Development of 1D-CFD coupling method for natural circulation analyses through benchmark analyses of shutdown heat removal tests in EBR-II

Yoshimura, Kazuo; Doda, Norihiro; Tanaka, Masaaki; Fujisaki, Tatsuya*; Murakami, Satoshi*

Annals of Nuclear Energy, 226, p.111896_1 - 111896_11, 2026/02

https://doi.org/10.1016/j.anucene.2025.111896

At the Japan Atomic Energy Agency, a multilevel simulation (MLS) methodology which enables consistent evaluation from whole plant behavior to local phenomena in the plant components is being developed to attempt plant design and enhance the safety of sodium-cooled fast reactors. To validate the coupling method in the MLS system, the 1D-CFD coupling method using Super-COPD for 1D plant dynamics analysis and Fluent for multi-dimensional CFD analysis was applied to the analyses of loss of flow tests in EBR-II. It was confirmed that it could predict multi-dimensional thermal-hydraulic phenomena such as thermal stratification in the upper plenum, Z-shaped pipe, and cold pool, holding the whole plant behavior simultaneously. Moreover, the applicability of the 1D-CFD coupling method to the evaluation of the phenomena in natural circulation conditions was confirmed by comparing the results of the 1D-CFD couple analyses and the measured data.

Benchmarks of iron nuclear data for fusion neutron sources

Kwon, Saerom*; Konno, Chikara; Honda, Shogo*; Kenjo, Shunsuke*; Sato, Satoshi*

Fusion Engineering and Design, 223, p.115548_1 - 115548_8, 2026/02

https://doi.org/10.1016/j.fusengdes.2025.115548

In order to evaluate the accuracy of the iron data in the latest nuclear data libraries (FENDL-3.2b, JENDL-5, ENDF/B-VIII.0 and JEFF-3.3) used in the fusion neutron source design, we performed their benchmark tests by using QST/TIARA iron experiment with quasi mono-energy neutrons of 40 and 65 MeV and JAEA/FNS iron experiment with DT neutrons. From the test results, we have found the following issues; (1) The calculation results with FENDL-3.2b underestimate the measured neutron fluxes of the continuous energy range (10-60 MeV) by a factor of 0.6 in the TIARA experiment with 65 MeV neutrons; (2) The calculation results with FENDL-3.2b tend to underestimate the measured neutron flux above 10 MeV by a factor of 0.8 at depth of 70 cm and overestimate the measured ones below 10 keV by a factor of 1.3 up to depth of 40 cm in the FNS experiment. We investigated those issues in detail and clarified their reasons.

Validation of underwater radiation monitoring detector

Ji, W.*; Lee, E.*; Ji, Y.-Y.*; Ochi, Kotaro; Yoshimura, Kazuya; Funaki, Hironori; Sanada, Yukihisa

Nuclear Engineering and Technology, 58(2), p.103933_1 - 103933_6, 2026/02

https://doi.org/10.1016/j.net.2025.103933

We aimed to validate the performance of an in situ underwater radiation detector, MARK-U1 (Monitoring of Ambient Radiation of KAERI - Underwater), was used to estimate Cs activity concentration in river and reservoir sediment at predicted sites of contamination. Additionally, underwater core samples were collected to measure the radioactivity using a high-purity germanium (HPGe) detector. To estimate radioactivity, a conversion factor was derived by comparing the measured spectrum and Cs activity in the sample. A Monte Carlo N-Particle (MCNP) simulation was conducted to determine the effective source geometry for in situ measurement. The simulation results correlated well with the on-site MARK-U1 monitoring results, with a deviation of 31.62%. These findings validate the performance of the in situ detector. This device can therefore be used to estimate Cs activity concentration in the underwater sediment via on-site monitoring, without requiring sample collection.

