Real-time inversion of radioactive source distribution using air dose rate measurements via least absolute shrinkage and selection operator method

Shi, W.*; Machida, Masahiko; Okamoto, Koji*; Luo, X.*; Feng, W.*; Liu, X.*

Reliability Engineering & System Safety, 272, Part1, p.112538_1 - 112538_18, 2026/08

http://doi.org/10.1016/j.ress.2026.112538

The reliability of emergency response in severe nuclear accidents critically depends on robust real-time monitoring of radioactive source distributions. However, this safety function is challenged by physical constraints that create monitoring blind spots and by the inadequacy of static methods in tracking dynamic releases. To enhance the reliability and robustness of source term estimation, this study proposes a dynamic reconstruction framework based on LASSO regression with temporal regularization. A sliding-window time-penalty mechanism is introduced, imposing -norm constraints on inter-step source variations to ensure physical continuity. The contribution matrix and measurement vector are normalized to counteract biases from radiation shielding and time-varying intensities. Validation using a two-room model with internal shielding, with PHITS Monte Carlo simulation, demonstrates accurate reconstruction of dynamic sources from remote measurements. Temporal regularization enhances situational awareness by suppressing spatial aliasing: at sliding-window width (no regularization), hotspot locations fluctuate significantly, with quantitative mean absolute error fluctuations at around , whereas yields improved spatial consistency and the fluctuation quantities decrease to the range. Comparative analysis identifies as optimal in balancing accuracy and computational cost. This work establishes a more reliable pathway for dynamic hazard assessment, enabling accurate localization and intensity tracking under challenging conditions. The proposed framework provides a decision-support tool enhancing the resilience and safety of emergency management in nuclear facilities.

Implementation of ideal cascade model for uranium enrichment to nuclear fuel cycle simulator

Abe, Takumi; Suzuki, Taiga*; Okamura, Tomohiro*; Nakase, Masahiko*

Annals of Nuclear Energy, 232, p.112224_1 - 112224_7, 2026/07

https://doi.org/10.1016/j.anucene.2026.112224

NMR evidence for full-gap spin-triplet superconducting state in UBe

Minami, Shoko*; Matsuno, Haruki*; Morita, Kyohei*; Matsuki, Rintaro*; Kotegawa, Hisashi*; Harima, Hisatomo*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*; Tou, Hideki*

Journal of the Physical Society of Japan, 95(7), p.074711_1 - 074711_11, 2026/07

https://doi.org/10.7566/JPSJ.95.074711

Measurements of neutron capture cross-sections for nuclides of interest in decommissioning (V); Zr(n, )Zr and Zr(n, )Zr reactions at JRR-3

Nakamura, Shoji; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.; Shibahara, Yuji*

Journal of Nuclear Science and Technology, 63(6), p.653 - 666, 2026/06

https://doi.org/10.1080/00223131.2025.2586632

Neutron capture cross-section measurements at TC-Pn in KUR for tungsten among nuclides in decommissioning

Nakamura, Shoji; Shibahara, Yuji*; Kimura, Atsushi; Endo, Shunsuke; Rovira Leveroni, G.

KURNS Progress Report 2025, P. 101, 2026/06

https://adm.rri.kyoto-u.ac.jp/pub/progressrep2/

no abstracts in English

Permeability and Forchheimer coefficient of packed beds with different particles sizes

Kawabe, Tomosaburo*; Sano, Yoshihiko*; Kuwahara, Fujio*; Uesawa, Shinichiro; Yoshida, Hiroyuki

Dai-63-Kai Nihon Dennetsu Shimpojiumu Koen Rombunshu (Internet), 1 Pages, 2026/05

To estimate the thermal behavior of fuel debris inside the Primary Containment Vessels (PCVs) of TEPCO's Fukushima Daiichi Nuclear Power Station, a simulation method has been developed using the JUPITER code with porous medium models. However, it has been found that the selection of models and parameters according to the internal structure of the porous media significantly affects the accuracy of simulation results, highlighting the need for appropriate model selection strategies. In this study, we focus on packed beds with particles as one form of porous media and investigate a methodology for determining model parameters that characterize their flow behavior. Systematic knowledge of packed beds with heterogeneous particle size ratios and packing structures remains limited, and comprehensive organization accounting for structural differences has not yet been fully established. Therefore, numerical simulations were employed to evaluate the permeability and Forchheimer coefficient of packed beds with different particle size ratios and packing structures. Based on the obtained results, a method for appropriately determining these parameters according to the structural characteristics of packed beds is proposed, and insights are provided that contribute to improving the accuracy of flow analysis models in porous media.

Kinetic and thermodynamic controls on CsI-Mo gas-phase reactions under varying oxygen potentials

Shiotsu, Hiroyuki

Progress in Nuclear Energy, 195, p.106300_1 - 106300_11, 2026/05

https://doi.org/10.1016/j.pnucene.2026.106300

Reconsideration of numerical model for hydrogen thermal desorption spectra of iron with hydrogen-enhanced strain-induced vacancies

Ebihara, Kenichi; Yamaguchi, Masatake; Itakura, Mitsuhiro

Metallurgical and Materials Transactions A, 57(4), p.1480 - 1489, 2026/04

https://doi.org/10.1007/s11661-026-08146-7

Hydrogen (H) embrittlement is an important issue for steel. The experimental thermal desorption spectra of H from an iron sample containing H-enhanced strain-induced vacancies (Vs) were successfully reproduced by revising a previous numerical model. In the revised model, we adopted concentration variables for Vs and V clusters, which are distinguished by the number of trapped H atoms. This revision eliminated the assumption of V and V cluster migration, required in the original model. Simulation results of the revised model revealed that the spike-like desorption on the peak attributed to Vs and V clusters in the spectra simulated by the original model was an artifact caused by the assumption. In addition, it was suggested that V clusters can exist other than Vs in the specimens after deformation with H charging. It is considered that the revised model is a useful framework for studying Vs and V clusters under H-affected conditions.

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2024 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2025-013, 206 Pages, 2026/03

JAEA-Technology-2025-013.pdf:34.64MB

This report presents results of the investigations on the distribution-mapping project of radioactive substances conducted in FY2024. Car-borne and walk surveys, a measurement using survey meters, and an unmanned helicopter survey were carried out to obtain air dose rate data on land to create their distribution maps, and temporal changes of those air dose rates were analyzed. In order to confirm the applicability of unmanned aircraft to monitoring in mountainous areas, a basic performance of unmanned aircraft was investigated in mountainous areas. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. These measurement results were published on the WEB site. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated air dose rate distribution data acquired through surveys such as car-borne and walk surveys. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out. Representative life patterns that can be expected after the return to the evacuation-designated restricted area were set, and the cumulative exposure doses were evaluated for the local governments and residents in the area. Score maps to classify the importance of the measurement points were created, and the temporal changes in the score were analyzed. A system to report the tritium concentration level in seawater to the Nuclear Regulation Authority was operated, and the variation of tritium concentration before and after the discharge of ALPS treated water to the ocean was analyzed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until FY2024 was analyzed.

Random singlet physics in the pyrochlore antiferromagnet NaCdCuF

Kancko, A.*; Sakai, Hironori; Tokunaga, Yo; Colman, R. H.*; 6 of others*

Physical Review Research (Internet), 8(1), p.013344_1 - 013344_11, 2026/03

https://doi.org/10.1103/rw5c-491w