Otani, Kyohei; Tsukada, Takashi; Ueno, Fumiyoshi
Zairyo To Kankyo, 68(8), p.205 - 211, 2019/08
In the present study, the iron rust layer formed on the low ally steel in air-solution alternating condition was investigated by cross-sectional observation and analysis, and the mechanism of accelerated corrosion of the steel in the alternating condition was clarified. Observation and analysis showed that the multi-layered iron rust layer composed of red rust layer (FeOOH), rust crust layer (FeO), inner crystal (FeO), and inner rust layer was formed on the low alloy steel. It can be considered that the multi-layered iron rust layer accelerated the cathodic reaction rate of the steel in the alternating condition. This acceleration would be the reason why the corrosion rate of the low alloy steel in the alternating condition was accelerated.
Hata, Kuniki; Inoue, Hiroyuki*; Kojima, Takao*; Kasahara, Shigeki; Hanawa, Satoshi; Ueno, Fumiyoshi; Tsukada, Takashi; Iwase, Akihiro*
Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2017 (AWC 2017) (USB Flash Drive), p.304 - 314, 2017/09
A model simulation of radiolysis of mixed solutions of NaCl and NaBr was carried out. The simulation result agreed well with the experimental result, and Br played an important role in determining the amounts of products from water radiolysis. The simulation result also showed that, in highly pure NaCl solutions, the steady-state concentration of a radolytic product, HO, was mainly controlled by three reactions (Cl + OH ClOH, ClOH Cl + OH, and ClOH + H Cl + HO), which indicated that accurate evaluation of the rate constants of these reactions was very important in improving the radiolysis simulation of solutions containing Cl. An immersion test using a low-alloy steel, SQV2A, in the mixed solutions was also carried out under irradiation. The corrosion rate increased or decreased depending on the pH or the concentrations of the halide ions in a similar way to the change in concentration of HO produced from water radiolysis, which is affected by the presence of Cl and Br. However, at high pH values (12), the corrosion rate was almost zero even though the concentration of HO was high. This could be attributed to enhancement of the passivity of test specimens at higher pH values.
Fukui, Toshiki*; Maki, Takashi*; Miura, Nobuyuki; Tsukada, Takeshi*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 23(2), p.169 - 173, 2016/12
The basic research programs for the next generation vitrification technology, which are commissioned project from Ministry of Economy, Trade and Industry of Japan, have been implemented from 2014 until 2018 for developing the advanced vitrification technology of low level wastes and high level liquid wastes.
Hata, Kuniki; Sato, Tomonori; Motooka, Takafumi; Ueno, Fumiyoshi; Hanawa, Satoshi; Kasahara, Shigeki; Tsukada, Takashi
Journal of Nuclear Science and Technology, 53(8), p.1183 - 1191, 2016/08
Hata, Kuniki; Inoue, Hiroyuki*; Kojima, Takao*; Iwase, Akihiro*; Kasahara, Shigeki; Hanawa, Satoshi; Ueno, Fumiyoshi; Tsukada, Takashi
Nuclear Technology, 193(3), p.434 - 443, 2016/03
Komatsu, Atsushi; Tsukada, Takashi; Ueno, Fumiyoshi; Yamamoto, Masahiro
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 4 Pages, 2015/05
Effect of oxygen and hydrogen peroxide on corrosion rate of carbon steel in diluted artificial seawater was investigated by electrochemical methods. Diffusion coefficient and thickness of diffusion layer for oxygen and hydrogen peroxide were measured to estimate the diffusion limiting current density. Corrosion tests of carbon steel were also conducted in diluted artificial seawater containing oxygen and/or hydrogen peroxide at 323K. The diffusion coefficient of hydrogen peroxide was about 0.8 times lower than that of oxygen, and the thickness of diffusion layer was almost equivalent between oxygen and hydrogen peroxide. Diffusion limiting current density of hydrogen peroxide was estimated to be 0.4 times lower than that of oxygen in the same concentration at 323K. Plot of corrosion rate with the addition of concentration of oxygen and 0.4 times concentration of hydrogen peroxide showed good correlation.
Motooka, Takafumi; Komatsu, Atsushi; Tsukada, Takashi; Yamamoto, Masahiro
JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 18, 2015/03
The effect of changes in water by -ray irradiation on the pit initiation of Zircaloy-2 in artificial seawater was investigated. Surface analysis and electrochemical test were conducted. They showed that the hydrogen peroxide produced by irradiation forms a passive film and the passive film is resistant to the pit initiation.
