated to the nitrate must be considered in evaluating the possibility of stress corrosion cracking.

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.