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Journal Articles

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

 Times Cited Count:27 Percentile:97.79(Materials Science, Multidisciplinary)

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 1400$$^{circ}$$C 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 1200$$^{circ}$$C, but that there was significant degradation in tensile strength of 9Cr-ODS steel claddings above 1200$$^{circ}$$C. This degradation was attributed to grain boundary sliding deformation with $$gamma$$/$$delta$$ 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 $$^{circ}$$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).

Journal Articles

Evaluation on tolerance to failure of ODS ferritic steel claddings at the accident conditions of fast reactors

Uwaba, Tomoyuki; Yano, Yasuhide; Otsuka, Satoshi; Naganuma, Masayuki; Tanno, Takashi; Oka, Hiroshi; Kato, Shoichi; Kaito, Takeji; Ukai, Shigeharu*; Kimura, Akihiko*; et al.

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 7 Pages, 2017/04

Tolerance of fast rector fuel elements to failure in the typical accident conditions was evaluated for the oxide-dispersion-strengthened (ODS) ferritic steel claddings that are candidate of the cladding material for advanced fast reactors. The evaluation was based on the cladding creep damage, which was quantified by the cumulative damage fractions (CDFs). It was shown that the CDFs of the ODS ferritic steel cladding were substantially lower than the breach limit of 1.0 in the loss of flow and transient over power conditions until a passive reactor shutdown system operates.

Journal Articles

High-temperature strength characterization of advanced 9Cr-ODS ferritic steels

Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji; Sakasegawa, Hideo*; Chikada, Nobuyoshi*; Hayashi, Shigenari*; Onuki, Somei*

Materials Science & Engineering A, 510-511, p.115 - 120, 2009/06

 Times Cited Count:79 Percentile:95.88(Nanoscience & Nanotechnology)

Oxide dispersion strengthened (ODS) ferritic steels, which are the most promising candidate materials for advanced fast reactor fuel elements, have exceptional creep strength at 973 K. The superior creep property of 9Cr-ODS ferritic steels is ascribed to the formation of a nonequilibrium phase, designated as the residual ferrite. The yield strength of the residual ferrite itself has been determined to be as high as 1360 MPa at room temperature from nanoindentation measurements. The creep strength is enhanced by minimizing the number of packet boundaries induced by the martensitic phase transformation. The creep strain occurs by sliding at weaker regions such as at the grain boundaries and packet boundaries. It is found that 9Cr-ODS ferritic steels behave as fiber composite materials comprising the harder residual ferrite and the softer tempered martensite.

Journal Articles

Super ODS steels R&D for fuel cladding of next generation nuclear systems, 10; Cladding tube manufacturing and summary

Ukai, Shigeharu*; Onuki, Somei*; Hayashi, Shigenari*; Kaito, Takeji; Inoue, Masaki; Kimura, Akihiko*; Fujisawa, Toshiharu*; Okuda, Takanari*; Abe, Fujio*

Proceedings of 2009 International Congress on Advances in Nuclear Power Plants (ICAPP '09) (CD-ROM), p.9232_1 - 9232_7, 2009/05

The super ODS cladding were manufactured into 8.5 mm outer diameter and 0.5 mm thickness by using pilger.mill rolling and intermediate heat treatment. The final heat treatment was successfully conducted at 1150 $$^{circ}$$C for 1h to make perfectly recrystallized structure. The manufactured cladding exhibits a secondary recrystallized grains with {110} $$<$$100$$>$$ Goss orientation. As a summary of super ODS steels R&D, the ODS steel, 16Cr-4Al-2W-0.1Ti added with small amount of Hf or Zr, is the prime candidate of "Super ODS steels" which has high strength at elevated temperatures, high resistance to corrosion for SCW and LBE, and high resistance to irradiation.

Oral presentation

Resistance to tempering of 9Cr-ODS ferritic steel

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kono, Yutaka*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

The mechanistic study was carried out on high-temperature strength of 9Cr-ODS ferritic steel that has a duplex microstructure of tempered martensite and residual-alpha ferrite. Microstructure characterizations were performed by micro and nano-hardness tests and microstructure observations after normalizing and tempering. Resistance to tempering was shown to increase with volume fraction of residual-alpha ferrite. This result is consistent with creep rupture test result. Individual strength of tempered martensite and residual-alpha ferrite was estimated from nano-hardenss and inter-particle spacing. In the presentation, discussion will be performed on the mechanism of residual-alpha ferrite formation as well as the effect of residual-alpha ferrite on high-temperature strength improvement.

