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Ukai, Shigeharu*; Ono, Naoko*; Otsuka, Satoshi
Comprehensive Nuclear Materials, 2nd Edition, Vol.3, p.255 - 292, 2020/08
Fe-Cr-based oxide dispersion strengthened (ODS) steels have a strong potential for high burnup (long-life) and high-temperature applications typical for SFR fuel cladding. Current progress in the development of Fe-Cr-based ODS steel claddings is reviewed, including their relevant mechanical properties, e.g. tensile and creep rupture strengths in the hoop directions. In addition, this paper reviewed the current research status on corrosion resistant Fe-Cr-Al-based ODS steel claddings, which are greatly paid attention recently as the accident tolerant fuel claddings for the light water reactor (LWR) and also as the claddings of the lead fast reactors (LFR) utilizing Pb-Bi eutectic (LBE) coolant.
Sakamoto, Naoki; Fujishima, Tadatsune; Mizukoshi, Yasutaka
Hozengaku, 19(2), p.125 - 126, 2020/07
The five post-irradiation examination facilities in JAEA's Oarai research and development institute have been operated for over 40 years in order to investigate the irradiation performance of fast reactor fuel materials. The equipment associated with these facilities has been managed to maintain secure from the problems occurred in the process of aging. Therefore, we established a safety assessment method for aging facilities in 2002, and we have been conducting maintenance management of facilities since then. In this study, improvement plans of the safety assessment method are considered in order to solve the issues detected as a result of analysis of past maintenance information.
Sekio, Yoshihiro; Sakaguchi, Norihito*
Materials Transactions, 60(5), p.678 - 687, 2019/05
The quantitative evaluation of vacancy migration energies in high nickel model alloy was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe-15Cr-xNi (x=15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K and electron irradiated at 576 K-824 K were examined. The VDZ widths increased with increasing Ni content in both irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. From the obtained energies, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.
Yano, Yasuhide; Sekio, Yoshihiro; Tanno, Takashi; Kato, Shoichi; Inoue, Toshihiko; Oka, Hiroshi; Otsuka, Satoshi; Furukawa, Tomohiro; Uwaba, Tomoyuki; Kaito, Takeji; et al.
Journal of Nuclear Materials, 516, p.347 - 353, 2019/04
Times Cited Count：1 Percentile：58.8(Materials Science, Multidisciplinary)9Cr-ODS steel claddings consisting of tempered martensitic matrix, showed prominent creep rupture strength at 1000 
C, which surpassed that of heat-resistant austenitic steels although creep rupture strength of tempered martensitic steels is generally lower than that of austenitic steels at high temperatures. The measured creep rupture strength of 9Cr-ODS steel claddings at 1000 C was higher than that from extrapolated creep rupture trend curves formulated using data at temperatures from 650 to 850 C. This superior strength seemed to be owing to transformation of the matrix from the 
-phase to the 
-phase. The transient burst strengths for 9Cr-ODS steel were much higher than those for 11Cr-ferritic/martensitic steel (PNC-FMS). Cumulative damage fraction analyses suggested that the life fraction rule can be used for the rupture life prediction of 9Cr-ODS steel and PNC-FMS claddings in the transient and accidental events with a certain accuracy.
Inoue, Toshihiko; Sekio, Yoshihiro; Watanabe, Hideo*
Materia, 58(2), P. 92, 2019/02
For the evaluation of irradiated segregation behavior, Austenite-based stainless steel for the fast reactor, during irradiation was evaluated by utilizing TIARA facility (Irradiate temperature: 600 C, Dose: 100 dpa) was observed by analytical electron microscope (JEM-ARM20FC). As a result of observation, the large-size void is observed in irradiation area, and MX segregation (containing Niobium) is not observed. In un-irradiation area the MX segregation is observed. And it is observed conspicuously that Nickel is segregation on the void surface. By the latest high-performance TEM utilization, these phenomenon are able to visualize. It is expected for the clarification of the irradiation damage and mechanism of void swelling, by the analyzing these phenomenon utilization with the latest high-performance TEM utilization.
