Analytical study on stress behavior of core graphite components using simplified viscoelastic evaluation model

Saijo, Tomoaki; Shimazaki, Yosuke; Ishihara, Masahiro

JAEA-Technology 2025-010, 126 Pages, 2025/12

JAEA-Technology-2025-010.pdf:12.52MB

During the operation of the High Temperature Engineering Test Reactor (HTTR), thermal stress is generated in the graphite components. In addition, graphite exhibits dimensional shrinkage and creep deformation under neutron irradiation. As a result, residual stress remains in the graphite components during reactor shutdown. Therefore, in the design of the HTTR core graphite structures, stress analyses of the graphite components have previously been performed using the finite element analysis code VIENUS. In the HTTR, the graphite components are exposed to a wide range of temperature, from approximately 400C to 1200C, depending on their location. Consequently, irradiation-induced behaviors such as material property changes and irradiation shrinkage vary among the graphite components. On the other hand, since VIENUS code evaluates stress based on thermal fluid and heat conduction analysis results, it is not suitable for parametric studies. In this study, the influence of irradiation behavior on the stress behavior of graphite components in the wide temperature range (400C to 1200C) was analyzed using simplified viscoelastic evaluation model, consisting of two beam elements, to conduct efficient parametric studies. Operational stress exhibits two distinct patterns depending on whether the irradiation temperature is below or above 800C, due to irradiation shrinkage. Residual stress approaches the thermal stress, preventing excessive increase even when irradiation shrinkage is large. Moreover good agreement in stress behavior trends was observed between the stress analysis results by the simplified viscoelastic evaluation model and VIENUS code. These results indicate that the simplified viscoelastic evaluation model is beneficial in simulating stress behavior.

Residual stresses of small-bore butt-welded piping measured by quantum beam hybrid method

Suzuki, Kenji*; Miura, Yasufumi*; Toyokawa, Hidenori*; Shiro, Ayumi*; Shobu, Takahisa; Morooka, Satoshi; Shibayama, Yuki

Quantum Beam Science (Internet), 9(2), p.15_1 - 15_15, 2025/06

https://doi.org/10.3390/qubs9020015

Effect of grain refinement on transgranular stress corrosion cracking in SUS304L under boiling water reactor conditions

Hirota, Noriaki; Nakano, Hiroko; Takeda, Ryoma; Ide, Hiroshi; Tsuchiya, Kunihiko; Kobayashi, Yoshinao*

Material Science and Technology of Japan, 61(6), p.248 - 252, 2024/12

A comparative analysis of the 0.2 % yield stress in SUS304L stainless steel revealed that lower strain rates and higher temperatures significantly reduce yield stress. Grain refinement from 68.6 m to 0.59 m minimally impacted the rate of yield stress reduction at slower strain rates. However, finer grains showed a decrease in yield stress at reactor operating temperature compared to room temperature. In slow strain rate tests under conditions promoting intragranular stress corrosion cracking (SCC), SUS304L with grain sizes of 28.4 m or smaller exhibited similar fracture strains comparable to those at reactor operating temperatures, whereas coarse-grained SUS304L showed reduced fracture strain. Microstructural analysis showed that in smaller grains, over 87 % of the fracture surface was ductile. In particular, SUS304L with 0.59 m grains exhibited a higher presence of {111} / 3 boundaries, which decreased with grain growth. These results indicate that grain refinement will suppress intragranular SCC by slowing corrosion progression through increased {111} / 3 boundaries.

Deformation behavior of individual constituent phases and components in multimodal magnesium alloys

Harjo, S.; Gong, W.; Aizawa, Kazuya; Yamasaki, Michiaki*; Kawasaki, Takuro

Nihon Zairyo Gakkai Dai-58-Kai X Sen Zairyo Kyodo Ni Kansuru Shimpojiumu Koen Rombunshu, p.58 - 60, 2024/07

Analyses of stress intensity factor solutions for subsurface flaws in flat plates

Li, S.; Li, Y.; Lu, K.*; Lacroix, V.*; Dulieu, P.*

Proceedings of the ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 18 Pages, 2024/07

https://doi.org/10.1115/PVP2024-122733

Quantitative analysis of microstructure evolution, stress partitioning and thermodynamics in the dynamic transformation of Fe-14Ni alloy

