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Owada, Kenji*; Tsukada, Shinya*; Fukuda, Tatsuo; Tsutsui, Satoshi*; Baron, A. Q. R.*; Mizuki, Junichiro*; Owa, Hidehiro*; Yasuda, Naohiko*; Terauchi, Hikaru*
Physical Review B, 98(5), p.054106_1 - 054106_10, 2018/08
Times Cited Count:3 Percentile:15.56(Materials Science, Multidisciplinary)Shimizu, Daisuke*; Tsukada, Shinya*; Matsuura, Masato*; Sakamoto, Junya*; Kojima, Seiji*; Namikawa, Kazumichi*; Mizuki, Junichiro; Owada, Kenji
Physical Review B, 92(17), p.174121_1 - 174121_5, 2015/11
Times Cited Count:13 Percentile:50.04(Materials Science, Multidisciplinary)The phase diagram and the relationship between the crystal coherence length and electrical response of Pb[(MgNb)Ti]O (PMN-xPT) near the morphotropic phase boundary (MPB) have been precisely investigated using a single crystal with a Ti composition gradient by synchrotron X-ray diffraction and inelastic light scattering at room temperature. The crystal has two boundaries at Ti compositions of 29.0 mol% and 34.7 mol% which correspond to the phase boundaries between the monoclinic B (MB) and C (MC) phases and between the MC and tetragonal (T) phases, respectively. It is shown that there is a strong negative correlation between the electrical response and the crystal coherence length at the sub-m scale. The results are explained by the size effects of domains near the MPB.
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.
Nakano, Junichi; Kaji, Yoshiyuki; Yamamoto, Masahiro; Tsukada, Takashi
Journal of Nuclear Science and Technology, 51(7-8), p.977 - 986, 2014/07
Times Cited Count:4 Percentile:30.92(Nuclear Science & Technology)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.
Nakano, Junichi; Yamamoto, Masahiro; Tsukada, Takashi
Nihon 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
Times Cited Count:3 Percentile:23.92(Materials Science, Multidisciplinary)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
Times Cited Count:2 Percentile:18.63(Materials Science, Multidisciplinary)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.
Kaji, Yoshiyuki; Miwa, Yukio*; Shibata, Akira; Nakano, Junichi; Tsukada, Takashi; Takakura, Kenichi*; Nakata, Kiyotomo*
International Journal of Nuclear Energy Science and Engineering, 2(3), p.65 - 71, 2012/09
Crack growth rate (CGR) tests have been conducted with neutron irradiated compact tension (CT) specimens. The specimens were irradiated in the core region of the Japan Materials Testing Reactor (JMTR) in simulated BWR water environments at 288 C from 0.37 to 5.5510 n/m (E 1 MeV) (0.62 to 9.2 dpa). The CGRs of base metals in high electrochemical corrosion potential (ECP) condition with 10 stress intensity factor, K 30 MPam, increased with increasing neutron fluence until 2 dpa and the CGRs were almost the same from 2 to 10 dpa. We investigated the influence of microstructure on CGR by microstructure observation and local strain measurement around the precipitate. This paper will discuss the relationship between CGR and microstructure, radiation hardening, radiation induced segregation.
Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Kaji, Yoshiyuki; Yamamoto, Masahiro; Tsukada, Takashi
Proceedings of 2012 Nuclear Plant Chemistry Conference (NPC 2012) (CD-ROM), 9 Pages, 2012/09
It has been reported that the corrosion behavior of stainless steels in high temperature water with hydrogen peroxide (HO) was different from those with O. To evaluate the effect of HO on stress corrosion cracking (SCC), SCC growth tests were conducted in high temperature water injected with HO. In 100 ppb HO at 561 K, an intergranular SCC (IGSCC) was observed only small portion of area near the side grooves of the CT specimen. In 100 ppb HO at 453 K, however, IGSCC extended to the central region of the CT specimen. Effects of HO on SCC growth behavior appeared stronger at lower temperature due to a reduction of the thermal decomposition of HO. Moreover, outer oxide layer of oxide film formed on the crack of the CT specimen was examined to estimate environmental situations in the cracks and a thermal equilibrium calculation was performed.
