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Journal Articles

Fracture toughness evaluation of weld-HAZ in RPV steel using Mini-C(T) specimens

Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya

Transactions of 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 7 Pages, 2024/03

Heat-affected zone (HAZ) produced by butt-welding in reactor pressure vessel (RPV) steel is one of the representative materials for surveillance program. The fracture toughness values of HAZ may show a large uncertainty due to inhomogeneous metallurgical structures. Also, the inhomogeneous microstructure in HAZ may influence on the degree of uncertainty in the fracture toughness and the sensitivity to irradiation embrittlement. We investigated the fracture toughness in HAZ of unirradiated material with respect to its distance from the fusion line of welds, where the amount of mixed microstructures change due to the thermal history during the welding. Mini-C(T) specimens of HAZ were harvested from the crack position at 0.5 mm, 1 mm and 2 mm from the fusion line of welds. The uncertainty of fracture toughness in HAZ, from the fusion line at 0.5 mm in particular, was larger than those of base metal at a quarter thickness. From the results of fracture toughness evaluation considering the standard deviation, there was the difference of reference temperature, $$T$$$$_{0}$$ in each position of HAZ. $$T$$$$_{0}$$ in all positions of HAZ was significantly lower than that of base metal, which means the fracture toughness in HAZ was greater than that of base metal at a quarter thickness.

Journal Articles

Analysis of the effect of pre-crack curvature in Mini-C(T) specimen on fracture toughness evaluation

Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Onizawa, Kunio

Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 11 Pages, 2023/07

In the current structural integrity assessment of the reactor pressure vessel, the accurate reference temperature (T$$_{o}$$) based on the Master Curve method is necessary. The T$$_{o}$$ can be estimated by using the Mini-C(T) fracture toughness specimen in accordance with ASTM E1921 and JEAC4216, which prescribe the pre-crack straightness criteria. A requirement in ASTM E1921 has been revised in a decade to increase the accuracy and reasonability, and the applicable crack curvature has been varied by applied codes. The pre-crack curvature of the Mini-C(T) specimen might have an impact on the T$$_{o}$$ because of the variation of the plastic constraint. In this work, the effect of the crack curvature on the fracture toughness (K$$_{Jc}$$) evaluation using the Mini-C(T) specimen was quantitatively evaluated by using the finite element analysis (FEA) including the Weibull stress analysis, to discuss the difference in a requirement of the crack straightness in ASTM E1921 and JEAC4216. FEAs showed a possibility that the upper limit curvature would decrease the plastic constraint, and consequently obtain higher K$$_{Jc}$$ in the Mini-C(T) specimen. Furthermore, if the upper limit curvature according to the ASTM E1921-21 was allowed, the T$$_{o}$$ would be estimated as non-conservative based on the Weibull stress analysis. In contrast, the difference in (T$$_{o}$$) between the crack with upper limit curvature according to JEAC4216 and the ideal straight crack was not significant.

Journal Articles

Fracture toughness evaluation of the heat-affected zone under the weld overlay cladding in reactor pressure vessel steel

Ha, Yoosung; Tobita, Toru; Takamizawa, Hisashi; Katsuyama, Jinya

Journal of Pressure Vessel Technology, 145(2), p.021501_1 - 021501_9, 2023/04

 Times Cited Count:1 Percentile:63.29(Engineering, Mechanical)

Journal Articles

EXAFS studies for atomic structural change induced by ion irradiation of a reactor pressure vessel steel

Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Shimodaira, Masaki; Okamoto, Yoshihiro; Honda, Mitsunori; Katsuyama, Jinya; Nishiyama, Yutaka

Nuclear Instruments and Methods in Physics Research B, 511, p.143 - 152, 2022/01

 Times Cited Count:0 Percentile:34.54(Instruments & Instrumentation)

Journal Articles

Fracture toughness in postulated crack area of PTS evaluation in highly-neutron irradiated RPV steel

Ha, Yoosung; Shimodaira, Masaki; Takamizawa, Hisashi; Tobita, Toru; Katsuyama, Jinya; Nishiyama, Yutaka

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 6 Pages, 2021/07

Journal Articles

Assessment of residual stress for thick butt-welded plate of a reactor pressure vessel steel

Ha, Yoosung; Okano, Shigetaka*; Takamizawa, Hisashi; Katsuyama, Jinya; Mochizuki, Masahito*