End-to-end discriminative representation learning for fault diagnosis in safety-critical time series

Dong, F.*; Xiao, Y.*; Chen, S.*; Demachi, Kazuyuki*; Takaya, Shigeru; Yoshikawa, Masanori

Advanced Engineering Informatics, 69(Part D), p.104094_1 - 104094_23, 2026/01

https://doi.org/10.1016/j.aei.2025.104094

Residual stress relief effect in gradient structural steel and remaining life evaluation under stochastic fatigue loads

Qin, T. Y.*; Hu, F. F.*; Xu, P. G.; Zhang, R.*; Su, Y. H.; Ao, N.*; Li, Z. W.*; Shinohara, Takenao; Shobu, Takahisa; Wu, S. C.*

International Journal of Fatigue, 202, p.109233_1 - 109233_16, 2026/01

https://doi.org/10.1016/j.ijfatigue.2025.109233

Role of biotite content and structure in controlling cesium diffusion in granitic rocks

Fukatsu, Yuta; Hu, Q.*; Tachi, Yukio

Journal of Contaminant Hydrology, 276, p.104789_1 - 104789_12, 2026/01

https://doi.org/10.1016/j.jconhyd.2025.104789

A Thermodynamic study of fluorite/bixbyite equilibria in the UO-PuO-PuO system

Vinograd, V. L.*; Vauchy, R.

Journal of Nuclear Materials, 619, p.156244_1 - 156244_16, 2026/01

https://doi.org/10.1016/j.jnucmat.2025.156244

Thermodynamic properties of (UPu)O fluorite (FCC) and (UPu)O bixbyite (BCC) in the UO-PuO-PuO system are assessed by considering phase equilibrium constraints and data on the variation of oxygen to metal ratio (O/M) as a function of the chemical potential of O. Thermodynamically, both BCC and FCC are described as ordered solid solutions allowing for a decrease in the configurational entropy of their oxygen/vacancy distributions at the specific values of = -0.5 and = -0.375 (O/M = 1.5 and O/M = 1.625). With this approach, fluorite/bixbyite equilibria in PuO-PuO and in UO-PuO-PuO are reproduced well with little effort. Moreover, we show that a large manifold of experimental data on the UO-PuO-PuO system is consistent with the assumption that Pu/(Pu+U) ratios in individual phases remain equal to the total Pu/(Pu+U) ratio in the system, i.e., no inter-phase U/Pu-partitioning occurs.

Development of LASSO based optimized scheme for reconstructing radioactive source distributions using monitoring air dose rates

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Okamoto, Koji*

Measurement, 258(Part D), p.119444_1 - 119444_15, 2026/01

https://doi.org/10.1016/j.measurement.2025.119444

Experimental study of AESOP code for aerosol removal behavior from a rising gas bubble in water pool and parametric study for application to sodium pool system

Miyahara, Shinya*; Koie, Ryusuke*; Uno, Masayoshi*; Kawaguchi, Munemichi*; Sato, Rika; Seino, Hiroshi

Nuclear Engineering and Design, 446(Part A), p.114523_1 - 114523_14, 2026/01

https://doi.org/10.1016/j.nucengdes.2025.114523

Random media criticality analysis using randomized Fourier series and incomplete randomized Weierstrass function

Ueki, Taro

Progress in Nuclear Energy, 191, p.106007_1 - 106007_11, 2026/01

https://doi.org/10.1016/j.pnucene.2025.106007

Criticality analysis of continuously mixed random media is crucial for safely retrieving fuel debris. Initially, a Monte Carlo method was established using the Incomplete Randomized Weierstrass Function (IRWF) to model a single-mode inverse power law power spectrum. However, image analysis showed that oxide debris mock-ups require a more complex model. To address this, a new function called the Randomized Fourier Series (RFS) was developed to represent arbitrary power spectra. RFS is versatile, incorporating Brownian motion models and aiding reactor physicists in analyzing various scenarios. Numerical results compare the fluctuation of neutron multiplication factor in various media generated by RFS and IRWF, identifying the spectral range most affecting k.