Yamamoto, Masahiro; Kato, Chiaki; Sato, Tomonori; Nakano, Junichi; Ugachi, Hirokazu; Tsukada, Takashi; Kaji, Yoshiyuki; Tsujikawa, Shigeo*; Hattori, Shigeo*; Yoshii, Tsuguyasu*; et al.
JAEA-Review 2012-007, 404 Pages, 2012/03
There are many LWRs which have been operated for more than 20 years in Japan and it is expected that technique corresponding to aging plants are necessary established for safety operation in LWRs. A lot of troubles related to SCC are reported and many investigations are concerned with SCC mechanism and technical evaluation. In this paper, those research data were collected as possible widely and reviewed systematically. Current circumstances concerned with SCC in LWRs were reviewed specifically as follows: SCC incidents, SCC evaluation methods for crack initiation and propagation, the investigations concerned with SCC mechanism and monitoring technique for corrosive environment. Influences with reactor types (BWR, PWR), materials (stainless steels, Ni alloys) and SCC evaluating methods (laboratories and actual plants) were summarized as graphs and tables easy to understand in common/difference points concerned with SCC. From these arranged results, future themes were considered and remarked SCC phenomenon was summarized in actual plants. As for SCC evaluations under the accelerate conditions in the laboratory test, it was suggested that a computational prediction and modeling including statistical technique and microscopic analysis in crack initiation were important. Furthermore it was suggested that monitoring techniques predicting SCC initiation and grasping plant circumstance in operation and feasibility in actual plants were important.
Shibata, Akira; Nakano, Junichi; Omi, Masao; Kawamata, Kazuo; Nakagawa, Tetsuya; Tsukada, Takashi
Journal of Nuclear Materials, 422(1-3), p.14 - 19, 2012/03
Times Cited Count:0 Percentile:0.01(Materials Science, Multidisciplinary)To simulate Irradiation assisted stress corrosion cracking (IASCC) behavior by in-pile experiments, it is necessary to irradiate specimens up to a neutron fluence that is higher than the IASCC threshold fluence. Pre-irradiated specimens must be relocated from pre-irradiation capsules to in-pile capsules. Hence, a remote welding machine has been developed. And the integrity of capsule housing for a long term irradiation was evaluated by tensile tests in air and slow strain rate tests in water. Two type specimens were prepared. Specimens were obtained from the outer tubes of capsule irradiated to 1.0-3.9 10 n/m (E 1 MeV). And specimens were irradiated in a leaky capsule to 0.03-1.0 10 n/m. Elongation more than 15% in tensile test at 423 K was confirmed and no IGSCC fraction was shown in SSRT at 423 K which was estimated as temperature at the outer tubes of the capsule under irradiation.
Nakano, Junichi; Nemoto, Yoshiyuki; Tsukada, Takashi; Uchimoto, Tetsuya*
Journal of Nuclear Materials, 417(1-3), p.883 - 886, 2011/10
Times Cited Count:2 Percentile:18.29(Materials Science, Multidisciplinary)To examine the effects of minor elements on stress corrosion cracking (SCC) susceptibility of low carbon stainless steels with work hardened layer, a high purity type 304 stainless steel was fabricated and minor elements, Si, S, P, C or Ti, were added. Work hardened layer was introduced by shaving on the surface of stainless steels. The specimens were exposed to a boiling 42% MgCl solution for 20 hours and the number and the length of initiated cracks were examined. SCC susceptibility of the specimen with P was the highest and that of the specimen with C was the lowest in all specimens. By magnetic force microscope examination, magnetic phase expected to be martensitic phase was detected near surface. Since corrosion resistance of martensite is lower than that of austenite, the minor elements additions would affect SCC susceptibility through the amount of the transformed martensite, i.e. austenite stability.
Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi
Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 7 Pages, 2011/10
To evaluate the effects of hydrogen peroxide (HO) on stress corrosion cracking (SCC) behavior of stainless steels (SSs), crack growth tests and in-situ electrochemical impedance spectroscopy (EIS) in high temperature water injected with HO were carried out. On the fracture surface of a compact tension (CT) specimen exposed 100 ppb HO at 561 K, intergranular SCC (IGSCC) was observed only near side grooves of the CT specimen. To increase the amount of remaining HO, Chevron notches were eliminated from a CT specimen. Consequently expansion of IGSCC area was observed into the central region of the CT specimen. EIS was conducted on SS creviced corrosion specimens. Using the obtained charge transfer resistance, ratio of remaining HO inside crevice was calculated with a differential equation code. Ratio of remaining HO in the CT specimen without Chevron notches was calculated as higher than that of the one with Chevron notches.
Kaji, Yoshiyuki; Kondo, Keietsu; Aoyagi, Yoshiteru; Kato, Yoshiaki; Taguchi, Taketoshi; Takada, Fumiki; Nakano, Junichi; Ugachi, Hirokazu; Tsukada, Takashi; Takakura, Kenichi*; et al.
Proceedings of 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors (CD-ROM), p.1203 - 1216, 2011/08
In order to investigate the effect of neutron dose rate on tensile property and irradiation assisted stress corrosion cracking (IASCC) growth behavior, the crack growth rate (CGR) test, tensile test and microstructure observation have been conducted with type 304 stainless steel specimens. The specimens were irradiated in high temperature water simulating the temperature of boiling water reactor (BWR) up to about 1dpa with two different dose rates at the Japan Materials Testing Reactor (JMTR). The radiation hardening increased with the dose rate, but there was little effect on CGR. Increase of the yield strength of specimens irradiated with the low dose rate condition was caused by the increase of number density of frank loops. Little difference of radiation-induced segregation at grain boundaries was observed in specimens irradiated by different dose rates. Furthermore, there was little effect on local plastic deformation behavior near crack tip in the crystal plasticity simulation.
Sato, Tomonori; Noda, Kazuhiko*; Kato, Chiaki; Yamamoto, Masahiro; Nakano, Junichi; Tsukada, Takashi
Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2009 (CD-ROM), p.232 - 237, 2009/10
In this work, to clarify the electrochemical behaviors at the surfaces of stainless steels (SSs) in high temperature water containing hydrogen peroxide (HO), the in-situ electrochemical impedance spectroscopy (EIS) of SSs exposed to high temperature water was carried out. The materials of test specimens were type 316L SS and type 304L SS. The range of the applied frequency in EIS was 100 kHz to 1 m or 10 mHz. The charge transfer resistance at the boundary between the oxide film and the base metal (R) in oxygen (O) condition was larger than R in HO condition. This indicates that the corrosion rate of type 316L SS in high temperature water containing HO is larger than that in O contained water. The R of type 316L SS was larger than that of type 304L SS in high temperature water containing HO. This indicates that the corrosion resistance of type 316L SS is higher than that of type 304L SS.
Kaji, Yoshiyuki; Miwa, Yukio; Shibata, Akira; Nakano, Junichi; Tsukada, Takashi; Takakura, Kenichi*; Nakata, Kiyotomo*
Proceedings of 14th International Conference on Environmental degradation of Materials in Nuclear Power Systems (CD-ROM), p.1181 - 1191, 2009/08
The CGR tests of neutron irradiated Type 304 SS were conducted in BWR conditions and the results were compared with those of Type 304L and 316L SS, and following results were obtained. (1) The CGR increase with increasing neutron fluence and the power law of K on the CGR was observed above F2 neutron fluence level (1.4 dpa). The different tendency is observed between Type 304 SS and L-grade SS (Type 304L and 316L SS) with increasing neutron fluence above F3 (4.3 dpa) level. (2) The CGR of Type 304 SS is slightly small as compared with those of Type 304L and 316L SS at the same neutron fluence and shows an increasing tendency above 4 dpa and reaches to 1.010m/s in 9 dpa. (3) The neutron fluence dependence on uniform elongation is different with Type 304, 304L SS and Type 316L SS, that is, the neutron fluence in which the local deformation like channeling deformation is dominant, is high for Type 316L SS.