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 6 Pages, 2021/07

Journal Articles

Ion-induced irradiation hardening of the weld heat-affected zone in low alloy steel

Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi; Nishiyama, Yutaka

Nuclear Instruments and Methods in Physics Research B, 461, p.276 - 282, 2019/12

 Times Cited Count:3 Percentile:33.05(Instruments & Instrumentation)

Journal Articles

Study on irradiation hardening mechanism of RPV steel; Experiments for irradiation temperature control

Ha, Yoosung; Shimodaira, Masaki; Tobita, Toru; Hanawa, Satoshi; Yamasaki, Shota*; Uno, Sadanori*

2018-Nendo Ryoshi Kagaku Gijutsu Kenkyu Kaihatsu Kiko Shisetu Kyoyo Jisshi Hokokusho (Internet), 3 Pages, 2019/09

no abstracts in English

Journal Articles

Susceptibility to neutron irradiation embrittlement of heat-affected zone of reactor pressure vessel steels

Takamizawa, Hisashi; Katsuyama, Jinya; Ha, Yoosung; Tobita, Toru; Nishiyama, Yutaka; Onizawa, Kunio

Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 8 Pages, 2019/07

no abstracts in English

Journal Articles

Applicability of miniature compact tension specimens for fracture toughness evaluation of highly neutron irradiated reactor pressure vessel steels

Ha, Yoosung; Tobita, Toru; Otsu, Takuyo; Takamizawa, Hisashi; Nishiyama, Yutaka

Journal of Pressure Vessel Technology, 140(5), p.051402_1 - 051402_6, 2018/10

 Times Cited Count:6 Percentile:33.34(Engineering, Mechanical)

Journal Articles

Fracture toughness evaluation of heat-affected zone under weld overlay cladding in reactor pressure vessel steel

Ha, Yoosung; Tobita, Toru; Takamizawa, Hisashi; Hanawa, Satoshi; Nishiyama, Yutaka

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 6 Pages, 2018/07

Journal Articles

Microstructure analysis using X-ray absorption on heat-affected zone of reactor pressure vessel steel

Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Okamoto, Yoshihiro; Shimoyama, Iwao; Honda, Mitsunori; Hanawa, Satoshi; Nishiyama, Yutaka

Photon Factory Activity Report 2017, 2 Pages, 2018/00

no abstracts in English

Journal Articles

Fracture toughness evaluation of neutron-irradiated reactor pressure vessel steel using miniature-C(T) specimens

Ha, Yoosung; Tobita, Toru; Takamizawa, Hisashi; Nishiyama, Yutaka

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 5 Pages, 2017/07

The applicability of miniature-C(T) (Mini-C(T)) specimens to fracture toughness evaluation was investigated for neutron-irradiated reactor pressure vessel (RPV) steel. $$T_{o}$$ value determined from irradiated Mini-C(T) specimens was in good agreement with that determined from the irradiated pre-cracked Charpy-type (PCCv) specimens. Also, the scatter of the 1T-equivalent fracture toughness values obtained from the irradiated Mini-C(T) specimens was not significantly different from that obtained from the irradiated PCCv. $$T_{o}$$ values determined from Mini-C(T) specimens agreed very well with the correlation between Charpy 41J transition temperature and $$T_{o}$$ of commercially manufactured RPV steels.

Oral presentation

Microstructure analysis on thermally aged stainless overlay cladding using X-ray absorption

Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Okamoto, Yoshihiro; Shimoyama, Iwao; Kojima, Hiroshi*; Mayumi, Ren*; Iwase, Akihiro*; Nagai, Yasuyoshi*; Nishiyama, Yutaka

no journal, , 

Microstructure analysis for thermally aged stainless overlay cladding was conducted by using X-ray absorption. X-ray absorption fine structure analysis was adapted, which was possible to obtain the average information of a material and to identify the bond length and chemical state by the selected atoms. In this study, changes of coordination number and bond length around the Mn atom were recognized.

Oral presentation

The Correlation between microstructure and ion irradiation hardening in heat affected zone of reactor pressure vessel

Ha, Yoosung; Takamizawa, Hisashi; Iwata, Keiko; Tobita, Toru; Chimi, Yasuhiro; Katsuyama, Jinya; Nishiyama, Yutaka

no journal, , 

The microstructure of heat affected zone (HAZ) in stainless over-ray clad is predicted by finite element method (FEM). From the results of FEM analysis, the coarse grain area and fine grain area could obtain from HAZ and base metal also obtained in 1/4 thickness part for the irradiation experiment. After ion irradiation, the irradiation hardening of HAZ has higher tendency than that of base metal. In addition, the change of hardening is observed in fine grain area.