Li, L.*; Miyamoto, Goro*; Zhang, Y.*; Li, M.*; Morooka, Satoshi; Oikawa, Katsunari*; Tomota, Yo*; Furuhara, Tadashi*

Journal of Materials Science & Technology, 184, p.221 - 234, 2024/06

https://doi.org/10.1016/j.jmst.2023.10.037

Prediction of interfacial shear stress and pressure drop in vertical two-phase annular flow

Zhang, H.*; Umehara, Yutaro*; Yoshida, Hiroyuki; Mori, Shoji*

International Journal of Heat and Mass Transfer, 218, p.124750_1 - 124750_11, 2024/01

https://doi.org/10.1016/j.ijheatmasstransfer.2023.124750

Unstable stress-triaxiality development and contrasting weakening in two types of high-strength transformation-induced plasticity (TRIP) steels; Insights from a new compact tensile testing method

Matsuno, Takashi*; Fujita, Taiki*; Matsuda, Tomoko*; Shibayama, Yuki; Hojo, Tomohiko*; Watanabe, Ikumu*

Journal of Materials Processing Technology, 322, p.118174_1 - 118174_16, 2023/12

https://doi.org/10.1016/j.jmatprotec.2023.118174

The impact of high stress triaxiality on work hardening in transformation-induced plasticity (TRIP) steel has been widely acknowledged, particularly through measurements of the austenite fraction. Understanding this TRIP behavior is crucial for predicting material fracture in press-forming processes. However, the actual flow stresses under high-stress-triaxiality conditions remain largely undetermined. To address this gap, we developed a new tensile testing method using tiny notched round bars to investigate stress-triaxiality-induced work hardening in TRIP steels. The specimens were analyzed using two-dimensional micrometry to allow finite element analyses to identify the flow stress. Additionally, we conducted in situ tensile tests in which their crystal lattice stresses were monitored using synchrotron X-ray diffraction (XRD) to realize mechanism analyses of the unexpected work-hardening behavior identified by the developed tensile testing method. Our combined approach revealed a mutual, unstable increase in the flow stress and stress triaxiality in the TRIP-aided bainitic ferrite steel, which reduced the hardening exponent coefficients and thus induced a higher stress triaxiality. In contrast, the TRIP-aided martensitic steel exhibited a weakening behavior, characterized by a significant decrease in the hardening exponent coefficients in the case of the sharpest notch. XRD analyses showed that microstructural heterogeneity led to an extraordinarily high hydrostatic stress in the austenite phase, accounting for these contrasting behaviors. This finding challenges the established consensus on TRIP steels and suggests the need for a revised framework for their application in press-forming, taking into account stress-triaxiality conditions.

Measurement of mechanical behavior of B-enriched MgB wire using a pulsed neutron source

Machiya, Shutaro*; Osamura, Kozo*; Hishinuma, Yoshimitsu*; Taniguchi, Hiroyasu*; Harjo, S.; Kawasaki, Takuro

Quantum Beam Science (Internet), 7(4), p.34_1 - 34_17, 2023/10

https://doi.org/10.3390/qubs7040034

Deformation mechanism of a strong and ductile maraging steel investigated using X-ray synchrotron diffraction

Li, H.*; Liu, Y.*; Zhao, W.*; Liu, B.*; Tominaga, Aki; Shobu, Takahisa; Wei, D.*

International Journal of Plasticity, 165, p.103612_1 - 103612_20, 2023/06

https://doi.org/10.1016/j.ijplas.2023.103612

In order to clarify the strength properties of Co-free maraging steel, tensile experiment using high energy synchrotron X-ray diffraction was performed. Diffraction profiles from the martensitic and austenitic phases were obtained, and their strength and width were observed to vary as loading. Analysis of the diffraction profiles showed that the content of martensite in the as-aged material decreased slowly at low stress levels and decreased rapidly at high stress levels. On the other hand, the austenite phase in the as-solution materials was significantly transformed the martensite phase as the stress increased. It was clarified to be responsible for their respective strength properties.