Takaya, Shigeru; Nagae, Yuji; Yoshitake, Tsunemitsu; Nemoto, Yoshiyuki; Nakano, Junichi; Ueno, Fumiyoshi; Aoto, Kazumi; Tsukada, Takashi
E-Journal of Advanced Maintenance (Internet), 1(1), p.44 - 51, 2009/05
As the result of comparing the magnetic flux density and the IASCC susceptibility evaluated by SSRT test on neutron irradiated model alloys, it was shown that there is the relation without depending on dose level and chemical compositions as long as the contribution of neutron irradiation to SCC was seen. Furthermore, measuring the magnetic flux density of unirradiated simulated degraded materials indicates that not only change in chemical compositions but also some defects are needed for the magnetic flux density to increase. These results show the possibility of non-destructive estimation of susceptibility to IASCC by measuring magnetic flux density.
Izumo, Hironobu; Chimi, Yasuhiro; Ishida, Takuya; Kawamata, Kazuo; Inoue, Shuichi; Ide, Hiroshi; Saito, Takashi; Ise, Hideo; Miwa, Yukio; Ugachi, Hirokazu; et al.
JAEA-Technology 2009-011, 31 Pages, 2009/04
Regarding Irradiation Assisted Stress Corrosion Cracking (IASCC) for austenitic stainless steel of the light water reactor (LWR), a lot of data that concerns the post irradiation evaluation (PIE) is acquired. However, IASCC occurs in LWR condition. Therefore, it is necessary to confirm adequacy of the PIE data comparing the experiment data under the simulated LWR condition. Bigger specimen is needed to acquire the effective data for the destruction dynamics in the study of stress corrosion cracking under neutron irradiation condition. Therefore, development of a new crack growth unit which can load to bigger is necessary to the neutron irradiation test. As a result, a prospect was provided in the unit that could load to specimen by changing load mechanism to the lever type from the linear type. And also, in the development of crack propagation unit, some technical issues were extracted from the discussion of the unit structure adopting the LVDT (Linear Variable Differential Transformer).
Nakano, Junichi; Nemoto, Yoshiyuki; Miwa, Yukio; Usami, Koji; Tsukada, Takashi; Hide, Koichiro*
Journal of Nuclear Materials, 386-388, p.281 - 285, 2009/04
Times Cited Count:4 Percentile:30.49(Materials Science, Multidisciplinary)Crack initiation and crack growth processes of irradiation assisted stress corrosion cracking on stainless steels were studied by slow strain rate testing in oxygenated high temperature water at 561 K. In-situ observation was carried out during SSRT. Specimens of type 304 stainless steel were subjected to a solution annealing (SA), a thermally sensitization (TS), or a cold working (CW) and irradiated to 1.010 n/m (E 1 MeV) at 323 K in the Japan Material Testing Reactor (JMTR). Crack initiations were observed before the maximum stress would be reached for the CW material in in-situ observation. In fracture surface examination, the TS material exhibited almost intergranular stress corrosion cracking while mixtures of transgranular stress corrosion cracking and ductile dimple fracture were observed for the SA and the CW materials.
Ishii, Tetsuro; Makii, Hiroyuki*; Asai, Masato; Tsukada, Kazuaki; Toyoshima, Atsushi; Matsuda, Makoto; Makishima, Akiyasu*; Shigematsu, Soichiro*; Kaneko, Junichi*; Shizuma, Toshiyuki; et al.
Physical Review C, 78(5), p.054309_1 - 054309_11, 2008/11
Times Cited Count:14 Percentile:64.91(Physics, Nuclear)