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

https://doi.org/10.1115/1.4051704

In the structural integrity assessment of a reactor pressure vessel (RPV), the fracture toughness (K) 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 evaluation. In this study, we performed fracture toughness tests and finite element analyses (FEAs) to investigate the effect of cladding on K 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 for the UCC was higher than that for the surface crack from tests and the local approach.

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

https://doi.org/10.1016/j.nimb.2019.10.018

Confirmation tests for Warm Pre-stress (WPS) effect in reactor pressure vessel steel (Contract research)

Chimi, Yasuhiro; Iwata, Keiko; Tobita, Toru; Otsu, Takuyo; Takamizawa, Hisashi; Yoshimoto, Kentaro*; Murakami, Takeshi*; Hanawa, Satoshi; Nishiyama, Yutaka

JAEA-Research 2017-018, 122 Pages, 2018/03

JAEA-Research-2017-018.pdf:44.03MB

Warm pre-stress (WPS) effect is a phenomenon that after applying a load at a high temperature fracture does not occur in unloading during cooling, and then the fracture toughness in reloading at a lower temperature increases effectively. Engineering evaluation models to predict an apparent fracture toughness in reloading are established using experimental data with linear elasticity. However, there is a lack of data on the WPS effect for the effects of specimen size and surface crack in elastic-plastic regime. In this study, fracture toughness tests were performed after applying load-temperature histories which simulate pressurized thermal shock transients to confirm the WPS effect. The experimental results of an apparent fracture toughness tend to be lower than the predictive results using the engineering evaluation models in the case of a high degree of plastic deformation in preloading. Considering the plastic component of preloading can refine the engineering evaluation models.

Spin model of O-based magnet in a nanoporous metal complex

Soda, Minoru*; Homma, Yuki*; Takamizawa, Satoshi*; Kawamura, Seiko; Nakajima, Kenji; Masuda, Takatsugu*

Journal of the Physical Society of Japan, 85(3), p.034717_1 - 034717_9, 2016/03

https://doi.org/10.7566/JPSJ.85.034717

Inelastic neutron scattering experiments are performed on the nanoporous metal complex Cu--1,4-cyclohexanedicarboxylic acid (Cu-CHD) adsorbing O molecules to identify the spin model of the O-based magnet realized in the host complex. It is found that the magnetic excitations of Cu-CHDs adsorbing low- and high-concentration O molecules are explained by different spin models, the former by spin dimers and the latter by spin trimers. By using the obtained parameters and by assuming that the levels of the group of the highest energy states are reduced because of the nonnegligible spin dependence of the molecular potential of oxygen, the magnetization curves are explained quantitatively.

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.

Microstructure analysis using X-ray absorption on HAZ of ion-irradiated RPV steel

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

no journal, , 

no abstracts in English

Solute cluster formation in heat-affected zone of ion-irradiated low alloy steel

Ha, Yoosung; Iwata, Keiko; Takamizawa, Hisashi; Hanawa, Satoshi; Nishiyama, Yutaka

no journal, , 

no abstracts in English

Ion-induced microstructural change of A533B steel analyzed by X-ray absorption fine structure spectroscopy

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

no journal, , 

no abstracts in English

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.

Microstructural change of heat-affected zone under stainless overlay cladding of RPV steel irradiated with ions

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

no journal, , 

no abstracts in English