Hata, Kuniki; Hanawa, Satoshi; Motooka, Takafumi; Tsukada, Takashi
JAEA-Review 2014-050, JAEA Takasaki Annual Report 2013, P. 22, 2015/03
Fukushima Daiichi Nuclear Power Plants experienced seawater injection into the cores and spent fuel pools as an emergent measure for a short period after the accident. The injected seawater was exposed to radiation, and radiolytic species were produced. Especially, hydrogen peroxide (HO) is known as an oxidant which affects corrosion of materials. In order to identify the important factor which results in the high concentration of HO in seawater radiolysis, the concentrations of HO in -irradiated artificial seawater was measured and compared with the result of radiolysis calculation. Solutions containing some constituents of seawater were also measured to identify which ion affects HO production of seawater radiolysis. The experimental results showed that the HO production from seawater radiolysis is mainly attributed to reactions of Cl and Br in water radiolysis, though many kinds of ions are dissolved in seawater.
Sato, Tomonori; Yamamoto, Masahiro; Tsukada, Takashi; Kato, Chiaki
Zairyo To Kankyo, 64(3), p.91 - 97, 2015/03
In the boiling water reactors (BWRs), reactor cooling water is maintained in high purity condition by controlling of a deionizing and deaerating apparatus, however HO contains by water radiolysis. In order to determine the corrosive condition in high-temperature pure water containing HO, the electrochemical impedance spectroscopy was performed in this study. To simulate BWR condition precisely, the measurements were performed without any electrolyte. The obtained impedance responses were changed with the HO concentration. The solution resistance and polarization resistance were determined by the equivalent circuit analyses. The conductivity was determined by the obtained solution resistance and the calculation of the current flow between the working electrode and the counter electrode by the 3-demensional finite element method. The value, 4.410 S/cm, was obtained as the conductivity of the pure water at 288C. The reciprocal of the obtained polarization resistance increased in proportion with HO concentration. This indicates that the corrosion current density was determined by the diffusion limiting current density of HO. The diffusion coefficient of HO at 288C was determined using the relationship between the reciprocal of the polarization resistance and HO concentration. The obtained diffusion coefficient was 1.510 cm/s. This is about twice larger than that of the reported value of O.
Yamamoto, Masahiro; Nakano, Junichi; Komatsu, Atsushi; Sato, Tomonori; Tsukada, Takashi
Proceedings of 19th International Corrosion Congress (19th ICC) (CD-ROM), 6 Pages, 2014/11
Corrosion protection of RPV and PCV is an important issue for the long term maintenance until the end of the decommissioning procedures. One of the uncertain factors for the issue is an effect of radioactivity on corrosion of LAS and CS. Corrosion tests using LAS and CS were conducted in -rays irradiated condition. Oxygen and hydrogen peroxide concentrations in the water were measured after the tests. Corrosion test results indicated that the amounts of corrosion increased by -rays irradiation both air and nitrogen atmosphere. And also corrosion amounts increased with -ray dose rates. Electrochemical analyses indicated that cathodic reaction of Hydrogen peroxide was controlled by diffusion process. The measured diffusion constant of HO was about 0.75 times to that of oxygen. From these results, it is estimated that corrosion of LAS and CS in -ray irradiated condition was evaluated by the cathodic reduction reaction of oxidant.
Motooka, Takafumi; Tsukada, Takashi
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
In Fukushima Daiichi Nuclear Power Station (1F), seawater was injected into spent fuel pools in March 2011. Zircaloy-2 is adopted for the fuel cladding at 1F. Zirconium alloys including Zircaloy-2 are susceptible to pitting corrosion in oxidizing chloride solutions. In this study, we investigated the effect of oxide film formed during -ray irradiation on pitting corrosion of fuel cladding in water containing sea salt. The pitting potentials of Zircaloy-2 were measured using the water containing artificial sea salt. Changes in the composition of water containing sea salt were analyzed before and after -ray irradiation. The characteristics of the oxide films formed on Zircaloy-2 were evaluated by X-ray photoelectron spectroscopy. Solution analyses for water containing sea salt showed that hydrogen peroxide was generated by the irradiation. The pitting potential of Ziracloy-2 with oxide film formed under -ray irradiation was higher than that with oxide film formed without irradiation. X-ray photoelectron spectroscopy indicated that the oxide film was composed of zirconium oxide and the growth of oxide film was enhanced during the irradiation. It could thus be explained that the enhanced growth of oxide film under -ray irradiation caused the higher pitting potential.
