Kasahara, Shigeki; Chimi, Yasuhiro; Hata, Kuniki; Hanawa, Satoshi
Zairyo To Kankyo, 68(9), p.240 - 247, 2019/09
In order to study environment assisted cracking mechanism of stainless steel under BWR primary coolant condition, effects of applied load on oxidation in the vicinity of crack tips of CT specimens were evaluated. Loaded CT specimens were immersed in an aqueous condition at 290C as a simulated BWR coolant condition, and microstructural observation on oxide near the tips of pre-cracks was carried out. Oxide inner layers, which consisted of fine grain magnetite containing Fe and Cr were formed, and oxide outer layers consisting of large grains of FeO were observed to cover the inner layers. FEM analysis of stress and strain in the loaded CT specimen suggests that both of dislocations due to localized plastic deformation and elastic strain could play important roles to accelerate inner oxide formation in the vicinity of the crack tip of the specimens.
Uchida, Shunsuke; Chimi, Yasuhiro; Kasahara, Shigeki; Hanawa, Satoshi; Okada, Hidetoshi*; Naito, Masanori*; Kojima, Masayoshi*; Kikura, Hiroshige*; Lister, D. H.*
Nuclear Engineering and Design, 341, p.112 - 123, 2019/01
Improvement of plant reliability based on reliability-centered-maintenance (RCM) is going to be undertaken in NPPs. RCM is supported by risk-based maintenance (RBM). The combination of prediction and inspection is one of the key issues to promote RBM. Early prediction of IGSCC occurrence and its propagation should be confirmed throughout the entire plant systems which should be accomplished by inspections at the target locations followed by timely application of suitable countermeasures. From the inspections, accumulated data will be applied to confirm the accuracy of the code, to tune some uncertainties of the key data for prediction, and then, to increase their accuracy. The synergetic effects of prediction and inspection on application of effective and suitable countermeasures are expected. In the paper, the procedures for the combination of prediction and inspection are introduced.
Chimi, Yasuhiro; Sato, Kenji*; Kasahara, Shigeki; Umehara, Ryuji*; Hanawa, Satoshi
Proceedings of Contribution of Materials Investigations and Operating Experience to Light Water NPPs' Safety, Performance and Reliability (FONTEVRAUD-9) (Internet), 10 Pages, 2018/09
To investigate the influence of Zinc (Zn) injection on primary water stress corrosion cracking (PWSCC) growth behavior, crack growth tests of 10% cold-worked Alloy 600 were performed in simulated primary water environment of pressurized water reactor (PWR) at 320C with a low-concentration (5-10 ppb) Zn injection under dissolved hydrogen (DH) conditions of 5, 30, and 50 cc/kgHO. As a result of the crack growth tests, DH-dependence of crack growth rate (CGR) showed a similar tendency to the predicted CGR based on the CGR data without Zn injection, indicating almost no effect of a low-concentration Zn injection on the crack growth behavior. Moreover, the microstructural analyses of oxide films formed inside the crack and on the specimen surface were conducted, and the intake of Zn in the oxides was detected on the specimen surface, but not detected inside the crack. This result was considered to be the cause of no Zn injection effect on the crack growth behavior.
Ha, Yoosung; Tobita, Toru; Takamizawa, Hisashi; Hanawa, Satoshi; Nishiyama, Yutaka
Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 6 Pages, 2018/07
Chimi, Yasuhiro; Iwata, Keiko; Tobita, Toru; Otsu, Takuyo; Takamizawa, Hisashi; Yoshimoto, Kentaro*; Murakami, Takeshi*; Hanawa, Satoshi; Nishiyama, Yutaka
JAEA-Research 2017-018, 122 Pages, 2018/03
Warm pre-stress (WPS) effect is a phenomenon that after applying a load at a high temperature fracture does not occur in unloading during cooling, and then the fracture toughness in reloading at a lower temperature increases effectively. Engineering evaluation models to predict an apparent fracture toughness in reloading are established using experimental data with linear elasticity. However, there is a lack of data on the WPS effect for the effects of specimen size and surface crack in elastic-plastic regime. In this study, fracture toughness tests were performed after applying load-temperature histories which simulate pressurized thermal shock transients to confirm the WPS effect. The experimental results of an apparent fracture toughness tend to be lower than the predictive results using the engineering evaluation models in the case of a high degree of plastic deformation in preloading. Considering the plastic component of preloading can refine the engineering evaluation models.
Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Okamoto, Yoshihiro; Shimoyama, Iwao; Honda, Mitsunori; Hanawa, Satoshi; Nishiyama, Yutaka
Photon Factory Activity Report 2017, 2 Pages, 2018/00
no abstracts in English
Uchida, Shunsuke*; Hanawa, Satoshi; Naito, Masanori*; Okada, Hidetoshi*; Lister, D. H.*
Corrosion Engineering, Science and Technology, 52(8), p.587 - 595, 2017/10
Based on the relationship among ECP, metal surface conditions, exposure time and other environmental conditions, a model to evaluate the ECP and corrosion rate of steel was developed by coupling a static electrochemical analysis and a dynamic oxide layer growth analysis. Major conclusion obtained on the model are as follows. The effect of HO and O concentrations on ECP were successfully explained as the effects of oxide layer growth. Hysteresis of ECP under changes in water chemistry conditions were successfully explained with the model. Decreases in ECP due to neutron exposure were explained well by radiation-induced diffusion in the oxide layers.
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.
