Stability of ' precipitates in nickel based oxide dispersion-strengthened superalloys under high-temperature and heavy irradiation conditions

Konno, Azusa; Ono, Naoko*; Ukai, Shigeharu*; Kondo, Sosuke*; Hashitomi, Okinobu*; Kimura, Akihiko*

Materials Transactions, 60(11), p.2260 - 2266, 2019/11

https://doi.org/10.2320/matertrans.M2019050

A stability of cuboidal ' phase under heavy irradiation was studied for newly developed Ni-based Oxide Dispersion Strengthened (ODS) superalloy as a candidate for the core structural materials in VHTR or GFR. The ion irradiation was applied at 873K, 1073K, 1273K and the dose was 100 dpa. The ' phase remained the cuboidal shape at 873K but got out of the shape at 1073K after irradiation. Those growths can be explained by the Nelson-Hudson-Mazey (NHM) model. For the result of 1273K irradiation, however, huge ' phase appeared in the whole irradiated area at the post irradiation-observation. This behavior is interpreted in terms of disordering of the ordered ' phase due to cascade collision, and thus increasing Gibbs free energy of the disordered phase induces a change of the element distribution inside the irradiated area. The ordered ' phase was reproduced from the disordered state at the cooling after ion irradiation.

Ion irradiation effects on FeCrAl-ODS ferritic steel

Kondo, Keietsu; Aoki, So; Yamashita, Shinichiro; Ukai, Shigeharu*; Sakamoto, Kan*; Hirai, Mutsumi*; Kimura, Akihiko*

Nuclear Materials and Energy (Internet), 15, p.13 - 16, 2018/05

https://doi.org/10.1016/j.nme.2018.05.022

Radiation hardening and microstructural evolution of ion irradiated 12Cr-6Al ODS ferritic steel was studied. Ion irradiation experiments were performed using Fe ions up to the nominal displacement damage of 20 dpa at the irradiation temperature was 300C. The monotonical increase of radiation hardening with dose was confirmed by experimentally obtained hardness data. The radiation hardening was also calculated theoretically by introducing the microstructural character examined by TEM into the dispersed barrier hardening model. The results showed a good agreement with the experimentally obtained data up to 5 dpa, while a slight discrepancy was found between theoretical and experimental hardness values at 20 dpa. Radiation hardening was mainly caused by irradiation-induced defect clusters below the irradiation dose of 5 dpa. As the irradiation dose increased toward 20 dpa, an additional influence of the radiation appeared, which was assumed to be induced by ' phase transformation.

Welding technology R&D of Japanese accident tolerant fuel claddings of FeCrAl-ODS steel for BWRS

Kimura, Akihiko*; Yuzawa, Sho*; Sakamoto, Kan*; Hirai, Mutsumi*; Kusagaya, Kazuyuki*; Yamashita, Shinichiro

Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 10 Pages, 2017/09

http://www.wrfpm2017.org/upload/draft_file/F-059-PD1.pdf

The effect of Al addition on the PRW weldability of ODS steel is shown with the discussion focusing on the microstructure changes by the welding. The ordinary welding methods including electron beam (EB) welding and tungsten inert gas (TIG) welding were also applied to the SUS430 endcap welding to cladding tube made of FeCrAl-ODS steel. The endcap welded ODS steel tube samples were tensile tested at RT. The EB welded FeCrAl-ODS/SUS430 samples broke in the ODS steel tube, indicating that the weld bond is stronger than the ODS base metal. However, the TIG welded FeCrAl-ODS/SUS430 samples broke at a weld bond. X-ray CT scan analysis was performed for the weld bond, and the bonding strength was correlated with the X-ray CT results in order to assess the feasibility of those welding methods for ATF-ODS steel cladding.

Ultra-high temperature tensile properties of ODS steel claddings under severe accident conditions

Yano, Yasuhide; Tanno, Takashi; Oka, Hiroshi; Otsuka, Satoshi; Inoue, Toshihiko; Kato, Shoichi; Furukawa, Tomohiro; Uwaba, Tomoyuki; Kaito, Takeji; Ukai, Shigeharu*; et al.

Journal of Nuclear Materials, 487, p.229 - 237, 2017/04

https://doi.org/10.1016/j.jnucmat.2017.02.021

Ultra-high temperature ring tensile tests were carried out to investigate the tensile behavior of oxide dispersion strengthened (ODS) steel claddings and wrapper materials under severe accident conditions; temperatures ranged from room temperature to 1400C which is near the melting point of core materials. The experimental results showed that tensile strength of 9Cr-ODS steel claddings was highest in the core materials at the ultra-high temperatures between 900 and 1200C, but that there was significant degradation in tensile strength of 9Cr-ODS steel claddings above 1200C. This degradation was attributed to grain boundary sliding deformation with / transformation, which was associated with reduced ductility. On the other hand, tensile strength of recrystallized 12Cr-ODS and FeCrAl-ODS steel claddings retained its high value above 1200 C unlike the other tested materials. Present study includes the result of "R&D of ODS ferritic steel fuel cladding for maintaining fuel integrity at the high temperature accident condition" entrusted to Hokkaido University by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).