Oral presentation

Microstructure and hardening of ion-irradiated heat-affected zone of reactor pressure vessel steel

Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Nishiyama, Yutaka; Yoshida, Kenta*; Toyama, Takeshi*; Nagai, Yasuyoshi*

no journal, , 

Heat-affected zone of stainless over-ray clad is included in a supposed cracking area during the pressurized thermals shock regime. It is necessary to confirm the irradiation embrittlement susceptibility of HAZ compared with that of matrix. In this study, Fe$$^{2+}$$ ion irradiated into HAZ and matrix. We discussed the correlation between irradiation hardening and microstructure in HAZ. The irradiation hardening of SCFGHAZ is highest. As results of TEM observation, the precipitates dispersed with ~200 nm of sizes in SCFGHAZ specimen. Also, dislocation loops with high density by irradiation exist.

Oral presentation

Ion irradiation-induced microstructural changes in heat-affected zone of stainless weld overlay cladding of RPV steel

Ha, Yoosung; Takamizawa, Hisashi; Hanawa, Satoshi; Nishiyama, Yutaka; Ebisawa, Naoki*; Toyama, Takeshi*; Nagai, Yasuyoshi*

no journal, , 

Heat affected zone (HAZ) under stainless overlay cladding of RPV steel was irradiated by iron ions. To investigate the mechanism of irradiation hardening, the solute clusters distributions were confirmed by 3D-Atom Probe Tomography analysis, and the correlation between the irradiation hardening and the microstructure change in HAZ and matrix was discussed. As result of APT analysis, Cu and Si-Mn-Ni clusters were observed in irradiated area, but not in un-irradiated area. The distributions of cluster were different in coarse grain HAZ, fine grain HAZ and matrix, and the amounts of clusters in matrix were significantly lower than that in HAZ. In addition, size, chemical composition and number densities of clusters and their distributions were correlated with irradiation hardening.

Oral presentation

Effect of ion irradiation on microstructural change and hardening in HAZ under weld overlay cladding of RPV

Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi; Nishiyama, Yutaka; Yoshida, Kenta*; Toyama, Takeshi*; Nagai, Yasuyoshi*

no journal, , 

This talk will present the effect of ion irradiation on heat affected zone (HAZ) of stainless overlay cladding in RPV steels. After ion-irradiation, microstructural changes of HAZ were observed by TEM and APT. We confirmed the distributions of precipitates and solute clusters in both HAZ and base metal. Correlation between irradiation hardening and microstructural changes will be discussed in this study.

Oral presentation

Ion irradiation effect on micro structures of heat affected zone under stainless overlay clad in RPV steel

Ha, Yoosung; Takamizawa, Hisashi; Hanawa, Satoshi; Nishiyama, Yutaka; Ebisawa, Naoki*; Yoshida, Kenta*; Toyama, Takeshi*; Nagai, Yasuyoshi*

no journal, , 

Stainless overlay clad is welded on the inner surface of the reactor pressure vessel steel to prevent corrosion by the primary coolant. Heat affected zone (HAZ) is created during the welding and the micro structure at the HAZ is different from that of the base metal. This microstructural difference would cause the difference in irradiation hardening as well as embrittlement between the HAZ and the base metal. In order to confirm the irradiation embrittlement susceptibility of HAZ, Fe2+ ion irradiation experiment was carried out to both the HAZ and the base metal in this study. As results of TEM observation, precipitates dispersed with the size of ~200 nm in SCFGHAZ. Also, finer and higher number density of solute clusters were observed in the HAZ than that of the base metal by the atom prove tomography analysis. It was considered that the higher irradiation hardening of HAZ was caused by the precipitates and these solute clusters.

Oral presentation

JAEA research on the structural integrity assessment of reactor pressure vessel for safe long-term operation; Fracture toughness evaluation

Ha, Yoosung; Takamizawa, Hisashi; Tobita, Toru; Nishiyama, Yutaka

no journal, , 

no abstracts in English

36 (Records 1-20 displayed on this page)