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Hata, Kuniki; Hanawa, Satoshi; Chimi, Yasuhiro; Uchida, Shunsuke; Lister, D. H.*
Journal of Nuclear Science and Technology, 60(8), p.867 - 880, 2023/08
Times Cited Count：2 Percentile：53.91(Nuclear Science & Technology)One of the major subjects for evaluating the corrosive conditions in the PWR primary coolant was to determine the optimal hydrogen concentration for mitigating PWSCC without any adverse effects on major structural materials. As suitable procedures for evaluating the corrosive conditions in PWR primary coolant, a couple of procedures, i.e., water radiolysis and ECP analyses, were proposed. The previous article showed the radiolysis calculation in the PWR primary coolant, which was followed by an ECP study here. The ECP analysis, a couple of a mixed potential model and an oxide layer growth model, was developed originally for BWR conditions, which was extended to PWR conditions with adding Li
(Na) and H effects on the anodic polarization curves. As a result of comparison of the calculated results with INCA in-pile-loop experiment data as well as other experimental data, it was confirmed that the ECPs calculated with the coupled analyses agreed with the measured within 
100mV discrepancies.
Hata, Kuniki; Uchida, Shunsuke; Hanawa, Satoshi; Chimi, Yasuhiro
Proceedings of International Symposium on Contribution of Materials Investigations and Operating Experience to LWRs' Safety, Performance and Reliability (Fontevraud 10) (Internet), 11 Pages, 2022/00
Hanawa, Satoshi; Hata, Kuniki; Chimi, Yasuhiro; Kasahara, Shigeki
Proceedings of 21st International Conference on Water Chemistry in Nuclear Reactor Systems (Internet), 12 Pages, 2019/09
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 290
C 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 Fe
O
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.
Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Takeda, Masatoshi*; et al.
Advanced Sustainable Systems (Internet), 2(11), p.1800067_1 - 1800067_8, 2018/11
Times Cited Count：7 Percentile：27.76(Green & Sustainable Science & Technology)Moro, Takuya*; Kim, J.*; Yamanaka, Satoru*; Murayama, Ichiro*; Kato, Takanori*; Nakayama, Tadachika*; Takeda, Masatoshi*; Yamada, Noboru*; Nishihata, Yasuo; Fukuda, Tatsuo; et al.
Journal of Alloys and Compounds, 768, p.22 - 27, 2018/11
Times Cited Count：17 Percentile：66.2(Chemistry, Physical)
and Br and its effect on corrosion of a low-alloy steelHata, 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, H
O, 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.
Kim, J.*; Yamanaka, Satoru*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Takeda, Masatoshi*; et al.
Ferroelectrics, 512(1), p.92 - 99, 2017/08
Times Cited Count：14 Percentile：56.08(Materials Science, Multidisciplinary)Yamanaka, Satoru*; Kim, J.*; Nakajima, Akira*; Kato, Takanori*; Kim, Y.*; Fukuda, Tatsuo; Yoshii, Kenji; Nishihata, Yasuo; Baba, Masaaki*; Yamada, Noboru*; et al.
Advanced Sustainable Systems (Internet), 1(3-4), p.1600020_1 - 1600020_6, 2017/04
no abstracts in English
Wu, H.-Y.*; Takahashi, Shigeo*; Miyamura, Hiroko; Ozahata, Satoshi*; Nakao, Akihiro*
Electronic Imaging, 2017(1), p.118 - 130, 2017/01
Extracting hierarchical structures from networks provides us with an effective means of visualizing them, especially when they contain complicated node connectivities such as those in traffic and distributed networks. This paper presents an algorithm for inferring such partial orders by optimizing the network hierarchies along flow paths that are given as input. We study several network examples to demonstrate the feasibility of the proposed approach including course dependency charts, railway networks, and P2P networks.
Wu, H.-Y.*; Takahashi, Shigeo*; Miyamura, Hiroko; Ozahata, Satoshi*; Nakao, Akihiro*
Journal of Imaging Science and Technology, 60(6), p.060407_1 - 060407_13, 2016/11
Times Cited Count：0 Percentile：0.02(Imaging Science & Photographic Technology)Extracting hierarchical structures from networks provides us with an effective means of visualizing them, especially when they contain complicated node connectivities such as those in traffic and distributed networks. This paper presents an algorithm for inferring such partial orders by optimizing the network hierarchies along flow paths that are given as input. We study several network examples to demonstrate the feasibility of the proposed approach including course dependency charts, railway networks, and P2P networks.
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
Times Cited Count：6 Percentile：49.29(Nuclear Science & Technology) radiolysis of sodium chloride solutions containing a small amount of bromide ionHata, Kuniki; Inoue, Hiroyuki*; Kojima, Takao*; Iwase, Akihiro*; Kasahara, Shigeki; Hanawa, Satoshi; Ueno, Fumiyoshi; Tsukada, Takashi
Nuclear Technology, 193(3), p.434 - 443, 2016/03
Times Cited Count：13 Percentile：77.16(Nuclear Science & Technology)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.
Miyamura, Hiroko; Hu, H.-Y.*; Yoshida, Masahiro*; Ozahata, Satoshi*; Nakao, Akihiro*; Takahashi, Shigeo*
Shingaku Giho, 112(463), p.577 - 582, 2013/03
This report presents a method for visualizing scale-free networks including Overlay networks as an typical example. Visualizing large-scale and complicated networks such as social networks has recently been very popular while conventional network visualization techniques cannot allow us to understand the topological structure of the scale-free networks. This is because the vertex degrees vary at an exponential rate in the scale-free network and thus special attention should be given when visualizing the network connectivity and analyzing the network traffic there. In this report, we employ the hierarchical representation of the scale-free network by referring to their vertex degrees and autonomous system relationships, so that we can clearly visualize the topological structure of the network in 3D space and retrieve the traffic paths over the network.
, CO
and Br in seawater; Model calculation of radiolysis of seawaterHata, Kuniki; Hanawa, Satoshi; Kasahara, Shigeki; Muroya, Yusa*; Katsumura, Yosuke*
Proceedings of 2012 Nuclear Plant Chemistry Conference (NPC 2012) (CD-ROM), 6 Pages, 2012/09
Fukushima Daiichi Power Plants experienced seawater injection as emergent measure for a short period after the accident. As a result of seawater injection, structural materials in the reactors are exposed to unexpected corrosion environment due to Cl as well as radiolytic products by -rays from fuels. In the present study, a model calculation on seawater radiolysis was carried out to estimate concentration of radiolytic products under -irradiation. Radiolytic products, H, O and HO, in seawater monotonically increased with dose. H production was especially distinguished, and its yield was 4.4 
10
mol J
. As similar result was obtained from the calculation of NaBr solution, the main species which increased these products in seawater was thought to be Br. On the other hand, Cl and HCO in seawater hardly affected the concentrations of these radiolytic products.