Overview on recent progress toward small specimen test technique

Wakai, Eiichi; Kikuchi, Takayuki; Kim, B.*; Kimura, Akihiko*; Nogami, Shuhei*; Hasegawa, Akira*; Nishimura, Arata*; Soldaini, M.*; Yamamoto, Michiyoshi*; Knaster, J.*

Fusion Engineering and Design, 98-99, p.2089 - 2093, 2015/10

https://doi.org/10.1016/j.fusengdes.2015.06.068

Application of master curve method to the evaluation of fracture toughness of F82H steels

Kim, B. J.; Kasada, Ryuta*; Kimura, Akihiko*; Wakai, Eiichi; Tanigawa, Hiroyasu

Journal of Nuclear Materials, 442(1-3), p.S38 - S42, 2013/11

https://doi.org/10.1016/j.jnucmat.2013.03.079

High temperature reaction tests between high-Cr ODS ferritic steels and U-Zr metallic fuel

Otsuka, Satoshi; Kaito, Takeji; Ukai, Shigeharu*; Inoue, Masaki; Okuda, Takanari*; Kimura, Akihiko*

Journal of Nuclear Materials, 441(1-3), p.286 - 292, 2013/10

https://doi.org/10.1016/j.jnucmat.2013.06.002

The Al addition to ODS ferritic steels considerably improves the compatibility between U-Zr fuel and the ODS steels. The threshold temperature for reaction layer formation is roughly 50K higher in the Al-containing ODS ferritic steels than in those same steels without Al addition. The activity calculation results obtained using general thermodynamic data indicate the possibility that stabilization of the intact alpha-Zr layer by Al addition is the main mechanism for the compatibility improvement by Al addition.

A Round robin program of master curve evaluation using miniature C(T) specimens; First round robin test on uniform specimens of reactor pressure vessel materials

Yamamoto, Masato*; Kimura, Akihiko*; Onizawa, Kunio; Yoshimoto, Kentaro*; Ogawa, Takuya*; Chiba, Atsushi*; Hirano, Takashi*; Sugihara, Takuji*; Sugiyama, Masanari*; Miura, Naoki*; et al.

Proceedings of 2012 ASME Pressure Vessels and Piping Conference (PVP 2012) (DVD-ROM), 7 Pages, 2012/07

Master curve (MC) approach for the fracture toughness evaluation is expected to be a powerful tool to assess the structural integrity of reactor pressure vessels (RPVs). In order to get sufficient number of reliable data for the MC approach from broken halves of surveillance test specimens for RPVs, the use of miniature specimens is necessary. For this purpose, a round robin test program on the miniature compact tension specimens (Mini-CT) of 4 mm thick for the MC approach of a Japanese RPV steel has been launched with the participation of academia, industries and a research institute in Japan. The program aims to verify the reliability of experimental data from Mini-CT, and to pick out further investigation items to be solved. As the first step of this program, four institutes carried out MC testing and evaluation using common test procedure and specimens. Valid reference temperature T was successfully obtained in each institute. However, the T values showed large differences with maximum of 34C. It was indicated on the reason of difference that there is a strong correlation between the T values and loading rate, which was selected by each institute per test standard.

Status of Japanese design and validation activities of test facilities in IFMIF/EVEDA

Wakai, Eiichi; Kikuchi, Takayuki; Kogawara, Takafumi; Kimura, Haruyuki; Yokomine, Takehiko*; Kimura, Akihiko*; Nogami, Shuhei*; Kurishita, Hiroaki*; Saito, Masahiro*; Nishimura, Arata*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 6 Pages, 2011/03

Japanese activities of test facilities in IFMIF-EVEDA (International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities) project have three subjects of engineering design of post irradiation examination (PIE) facilities, small specimen test technique (SSTT), and engineering design of high flux test module (HFTM), and this paper is summarized about present status. Functional analysis and design of 2-D and 3-D models of PIE facility were performed. In HFTM, as materials of heater, W-3Re alloy and/or SiC/SiC composite were selected in the points of high temperature materials, fabrication technology and some suitable properties such as resistance of thermal shock, high temperature re-crystallization, ductility, resistance of irradiation degradation, and low-activation. In SSTT, a test machine of fracture toughness was designed and developed for small specimens with 10 mm square, and it had high accuracy controllability for stress and displacement.

Effect of hydrogenation on the electronic state of metallic La hydrides probed by X-ray absorption sectroscopy at the La -edges

Ishimatsu, Naoki*; Sasada, Ryohei*; Maruyama, Hiroshi*; Ichikawa, Takayuki*; Miyaoka, Hiroki*; Kimura, Toru*; Tsubota, Masami*; Kojima, Yoshitsugu*; Tsumuraya, Takao*; Oguchi, Tamio*; et al.

Journal of Physics; Conference Series, 190, p.012070_1 - 012070_4, 2009/11

https://doi.org/10.1088/1742-6596/190/1/012070

We have investigated the effect of hydrogenation on La and electronic states in metallic LaH by X-ray absorption near edge structure at the La -edges. As the hydrogen content increases from 0 to 2.6, white-line intensity at the La -edges shows a remarkable increase in the range of 2.0. This is interpreted as the increase in La hole induced by interstitial H atoms on the octahedral sites. On the other hand, the shoulder structure at the La -edge disappears in the process of = 0.0 2.0, indicating that the - hybridization is weakened by H atoms on the tetrahedral sites. This study demonstrates that H atoms on the two interstitial H sites provide different contribution to the modification of the electronic states.