Mukai, Satoru*; Umehara, Ryuji*; Hanawa, Satoshi; Kasahara, Shigeki; Nishiyama, Yutaka
Proceedings of 20th International Conference on Water Chemistry of Nuclear Reactor Systems (NPC 2016) (USB Flash Drive), 9 Pages, 2016/10
In Japanese PWR, the concentration of dissolved hydrogen in the primary coolant is controlled in the range from 25 cc/kg-HO to 35 cc/kg-HO for suppression of water decomposition. However this concentration is desired to reduce for the purpose of radiation source reduction in Japan. So, the concentration due to water radiolysis in primary coolant was evaluated at lower hydrogen concentration by the water radiolysis model in consideration of ray, fast neutron and alpha ray due to the reaction B(n,)Li. The results of evaluation showed that the water radiolysis was suppressed even if the hydrogen concentration was decreased to 5 cc/kg-HO. The effects of the different G-value and the rate constants of major reaction on the concentration of HO and O were studied under hydrogen addition. We also focused on the effect of the alpha radiolysis in boron acid water.
Hanawa, Satoshi; Uchida, Shunsuke; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki*; Nishiyama, Yutaka
Proceedings of 20th Nuclear Plant Chemistry International Conference (NPC 2016) (USB Flash Drive), 11 Pages, 2016/10
ECP is the exclusive index to evaluate corrosion condition directly at the points of interest in the mixing of neutron and -ray environment. ECP can be calculated through the combination of water radiolysis and ECP model. A water radiolysis model have been applied to experiments performed in in-pile loops in the experimental reactors and applicability was confirmed. An ECP model based on the Butler-Volmer equation was also prepared. ECP of stainless steel was measured under well controlled water chemistry condition in in-pile loop in the Halden reactor, and the model was applied to evaluate ECP measured in the Halden reactor. The measured data were well explained by the water radiolysis calculation and ECP model. Accumulation of in-pile ECP data are expected for further validation of the models.
Hanawa, Satoshi; Uchida, Shunsuke; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki*; Nishiyama, Yutaka
Proceedings of 20th Nuclear Plant Chemistry International Conference (NPC 2016) (USB Flash Drive), 10 Pages, 2016/10
The authors proposed and ECP evaluation model introducing irradiation-induced diffusion in the oxide layer to simulate neutron irradiation effect, and predicted with this model that ECP is started to depress from the neutron flux of about ten to the fourteenth per square meter. As the JMTR has in-pile loops applicable to water chemistry experiments, degree of irradiation effect on ECP appears in the in-pile loop was estimated by the model. Under oxygen injected condition, ECP in a capsule becomes constant along the vertical direction due to the presence of high amount of oxygen and hydrogen peroxide in a capsule. However, if neutron irradiation depress ECP, ECP in a capsule along vertical direction wouldn't become constant, and the degree to the decrement is detectable by experiments.
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
Uchida, Shunsuke; Hanawa, Satoshi; Kysela, J.*; Lister, D. H.*
Power Plant Chemistry, 18(1), p.6 - 17, 2016/01
In order to establish reliable NPP operation, each plant requires its own unique optimal water chemistry control based on careful consideration of its system, materials and operational history. Electrochemistry is one of key issues that determine corrosion related problems, e.g., FAC. Based on the relationships among ECP, metal surface conditions and exposure time, a model to evaluate ECP and corrosion rate of steel was developed by coupling an electrochemical model and an oxide layer growth model. Major conclusions are as follows. (1) The effects of water chemistry improvement and mass transfer coefficients due to local flow velocity on FAC wall thinning rate and ECP could be evaluated with the proposed model. (2) The effects of HO and O concentrations on ECP were evaluated with the model. Exposure time dependent ECPs were also explained as the effects of oxide film growth on the specimens. (3) Decreases in ECP due to neutron exposure were explained by radiation-induced diffusion in the oxide layers.
Uchida, Shunsuke; Hanawa, Satoshi; Lister, D. H.*
Power Plant Chemistry, 17(6), p.328 - 339, 2015/12
In nuclear power plants, radiation makes the relationship between structural materials and water chemistry much more complex than that in fossil fueled power plants. It is difficult to maintain safer and more reliable plant operation by controlling water chemistry based on only a restricted number of measured data. It is often required to control water chemistry with suitable assistance from computer models, which can extrapolate measured water chemistry parameters to those at the required locations and predict future trends of the interactions between structural materials and water chemistry. In the paper, water chemistry control based on parameters determined with plant simulation models and major computational models to be applied for water chemistry control are discussed.
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.
Hanawa, Satoshi; Hata, Kuniki; Shibata, Akira; Chimi, Yasuhiro; Kasahara, Shigeki; Tsutsui, Nobuyuki*; Iwase, Akihiro*; Nishiyama, Yutaka
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10
no abstracts in English
Hanawa, Satoshi; Hata, Kuniki; Chimi, Yasuhiro; Nishiyama, Yutaka
Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2013 (USB Flash Drive), 7 Pages, 2013/10
Water chemistry experiments will be carried out by using an in-pile loop newly installed in the JMTR. Concentrations of chemical species of O, H and HO are measured at the inlet and the outlet of the irradiation field. Electrochemical corrosion potential (ECP) at the irradiation field is also monitored. These experimental data will be obtained under wide range of experimental conditions such as absorption dose rate, H or O concentration in the feeding water and water temperature. As a result of preliminary calculations, it became clear that the in-pile loop in the JMTR is capable for water chemistry experiment. Although the operation of the JMTR is being delayed because of the Tohoku district off the Pacific Ocean earthquake, construction of the loops and installation of the instrumentation for the loops have been carried out almost on schedule. The experiments will be started after JMTR restart.
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.
Hanawa, Satoshi; Nakamura, Takehiko; Uchida, Shunsuke; Kus, P.*; Vsolak, R.*; Kysela, J.*; Sakai, Masanori*
Nuclear Technology, 183(1), p.136 - 148, 2013/07
no abstracts in English