Yamamoto, Masahiro; Katayama, Hideki*; Sato, Tomonori; Tsukada, Takashi
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 6 Pages, 2014/10
In the Fukushima Dai-ichi Nuclear Power Plant, seawater and natural river water were poured for emergency cooling. Corrosion of materials was worried because of high chloride ion concentration from seawater. The chloride ion concentration was decreased by de-chlorination operation. However, the water was not treated in the viewpoint of microbial breeding, so that many microbes could be alive and microbially induced corrosion (MIC) was worried. So, we attempted to examine the ability of MIC occurrence by using of corrosion potential analysis. Corrosion potentials of samples rose to about 300 mV nobler than the initial values in the NB added solution. The potentials of the welded samples more easily rose than the simple plate. These potential changes are attributed to the biofilms formed on the sample surface. After about 100 days' immersion, evidence of localized corrosion was not observed. More immersion time is needed to clarify the MIC ability.
Nakano, Junichi; Kaji, Yoshiyuki; Yamamoto, Masahiro; Tsukada, Takashi
Journal of Nuclear Science and Technology, 51(7-8), p.977 - 986, 2014/07
Seawater was injected into the reactor cores in the Fukushima Daiichi Nuclear Power Station. Corrosion of reactor vessel steels is considered to progress. To evaluate durability of the reactor vessel steels, corrosion tests were conducted in diluted seawater at 50 C under -rays irradiation. 10 mg/L and 100 mg/L NH were added to diluted seawater. Without addition of NH, weight loss in the vessel steels irradiated with the 0.2 kGy/h dose rate was comparable with those without irradiation and weight loss in the vessel steels irradiated with the 4.4 kGy/h dose rate was higher than those without irradiation. Under irradiation, weight loss in the vessel steels in diluted seawater containing NH was comparable with that in diluted seawater without NH. When gas phase in the flask was replaced with N, weight loss in the vessel steels, and O and HO concentrations in the diluted seawater decreased.
Motooka, Takafumi; Komatsu, Atsushi; Tsukada, Takashi; Yamamoto, Masahiro
Journal of Nuclear Science and Technology, 51(7-8), p.987 - 995, 2014/07
Suzuki, Kazuhiro; Motooka, Takafumi; Tsukada, Takashi; Terakawa, Yuto; Ichise, Kenichi; Numata, Masami; Kikuchi, Hiroyuki
JAEA-Technology 2014-004, 29 Pages, 2014/03
By the effect of the Great East Japan Earthquake, seawater was injected into spent fuel pools in unit 2, 3 and 4 at Fukushima Daiichi Nuclear Plant in order to cool spent fuels. It is known that chloride ion contained in seawater could cause pitting corrosion for metallic materials. It was concerned that radioactive products inside of fuel cladding tubes might be escaped through the pits. Therefore we have investigated the pit initiation condition of fuel cladding tubes by measuring pitting potential in order to evaluate stability of the enclosure function of fuel cladding tubes in spent fuel pools containing sea salt. In this report, we describe the development of specimen preparation techniques for pitting measurement of spent fuel cladding tubes having high radioactivity. By accomplishing of the development of the specimen preparation techniques, we could evaluate pit initiation condition of spent fuel cladding tubes in water containing sea salt.
Nakano, Junichi; Yamamoto, Masahiro; Tsukada, Takashi
Nippon Genshiryoku Gakkai Wabun Rombunshi, 13(1), p.1 - 6, 2014/03
The seawater was injected into reactor cores of Units 1, 2 and 3 in the Fukushima Daiichi Nuclear Power Plant. To investigate effects of rays irradiation on corrosion of carbon steel and low alloy steel, corrosion tests were performed in the diluted seawater at 50 C under rays irradiation with dose rates of 4.4 kGy/h and 0.2 kGy/h. Hydrazine (NH) was added to the diluted seawater. In the diluted seawater without NH, the weight losses of the steels irradiated with 0.2 kGy/h were similar to those of the unirradiated steels, and the weight losses of the steels irradiated with 4.4 kGy/h increased to approximate 1.7 times of those of the unirradiated steels. The weight losses of the steels irradiated in the diluted seawater containing NH were similar to those in the diluted seawater without NH. When N was introduced to gas phase in the flasks during rays irradiation, the weight losses of the steels decreased.
Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Kaji, Yoshiyuki
Journal of Nuclear Materials, 444(1-3), p.454 - 461, 2014/01
Cracking growth tests were conducted in high-temperature water containing hydrogen peroxide (HO) at 561 to 423 K to evaluate the effects of HO on stress corrosion cracking (SCC) of stainless steel (SS) at temperature lower than the boiling water reactor (BWR) operating temperature. Small compact tension (CT) specimens were prepared from thermally sensitized type 304 SS. Despite the observation of only a small portion intergranular SCC (IGSCC) near the side groove of the CT specimen at 561 K in high-temperature water containing 100 ppb of HO, the IGSCC area expanded to the central region of the CT specimens at 423 and 453 K. Effects of HO on SCC appeared intensely at temperature lower than the BWR operating temperature. To estimate the environment in the cracks, outer oxide distribution on the fracture surface and fatigue pre-crack were examined by laser Raman spectroscopy and thermal equilibrium calculation was performed.
Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Kaji, Yoshiyuki
Journal of Nuclear Materials, 441(1-3), p.348 - 356, 2013/10
Crack growth tests were performed in high-temperature water containing hydrogen peroxide (HO) to evaluate the relationships between the crevice structure and HO on stress corrosion cracking (SCC) growth morphology of stainless steel (SS). Small compact tension (CT) specimens with different fatigue pre-crack lengths were prepared. 20300 ppb HO was injected into the high-temperature water at 561 K. Intergranular SCC (IGSCC) was observed only near the side grooves of the CT specimens. Owing to pre-crack shortening, the IGSCC area expanded to the central region of the CT specimens. The effects of HO on SS appeared intensely near the surfaces exposed to high levels of HO. The calculations for the percentage of HO remaining showed that the effects of HO flowed from both sides of the crack were more obvious than those flowed from the crack mouth.
Yamamoto, Masahiro; Kato, Chiaki; Sato, Tomonori; Nakahara, Yukio; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*
Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2013) (CD-ROM), 5 Pages, 2013/09
Major corrosion problems of light water reactor (LWR) which are represented by stress corrosion cracking are affected by dissolved oxygen (DO) concentration in feed water. Many corrosion tests were conducted with the parameter of DO values. Oxygen source of an actual LWR is radiolysis of cooling water and also HO is generated. The effect of these species created by water radiolysis to corrosion of structural material was not sufficiently examined. -ray irradiated experiments were conducted in high temperature water condition using type 316L stainless steels with crevice. The calculation of radiolysis products was not estimated by the effect of radiolysis products. From these results, much complicated reaction seemed to occur at the -ray irradiated crevice portion.
Uchida, Shunsuke; Hanawa, Satoshi; Nishiyama, Yutaka; Nakamura, Takehiko; Sato, Tomonori; Tsukada, Takashi; Kysela, J.*
Nuclear Technology, 183(1), p.119 - 135, 2013/07
In-pile loop experiments are one of the key technologies which can provide an understanding of corrosion behaviors of structural materials in nuclear power plants (NPPs). The experiments should be supported not only by reliable measurement tools to confirm corrosive conditions under neutron and ray irradiations but also by theoretical models for extrapolating the measured data to predict corrosion behaviors in NPPs. The relationships among electrochemical corrosion potential (ECP), metal surface conditions, exposure time and other environmental conditions have been determined from in situ measurements of corrosion behaviors of stainless steel specimens exposed to HO and O in high temperature water. Based on the relationships, a model to evaluate ECP of stainless steel was developed by coupling an electrochemical model and a double oxide layer model. Major conclusions obtained from the evaluation model are as follows. (1) The difference in ECP behaviors of the specimens exposed to HO and O were mainly from the thickness and developing rate of the inner oxide layers. (2) Calculated ECP behaviors, e.g., the different responses to HO and O and hysteresis and memory effects, agreed with the measured ones. (3) Neutron exposure might decrease ECP due to radiation-induced diffusion in the oxide layer. The ECP evaluation model will be applied to evaluation of corrosive conditions in the JMTR in-pile loop.