Oral presentation

Formation of ultrafine grains in 9Cr-ODS ferritic steels

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Onuki, Somei*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

The hardness measurement by nanoindentation and microstructure analysis by TEM revealed that the tempering softening resistance of 9Cr-ODS ferritic steels is owing to the formation of ultrafine grains in residual ferrite phase.

Oral presentation

Texture formation by cold-rolling and recrystallization in ODS ferritic steels

Numata, Hiroya*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

The $$alpha$$ fiber texture of {115}$$sim$${111}$$<$$110$$>$$ aligned to the rolling plane and rolling direction is formed in 12Cr-ODS ferritic steels. The recrystallization texture of {110}$$<$$001$$>$$ can be formed at 1100$$^{circ}$$C.

Oral presentation

Residual-alpha ferrite formation mechanism in 9Cr-ODS ferritic steel

Yamamoto, Masahiro*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kaito, Takeji; Otsuka, Satoshi

no journal, , 

JAEA has found out and proved that high-temperature strength of 9Cr-ODS steel is considerably improved by the formation of residual-alpha ferrite/martensite duplex microstructure. This study discussed the mechanism on residual-alpha ferrite formation using thermo-dynamic model.

Oral presentation

Recrystallization mechanism of 12Cr-ODS ferritic steel

Numata, Hiroya*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

This study discussed the recrystallization mechanism from cold-worked texture in 12Cr-ODS ferritic steel.

Oral presentation

The Correlation between ultra-fine crystal grain formation and mechanical strength of ODS ferritic steel

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

It may be possible that the high-temperature strength of 9Cr-ODS ferritic/martensitic steel is largely improved by the formation of ultra-fine residual-alpha phase. This study discussed the correlation between ultra-fine residual-alpha formation and mechanical strength in ODS ferritic steel.

Oral presentation

The Correlation between ultra-fine crystal grain formation and mechanical strength of ODS ferritic steel

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

It may be possible that high-temperature strength of 9Cr-ODS ferritic/martensitic steel is largely improved by the ultra-fine residual-alpha phase. This study discussed the correlation between the ultra-fine residual alpha phase formation and mechanical strength.

Oral presentation

Residual-alpha ferrite formation mechanism in 9Cr-ODS ferritic steel

Yamamoto, Masahiro*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kaito, Takeji; Otsuka, Satoshi

no journal, , 

It may be possible that the high-temperature creep strength of 9Cr-ODS ferritic steel is largely improved by ultra-fine residual-alpha ferrite formation. This study discussed the mechanism on residual-alpha ferrite formation using thermodynamic model.

Oral presentation

High-temperature strength mechanism of 9Cr-ODS ferritic steels with complex structure

Ukai, Shigeharu*; Chikada, Nobuyoshi*; Hayashi, Shigenari*; Onuki, Somei*; Kaito, Takeji; Otsuka, Satoshi

no journal, , 

The 9Cr-ODS ferritic steel for fast reactor fuel cladding tube has been developed by JAEA. This study discussed the mechanism of high-temperature strength improvement produced by feeritic/martensitic duplex structure.

Oral presentation

Correlation between ultra-fine grain formation and high-temperature strength of 9Cr-ODS ferritic steel

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

no abstracts in English

Oral presentation

Alpha to $$gamma$$ reverse phase transformation behavior of 9Cr-ODS ferritic steel

Yamamoto, Masahiro*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

no abstracts in English

Oral presentation

$$alpha$$ to $$gamma$$ reverse phase transfomation behavior in 9Cr-ODS ferritic steel

Yamamoto, Masahiro*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

no abstracts in English

Oral presentation

Recrystalyzation mechanism in 12CrODS ferritic steel

Numata, Hiroya*; Hayashi, Shigenari*; Ukai, Shigeharu*; Otsuka, Satoshi; Kaito, Takeji

no journal, , 

no abstracts in English

Oral presentation

Correlation between high-temperature strength and microstructure of 9Cr-ODS ferritic steel

Yamamoto, Masahiro*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kaito, Takeji; Otsuka, Satoshi; Osaki, Satoshi*; Azuma, Tsukasa*

no journal, , 

no abstracts in English

Oral presentation

High temperature grain boundary sliding in ODS ferritic steel

Sugino, Yoshito*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kaito, Takeji; Otsuka, Satoshi

no journal, , 

no abstracts in English

Oral presentation

Relationship between residual-$$alpha$$ ferrite formation and high temperature tensile strength in 9Cr-ODS ferritic steel

Miyata, Ryota*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kaito, Takeji; Otsuka, Satoshi

no journal, , 

no abstracts in English

39 (Records 1-20 displayed on this page)