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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

Defect analysis of matrix damage in reactor pressure vessel steel using WB-STEM

Yoshida, Kenta*; Toyama, Takeshi*; Inoue, Koji*; Nagai, Yasuyoshi*; Shimodaira, Masaki

Materia, 62(3), p.154 - 158, 2023/03

no abstracts in English

Journal Articles

Constraint effect on fracture behavior of underclad crack in reactor pressure vessel

Shimodaira, Masaki; Tobita, Toru; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi

Journal of Pressure Vessel Technology, 144(1), p.011304_1 - 011304_7, 2022/02

 Times Cited Count:0 Percentile:0(Engineering, Mechanical)

In the structural integrity assessment of a reactor pressure vessel (RPV), the fracture toughness (K$$_{Jc}$$) should be higher than the stress intensity factor at the crack tip of an under-clad crack (UCC), which is prescribed in JEAC4206-2016. However, differences in crack depth and existence of cladding between the postulated crack and fracture toughness test specimens would be affected to the plastic constraint state and K$$_{Jc}$$ evaluation. In this study, we performed fracture toughness tests and finite element analyses (FEAs) to investigate the effect of cladding on K$$_{Jc}$$ evaluation. FEA showed that the cladding decreased the plastic constraint in the UCC rather than the surface crack. Moreover, it was also found that the apparent K$$_{Jc}$$ for the UCC was higher than that for the surface crack from tests and the local approach.

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

Effect of plastic constraint and cladding on semi-elliptical shaped crack in fracture toughness evaluation for a reactor pressure vessel steel

Shimodaira, Masaki; Tobita, Toru; Nagoshi, Yasuto*; Lu, K.; Katsuyama, Jinya

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 8 Pages, 2021/07

In the structural integrity assessment of a reactor pressure vessel (RPV), the fracture toughness (K$$_{Jc}$$) should be higher than the stress intensity factor at the crack tip of a semi-elliptical shaped under-clad crack (UCC), which is prescribed in JEAC4206-2016. However, differences in crack depth and existence of cladding between the postulated crack and fracture toughness test specimens would be affected to the plastic constraint state and K$$_{Jc}$$ evaluation. In this study, we performed fracture toughness tests and finite element analyses to investigate the effect of plastic constraint and cladding on the semi-elliptical shaped crack in K$$_{Jc}$$ evaluation. The apparent K$$_{Jc}$$ value evaluated at the deepest point of the crack exceeded 5% fracture probability based on the Master Curve method estimated from C(T) specimens, and the conservativeness of the current integrity assessment method was confirmed. Few initiation sites were observed along the tip of semi-elliptical shaped crack other than the deepest point. The plastic constraint state was also analyzed along the crack tip, and it was found that the plastic constraint at the crack tip near the surface was lower than that for the deepest point. Moreover, it was quantitatively showed that the UCC decreased the plastic constraint. The local approach suggested higher K$$_{Jc}$$ value for the UCC than that for the surface crack, reflecting the low constraint effect for the UCC.

Journal Articles

Constraint effect on fracture mechanics evaluation for an under-clad crack in a reactor pressure vessel steel

Shimodaira, Masaki; Tobita, Toru; Takamizawa, Hisashi; Katsuyama, Jinya; Hanawa, Satoshi

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

In JEAC 4206 which prescribes the methodology for assessing the structural integrity of reactor pressure vessels (RPVs), an under-clad crack (UCC) at the inner surface of RPV is postulated, and it is required that the fracture toughness of RPV steels is higher than stress intensity factor for at the crack tip during the pressurized thermal shock event. In the present study, to investigate the effect of cladding on the fracture toughness, we performed three-point bending fracture toughness tests and finite element analyses (FEAs) for an RPV steel containing an UCC or a surface crack, and the constraint effect for UCC was also discussed. As the result, we found that the fracture toughness for UCC was considerably higher than that for surface crack. On the other hand, the FEAs showed that the cladding decreased the constraint effect for UCC.

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

Oral presentation

Microstructure analysis of ion-irradiated reactor pressure vessel steel using X-ray absorption

Iwata, Keiko; Ha, Yoosung; Takamizawa, Hisashi; Shimodaira, Masaki; Honda, Mitsunori; Okamoto, Yoshihiro

no journal, , 

no abstracts in English

Oral presentation

Effect of initial properties on irradiation hardening in RPV steel

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

no journal, , 

no abstracts in English

Oral presentation

The Overview of research on Materials Evaluation Research Group and summary of experiments on fracture mechanics

Shimodaira, Masaki; Hata, Kuniki; Iwata, Keiko; Ha, Yoosung; Kasahara, Shigeki; Katsuyama, Jinya

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

Microstructural analysis on ion- and neutron-irradiated reactor pressure vessel steel using XAFS methods

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

no journal, , 

In this study, we performed that extended X-ray absorption fine structure (EXAFS) analysis for ion- and neutron-irradiated reactor pressure vessel (RPV) steel to investigate microstructural changes of solute atom clusters induced by irradiation. To verify changes of EXAFS spectra recognized in ion-irradiated samples, we constructed lattice structure models with defects induced by irradiation and calculated theoretical EXAFS spectra for these models. Comparison between measured spectra and EXAFS simulations suggests that tensile-type interstitials or vacancy defects could be located around Cu and Ni atoms. Although the improvement for decreasing of noise in measured spectra at Cu K-edge, we will indicate that microstructure around Cu atoms may change from bcc structure due to irradiation.

Oral presentation

Fracture toughness and microstructural changes of highly neutron irradiated RPV steel under stainless-overlay cladding

Ha, Yoosung; Shimodaira, Masaki; Takamizawa, Hisashi; Katsuyama, Jinya; Nagai, Yasuyoshi*

no journal, , 

no abstracts in English

Oral presentation

The Overview of research on Materials Evaluation Research Group and a study on the structural integrity assessment of reactor pressure vessels

Hata, Kuniki; Iwata, Keiko; Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Katsuyama, Jinya

no journal, , 

no abstracts in English

Oral presentation

Irradiation induced defects analysis in the heat affected zone of a reactor pressure vessel steel by transmission electron microscopy

Shimodaira, Masaki; Ha, Yoosung; Takamizawa, Hisashi; Seto, Hitoshi*; Katsuyama, Jinya

no journal, , 

no abstracts in English

Oral presentation

Fracture toughness distribution of a thick plate of A533B with welding

Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya

no journal, , 

In Japanese surveillance program for RPV, the specimens are taken from base metal of a quarter thickness in a plate, weld metal and heat affected zone (HAZ) as representative materials. JEAC4201 specifies Embrittlement Trend Curve (ETC) for base metal but not for HAZ, because the fracture toughness of HAZ is considered to be generally better than that of base metal. However, since the microstructures in HAZ are inhomogeneous due to multi-pass welding, it is necessary to investigate the fracture toughness of HAZ with more specific basis. The Charpy impact properties and fracture toughness (T$$_{41J}$$ and T$$_{o}$$) derived from three representative positions in HAZ were compared with those of base metal. T$$_{41J}$$ and T$$_{o}$$ of HAZ were lower than those of base metal, meanwhile the results of Charpy impact test and fracture toughness test for HAZ indicated a relatively large scatter.

Oral presentation

Evaluation of mechanical properties of weld heat-affected zone in reactor pressure vessel

Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya

no journal, , 

no abstracts in English

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