Numerical verification for the effect of suppressing hydrogen embrittlement by Sn doping in the Al-Zn-Mg alloy

Ebihara, Kenichi; Fujihara, Hiro*; Shimizu, Kazuyuki*; Yamaguchi, Masatake; Toda, Hiroyuki*

International Journal of Hydrogen Energy, 136, p.751 - 756, 2025/06

https://doi.org/10.1016/j.ijhydene.2024.05.146

It has been experimentally reported that adding tin (Sn) to high-strength aluminum-zinc-magnesium (Al-Zn-Mg) alloys effectively suppresses hydrogen (H) embrittlement, which may be attributed to H absorption by the second-phase particles of Sn. To verify this fact, a simulation of H entry into the Sn phase in Al was performed using a model based on the reaction-diffusion equation that incorporates the solid solution energy of H evaluated by first-principles calculations. The results showed that the H solid solution site concentration of the second-phase particles must be at least five times higher than that of the Al phase for H absorption by the Sn second-phase particles to suppress H embrittlement. Therefore, the actual H embrittlement suppression effect of Sn second-phase particles is limited, and other factors may influence the suppression of H embrittlement in the experiment.

path-integral simulations of hydrogen-isotope diffusion in face-centred cubic metals

Kimizuka, Hajime*; Ogata, Shigenobu*; Thomsen, B.; Shiga, Motoyuki

Journal of Physics; Condensed Matter, 37(19), p.193001_1 - 193001_16, 2025/04

https://doi.org/10.1088/1361-648X/adc060

Calculations of hydrogen isotope diffusion coefficients for face-centred cubic lattice metals using path integral methods show that the temperature dependence of the diffusion coefficients has an unusual shape. This is due to the competition between nuclear quantum effects with different temperature dependence, which explains the unusual crossover mechanism between the normal and inverse isotope effects. We also present the results of a path integral simulation that describes approximate quantum dynamics using machine learning-based interatomic potentials with almost the same accuracy as density functional theory calculations. This computational method paves the way for understanding the quantum behaviour of hydrogen isotopes in various solid-state materials.

Transport and confinement physics Chapter 2 of the special issue: on the path to tokamak burning plasma operation

Yoshida, M.*; McDermott, R. M.*; Angioni, C.*; Camenen, Y.*; Citrin, J.*; Jakubowski, M.*; Hughes, J. W.*; Idomura, Yasuhiro; Mantica, P.*; Mariani, A.*; et al.

Nuclear Fusion, 65(3), p.033001_1 - 033001_132, 2025/02

https://doi.org/10.1088/1741-4326/ad8ced

Progress in physics understanding and theoretical model development of plasma transport and confinement in the ITPA Transport and Confinement Topical Group since the publication of the ITER Physics Basis was summarized focusing on the contributions to ITER and burning plasma prediction and control. This paper provides a general and streamlined overview on the advances that were mainly led by the ITPA TC joint experiments and joint activities for the last 15 years. This paper starts with the scientific strategy and scope of the ITPA TC Topical group and overall picture of the major progress, followed by the progress of each research field: particle transport, impurity transport, ion and electron thermal turbulent transport, momentum transport, impact of 3D magnetic fields on transport, confinement mode transitions, global confinement, and reduced transport modeling.

Summaries of research and development activities by using supercomputer system of JAEA in FY2023 (April 1, 2023 - March 31, 2024)

HPC Technology Promotion Office, Center for Computational Science & e-Systems

JAEA-Review 2024-044, 121 Pages, 2025/01

JAEA-Review-2024-044.pdf:7.42MB

Japan Atomic Energy Agency (JAEA) conducts research and development (R&D) in various fields related to nuclear power as a comprehensive institution of nuclear energy R&Ds, and utilizes computational science and technology in many activities. Over the past 10 years or so, the publication of papers utilizing computational science and technology at JAEA has accounted for about 20 percent of the total publications each fiscal year. The supercomputer system of JAEA has become an important infrastructure to support computational science and technology. In FY2023, the system was utilized in R&D activities that were prioritized in the Fourth Medium- to Long-Term Plan, including contributing to carbon neutrality through the development of innovative technologies such as improving safety, creating innovation by promoting diverse R&D related to nuclear science and technology, promoting R&D in response to the accident at TEPCO's Fukushima Daiichi Nuclear Power Station, steadily implementing technological developments for the treatment and disposal of high-level radioactive waste, and supporting nuclear safety regulatory administration and nuclear disaster prevention by promoting safety research for these purposes. This report presents a great number of R&D results accomplished by using the system in FY2023, as well as user support, operational records and overviews of the system, and so on.