Sekio, Yoshihiro; Yamagata, Ichiro; Akasaka, Naoaki; Sakaguchi, Norihito*
Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Next Generation Nuclear Systems for Sustainable Development (FR-17) (USB Flash Drive), 8 Pages, 2017/06
The widths of void denuded zones (VDZs) which were formed near random grain boundaries by neutron irradiation were analyzed in order to perform quantitative evaluations for the irradiation-induced point defect behavior in the modified 316 stainless steel (PNC316) having been developed by JAEA. Namely, the temperature dependence of VDZ width was investigated and vacancy migration energy of the PNC316 steel was estimated from the VDZ width analysis for the neutron-irradiated specimens. The obtained value of vacancy migration energy was estimated as 1.46 eV, which was consistent with that from the exiting method using electron in-situ examination. This indicates that VDZ analysis could be effective method to evaluate especially vacancy migration energy during irradiation, and this would be realized from not in-situ observation but post-irradiation examination in the case of neutron irradiation.
Kawashima, Koichiro*; Yano, Yasuhide; Tanno, Takashi; Kaito, Takeji
Dai-24-Kai Choompa Ni Yoru Hihakai Hyoka Shimpojiumu Koen Rombunshu (USB Flash Drive), p.99 - 104, 2017/01
no abstracts in English
Shizukawa, Yuta; Sekio, Yoshihiro; Sato, Isamu*; Maeda, Koji
Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 5 Pages, 2017/00
Electrochemical corrosion behavior under salt water in a type 304L stainless steel used to a part of BWR core materials was investigated to evaluate the possibility of crevice corrosion occurrence for the fuel assemblies which experienced seawater exposure in Fukushima Daiichi Nuclear Power Plant (1F) accident. Especially, focusing on the upper end plug part having the 304L SS crevice structure, measurement of repassivation potential for crevice corrosion (
) were carried out using the crevice test pieces fabricated by 304L SS plates. From the results, was lower than the spontaneous potential (
) when the conditions of 2500 ppm chloride ion concentration at over 50 C or that of 2500 ppm at over 80 C, which are included in the SFP water quality conditions. Therefore, in the 304L SS parts of the 1F fuel assemblies that experienced seawater exposure, there is a possibility of crevice corrosion occurrence.
Oka, Hiroshi; Tanno, Takashi; Otsuka, Satoshi; Yano, Yasuhide; Uwaba, Tomoyuki; Kaito, Takeji; Onuma, Masato*
Nuclear Materials and Energy (Internet), 9, p.346 - 352, 2016/12
Times Cited Count：10 Percentile：18.31(Nuclear Science & Technology)Yano, Yasuhide; Tanno, Takashi; Sekio, Yoshihiro; Oka, Hiroshi; Otsuka, Satoshi; Uwaba, Tomoyuki; Kaito, Takeji
Nuclear Materials and Energy (Internet), 9, p.324 - 330, 2016/12
Times Cited Count：7 Percentile：31.55(Nuclear Science & Technology)Tanno, Takashi; Yano, Yasuhide; Oka, Hiroshi; Otsuka, Satoshi; Uwaba, Tomoyuki; Kaito, Takeji
Nuclear Materials and Energy (Internet), 9, p.353 - 359, 2016/12
Times Cited Count：4 Percentile：47.23(Nuclear Science & Technology)Materials for core components of fusion reactors and fast reactors, such as blankets and fuel cladding tubes, must be excellent in high temperature strength and irradiation resistance because they will be exposed to high heat flux and heavy neutron irradiation. Oxide dispersion strengthened (ODS) steels have been developing as the candidate material. Japan Atomic Energy Agency (JAEA) have been developing 9 and 11 Chromium (Cr) ODS steels for advanced fast reactor cladding tubes. The JAEA 11Cr-ODS steels were rolled in order to evaluate their anisotropy. Tensile tests and creep tests of them were carried out at 700 C in longitudinal and transverse orientation. The anisotropy of tensile strength was negligible, though that of creep strength was distinct. The observation results and chemical composition analysis suggested that the cause of the anisotropy in creep strength was prior powder boundary including Ti-rich precipitates.
