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.

An Evaluation on Inelastic Thermal Neutron Scattering Cross-Section Data of Crystalline Graphite

Okita, Shoichiro; Abe, Yutaka*; Tasaki, Seiji*; Fukaya, Yuji

Radioisotopes, 73(3), p.233 - 240, 2024/11

https://doi.org/10.3769/radioisotopes.73.233

High temperature nanoindentation of (U,Ce)O compounds

Frazer, D.*; Saleh, T. A.*; Matsumoto, Taku; Hirooka, Shun; Kato, Masato; McClellan, K.*; White, J. T.*

Nuclear Engineering and Design, 423, p.113136_1 - 113136_7, 2024/07

https://doi.org/10.1016/j.nucengdes.2024.113136

Nanoindentation based techniques can be employed on minute volumes of material to measure mechanical properties, including Young's modulus, hardness, and creep stress exponents. In this study, (U,Ce)O solid solutions samples are used to develop elevated temperature nanoindentation and nanoindentation creep testing methods for use on mixed oxide fuels. Nanoindentation testing was performed on 3 separate (Ux-1,Cex)O compounds ranging from x equals 0.1 to 0.3 at up to 800 C: their Young's modulus, hardness, and creep stress exponents were evaluated. The Young's modulus decreases in the expected linear manner while the hardness decreases in the expected exponential manner. The nanoindentation creep experiments at 800 C give stress exponent values, n=4.7-6.9, that suggests dislocation motion as the deformation mechanism.

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

Kim, G.*; Cho, S.-M.*; Im, S.*; Suh, H.*; Morooka, Satoshi; Shobu, Takahisa; Kanematsu, Manabu*; Machida, Akihiko*; Bae, S.*

Construction and Building Materials, 411, p.134529_1 - 134529_18, 2024/01

https://doi.org/10.1016/j.conbuildmat.2023.134529

Influence of group IV element on basic mechanical properties of BCC medium-entropy alloys using machine-learning potentials

Lobzenko, I.; Tsuru, Tomohito; 2 of others*

Computational Materials Science, 219, p.112010_1 - 112010_9, 2023/02

https://doi.org/10.1016/j.commatsci.2023.112010

Effect of magnesium silicate hydrate (M-S-H) formation on the local atomic arrangements and mechanical properties of calcium silicate hydrate (C-S-H); In situ X-ray scattering study

Kim, G.*; Im, S.*; Jee, H.*; Suh, H.*; Cho, S.*; Kanematsu, Manabu*; Morooka, Satoshi; Koyama, Taku*; Nishio, Yuhei*; Machida, Akihiko*; et al.

Cement and Concrete Research, 159, p.106869_1 - 106869_17, 2022/09

https://doi.org/10.1016/j.cemconres.2022.106869

Revealing the ion dynamics in LiGePS by quasi-elastic neutron scattering measurements

Hori, Satoshi*; Kanno, Ryoji*; Kwon, O.*; Kato, Yuki*; Yamada, Takeshi*; Matsuura, Masato*; Yonemura, Masao*; Kamiyama, Takashi*; Shibata, Kaoru; Kawakita, Yukinobu

Journal of Physical Chemistry C, 126(22), p.9518 - 9527, 2022/06

https://doi.org/10.1021/acs.jpcc.2c01748

Relevance of hydrogen bonded associates to the transport properties and nanoscale dynamics of liquid and supercooled 2-propanol

Zhai, Y.*; Luo, P.*; Nagao, Michihiro*; Nakajima, Kenji; Kikuchi, Tatsuya*; Kawakita, Yukinobu; Kienzle, P. A.*; Z, Y.*; Faraone, A.*

Physical Chemistry Chemical Physics, 23(12), p.7220 - 7232, 2021/03

https://doi.org/10.1039/d0cp05481j

Segmental motions of proteins under non-native states evaluated using quasielastic neutron scattering

Fujiwara, Satoru*; Matsuo, Tatsuhito*; Sugimoto, Yasunobu*; Shibata, Kaoru

Journal of Physical Chemistry Letters (Internet), 10(23), p.7505 - 7509, 2019/12

https://doi.org/10.1021/acs.jpclett.9b03196

Characterization of the dynamics of disordered polypeptide chains is required to elucidate the behavior of intrinsically disordered proteins and proteins under non-native states related to the folding process. Here we develop a method using quasielastic neutron scattering, combined with small-angle X-ray scattering and dynamic light scattering, to evaluate segmental motions of proteins as well as diffusion of the entire molecules and local side-chain motions. We apply this method to RNase A under the unfolded and molten-globule (MG) states. The diffusion coefficients arising from the segmental motions are evaluated and found to be different between the unfolded and MG states. The values obtained here are consistent with those obtained using the fluorescence-based techniques. These results demonstrate not only feasibility of this method but also usefulness to characterize the behavior of proteins under various disordered states.

Proposal of laser-induced ultrasonic guided wave for corrosion detection of reinforced concrete structures in Fukushima Daiichi Nuclear Power Plant decommissioning site

Furusawa, Akinori; Takenaka, Yusuke; Nishimura, Akihiko

Applied Sciences (Internet), 9(17), p.3544_1 - 3544_12, 2019/09

https://doi.org/10.3390/app9173544

Remote-controlled, non-destructive testing is necessary to detect corrosion of the reinforced concrete structures at the Fukushima Daiichi Nuclear Power Plant (NPP) de-commissioning site. This work aims to demonstrate that laser-induced ultrasonic guided wave technology can be applied to achieve this task. Hence, accelerated electrolytic corrosion is performed on a reinforced concrete specimen fabricated by embedding a steel rod into mortar. Waveforms of the laser-induced ultrasonic guided wave on the rod are measured with a previously employed piezoelectric transducer (PZT) probe, for each fixed corrosion time. Based on the results of Fourier and wavelet transforms of the waveforms, issues concerning the detection and extent of rebar corrosion are discussed. It is exhibited that the changes in bonding strength due to corrosion are distinguishable in the frequency domain of the ultrasonic signal.