Investigation of adsorption behavior of metal ions in soils

Yamaguchi, Akiko; Takahashi, Yoshio*; Okumura, Masahiko

Isotope News, (796), p.21 - 23, 2024/12

Clay minerals are abundant in soils and control the environmental behavior of various elements because they adsorb many cations. Since the strength of adsorption of clay minerals depends on the adsorption structure at the molecular level, a systematic understanding of what determines the adsorption structure at the molecular level is important. In this study, we systematically elucidated the adsorption structures of many cations, including radium, using extensive X-ray absorption fine structure (EXAFS) measurements and first-principles simulations. The results show that the size and hydration enthalpy of adsorbed ions are important in determining the adsorption structure.

Effect of carbon segregation at prior austenite grain boundary on hydrogen-related crack propagation behavior in 3Mn-0.2C martensitic steels

Okada, Kazuho*; Shibata, Akinobu*; Kimura, Yuji*; Yamaguchi, Masatake; Ebihara, Kenichi; Tsuji, Nobuhiro*

Acta Materialia, 280, p.120288_1 - 120288_14, 2024/11

https://doi.org/10.1016/j.actamat.2024.120288

Self-learning Monte Carlo with equivariant Transformer

Nagai, Yuki; Tomiya, Akio*

Journal of the Physical Society of Japan, 93(11), p.114007_1 - 114007_8, 2024/11

https://doi.org/10.7566/JPSJ.93.114007

We proposed a new self-learning Monte Carlo method using Transformer, a key technology in generative AI. By using Transformer's Attention mechanism, which can infer the relevance of distant words in a sentence, we have constructed an effective model that can efficiently capture the long-range correlations that are important in the phase transitions in electronic systems. Furthermore, we reduce the number of parameters by incorporating symmetries that the system must satisfy, such as spin rotation and spatial translation, into the network. We also found a scaling law that the loss decreases as the number of layers is increased.

Effects of magnetic ordering on the ground-state energy of plutonium dioxide; A Study using adiabatic connection fluctuation-dissipation theory

Nakamura, Hiroki; Machida, Masahiko

Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 5 Pages, 2024/11

https://doi.org/10.1115/ICONE31-134660

Efficiency and safety improvements in nuclear fuel development demand a comprehensive understanding of the thermal properties of PuO. Because of difficulty of experiments at high temperatures, they have been supplemented by numerical simulations, such as density functional theory (DFT). While DFT struggles to replicate the nonmagnetic insulating ground state of PuO, DFT+U can reproduce nonmagnetic insulating state. However, the obtained state remains less stable than magnetic states and is not the ground state. Adiabatic connection fluctuation-dissipation theory (ACFDT) is expected to be a promising solution, addressing higher-order correlations and exact exchange energies. In this study, we evaluate the ground state energy using ACFDT and find that the nonmagnetic state can be the ground state. This result successfully reproduces the observed nonmagnetic ground state of PuO and has the potential to improve predictions of the thermal properties of nuclear fuel materials.

Equivariant transformer is all you need

Tomiya, Akio*; Nagai, Yuki

Proceedings of Science (Internet), 453, p.001_1 - 001_7, 2024/11

https://doi.org/10.22323/1.453.0001

Machine learning, deep learning, has been accelerating computational physics, which has been used to simulate systems on a lattice. Equivariance is essential to simulate a physical system because it imposes a strong induction bias for the probability distribution described by a machine learning model. However, imposing symmetry on the model sometimes occur a poor acceptance rate in self-learning Monte-Carlo (SLMC). On the other hand, Attention used in Transformers like GPT realizes a large model capacity. We introduce symmetry equivariant attention to SLMC. To evaluate our architecture, we apply it to our proposed new architecture on a spin-fermion model on a two-dimensional lattice. We find that it overcomes poor acceptance rates for linear models and observe the scaling law of the acceptance rate in machine learning.

Cesium stability on the interlayers of K- or Rb-fixing micaceous minerals investigated by both experimental and numerical simulation methods

Uno, Koichiro*; Okumura, Masahiko; Nakao, Atsushi*; Yamaguchi, Akiko; Yanai, Junta*

Science of the Total Environment, 949, p.175012_1 - 175012_8, 2024/11

https://doi.org/10.1016/j.scitotenv.2024.175012

Frayed edge sites (FES), formed by the partial weathering of mica minerals, selectively adsorb Cs ions. However, the detailed mechanism of this adsorption has not been fully clarified. In this study, cation extraction and Cs adsorption experiments were conducted on mica. It was found that potassium-adsorbed mica adsorbed more Cs than rubidium-adsorbed mica. To elucidate the cause of this, the stability of Cs, rubidium, and potassium adsorbed on FES was evaluated using first-principles calculations. It was determined that the presence of potassium as the cation species prior to Cs adsorption is important for the stability of Cs on the FES.