Sato, Yutaka*; Kokawa, Hiroyuki*; Fujii, Hiromichi*; Yano, Yasuhide; Sekio, Yoshihiro
Metallurgical and Materials Transactions A, 46(12), p.5789 - 5800, 2015/12
Dissimilar friction stir welding (FSW) of an 11% Cr ferritic/martensitic stee (PNC-FMS) to 316-grade austenitic stainless steel was attempted with a view to its potential application to the wrapper tubes of next-generation fast reactors. The mechanical properties and microstructure of the resulting welds were systematically examined, which revealed that FSW produces a defect-free stir zone in which material intermixing is notably absent. That is, both steels are separately distributed along a zigzagging interface in the stir zone when PNC-FMS is placed on the retreating side, with the tool plunging at the butt line. This interface did not act as a fracture site during small-sized tensile testing of the stir zone. Furthermore, the microstructure of the stir zone was refined in both the PNC-FMS and 316 stainless steel sides, resulting in improved mechanical properties over the respective base material regions.
Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro*
Journal of Nuclear Materials, 458, p.355 - 360, 2015/03
Times Cited Count：10 Percentile：21.46(Materials Science, Multidisciplinary)Irradiation-induced void denuded zone (VDZ) formation near grain boundaries was studied to clarify the effects of minor alloying elements on vacancy diffusivity during irradiation in PNC316 steel. The test materials were Fe-15Cr-15Ni steel without additives and PNC316 stainless steel, which contains minor alloying elements. These steels were neutron-irradiated in the experimental fast reactor JOYO and electron-irradiation was also carried out using 1 MeV high voltage electron microscopy. VDZ formation was analyzed from the TEM microstructural observations after irradiation. VDZs were formed near random grain boundaries in both Fe-15Cr-15Ni and PNC316 steels. The VDZ widths in the PNC316 steel were narrower than those for the Fe-15Cr-15Ni steel for all neutron and electron irradiations. The VDZ width analysis implied that the vacancy diffusivity was reduced in PNC316 steel as a result of interaction of vacancies with minor alloying elements.
Ozu, Akira; Tachi, Yoshiaki; Arita, Yuji*
Reza Kenkyu, 42(12), p.913 - 917, 2014/12
Laser-induced breakdown spectroscopy (LIBS) analysis has been applied to the molten alloy production process, in which simulated metals (Zr, Cu, Sm, Ce) are used instead of nuclear metallic fuels contained minor actinide (MA), with the aim of in-situ monitoring the elementary composition of the surface of the molten alloy in a chamber and vapor particles generated from the surface of the molten alloy. The variation in the ratio of elementary composition of the surface of the molten alloy in the crucible was successfully observed depending on temperature of the crucible. The elementary composition of the vapor particles appeared in the molten alloy chamber was also measured. The practical experimental results show that LIBS technique is very useful for investigating the elementary composition in the process and understanding the behavior of molten alloy in the crucible.
Sekio, Yoshihiro; Yamagata, Ichiro; Yamashita, Shinichiro; Inoue, Masaki; Maeda, Koji
Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 10 Pages, 2014/10
In the Fukushima Dai-ichi Nuclear Power Plant accident, seawater was temporarily injected into the spent fuel pools since water cooling and feeding functions were lost. For fuel assemblies which experienced seawater immersion, surface corrosion due to seawater constituents and the resultant degradation of mechanical property are of concern. Therefore, in order to assess the integrity of fuel assemblies (especially cladding tubes), the effects of seawater immersion on corrosion behavior and mechanical properties for as-recieved and irradiated Zircaloy-2 cladding tubes were investigated in the present study. As a result, no obvious surface corrosion and no significant degradation in the tensile strength property were observed after both artificial and natural seawater immersion tests for both steels. This suggests that the effects of seawater immersions on corrosion behavior and mechanical property (especially tensile property) for Zircaloy-2 cladding tubes are probably negligible.
Fukushima Project Team, Oarai Research and Development Center; Fukushima Fuels and Materials Department, Oarai Research and Development Center
JAEA-Technology 2014-020, 52 Pages, 2014/07
JAEA-Technology-2014-020.pdf:21.21MB
In this study, a screening study on corrosion phenomena and a preliminary investigation for an evaluation method on long-term integrity of FAs experienced unusual corrosive environment were carried out in views of fundamental features of corrosion. The screening study have led to the following two features of FAs from the viewpoint of the integrity as important phenomena to be further investigated; "fission product confinement of cladding tube" and "structural integrity of FA". In terms of "fission product confinement of cladding tube", it was shown experimentally that influence of the exposure to an unusual corrosive environment was low. On the other hand, in terms of "structural integrity of FA", a concept of experimental methodology for predicting long-term corrosion behavior was preliminary studied for preferentially selected FA local parts composed of different metals.
Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro
Materials Transactions, 55(3), p.438 - 442, 2014/03
Times Cited Count：7 Percentile：53.33(Materials Science, Multidisciplinary)In order to perform the comparative evaluations for vacancy diffusivity and flux between a base alloy and modified alloys, the void denuded zones (VDZ) widths were measured from the TEM in-situ observation during electron irradiation in the SUS316L, SUS316L-V and SUS316L-Zr steels. As a result, VDZs with given widths were formed near GBs. Then, the VDZ widths were different depending on steels, and the width was narrower due to addition of minor alloying elements which strongly interact with vacancies. Furthermore, from the analyses of measured VDZ widths in the SUS316L and SUS316L-V steels, the changes of vacancy diffusivity, vacancy flux and excess vacancy concentration were estimated as 0.50, 0.71 and 1.41, respectively. The decreases of vacancy diffusivity and flux during electron irradiation would be due to the interaction of vacancies with added minor elements, while the enhancement of the excess vacancy concentration would be caused by trapping effects due to alloying elements.
Yamagata, Ichiro; Hayashi, Takehiro; Mashiko, Shinichi*; Sasaki, Shinji; Inoue, Masaki; Yamashita, Shinichiro; Maeda, Koji
JAEA-Testing 2013-004, 23 Pages, 2013/11
JAEA-Testing-2013-004.pdf:8.59MB
In the accident of the Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Co. accompanying the Great East Japan Earthquake, fuel assemblies kept in the spent fuel pool of reactor units 1-4, were exposed to the inconceivable environment such as falling and mixing of rubble, especially seawater were injected into unit 2-4. In order to evaluate the integrity of the fuel assemblies in spent fuel pools, and in the long-term storage after transported to the common storage pool, the immersion tests were performed using zircaloy-2 fuel cladding tubes irradiated in the advanced thermal reactor Fugen. The immersion liquid was prepared with doubling dilution of artificial seawater, which temperature was 80 C and immersion time was about 336 hours, as assuming the situation of the pool. The results indicated zircaloy-2 cladding tubes had no significant corrosion and no influence on mechanical property by immersion tests with artificial seawater conditions of this work.
Yano, Yasuhide; Otsuka, Satoshi; Yamashita, Shinichiro; Ogawa, Ryuichiro; Sekine, Manabu; Endo, Toshiaki; Yamagata, Ichiro; Sekio, Yoshihiro; Tanno, Takashi; Uwaba, Tomoyuki; et al.
JAEA-Research 2013-030, 57 Pages, 2013/11
JAEA-Research-2013-030.pdf:48.2MB
It is necessary to develop the fast reactor core materials, which can achieve high-burnup operation improving safety and economical performance. Ferritic steels are expected to be good candidate core materials to achieve this objective because of their excellent void swelling resistance. Therefore, oxide dispersion strengthened (ODS) ferritic steel and 11Cr-ferritic/martensitic steel (PNC-FMS) have been respectively developed for cladding and wrapper tube materials in Japan Atomic Energy Agency. In this study, the effects of fast neutron irradiation on mechanical properties and microstructure of 9Cr-and 12Cr-ODS steel claddings for fast reactor were investigated. Specimens were irradiated in the experimental fast reactor Joyo using the CMIR-6 at temperatures between 420 and 835C to fast neutron doses ranging from 16 to 33 dpa. The post-irradiation ring tensile tests were carried out at irradiation temperatures.
Yano, Yasuhide; Sato, Yutaka*; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Ogawa, Ryuichiro; Kokawa, Hiroyuki*
Journal of Nuclear Materials, 442(1-3), p.S524 - S528, 2013/09
Times Cited Count：10 Percentile：28.98(Materials Science, Multidisciplinary)Friction stir welding was applied to the wrapper tube materials, 11Cr-ferritic/martensitic steel, intended for fast reactors and defect-free welds were successfully produced. Then, the mechanical and microstructural properties of the friction stir welded steel were investigated. The hardness values of the stir zone were about 550 Hv, and they had hardly any dependence on the rotational speed, although they were much higher than that of the base material. However, tensile strengths and elongations of the stir zones were better at 298 K, compared to those of the base material. These excellent tensile properties were attributable to the fine grain formation during friction stir welding. A part of this study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.
