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2026.04.14
Dr. Makoto Maeda and colleagues of the Nuclear Sensing Research Group have received the FY2025 Technical Achievement Award from the North-Kanto Branch of the Japan Atomic Energy Society of Japan for their work on the “Development of a Nondestructive Measurement Technique for Nuclear Materials in Fuel Debris.”
Quantifying the amount of nuclear material contained in fuel debris at the Fukushima Daiichi Nuclear Power Plant contributes to the streamlining of subsequent treatment and management processes. While neutron-based nondestructive measurement methods are generally effective, it is difficult to rapidly and nondestructively quantify nuclear material in large amounts of fuel debris using conventional techniques, due to the heterogeneous composition and the presence of neutron absorbers derived from control rods.
In this study, the Fast Fission neutron Coincidence Counting (FFCC) method is developed as a nondestructive assay technique that is less sensitive to neutron absorbers and applicable to fuel debris. This method evaluates the amount of nuclear material based on the fast coincidence counting of fission neutrons induced by fast neutrons. Experimental results confirmed that the method is applicable even to nuclear materials covered with neutron absorbers.
Future work will focus on further design studies through experiments and simulations, aiming for practical implementation of the method.
2026.03.30
Mr. Satoshi Nakamura, engineer of the Development Group for Nuclear Engineering Technology, received the 58th AESJ Award for Encouragement for the study entitled “Development of a Dissolution Technique for Chemical Analysis of 1F Fuel Debris and Its Application to Actual Samples“ on March 12, 2026.
Understanding the properties of the fuel debris generated by the accident at the Fukushima Daiichi Nuclear Power Station (1F) is essential for determining fuel debris retrieval methods, ensuring criticality control, managing storage, and analyzing accident progression. However, although chemical analysis of completely dissolved fuel debris is necessary to evaluate elemental and nuclide compositions—one of the key aspects of debris characterization—its high chemical stability, as indicated by previous studies, suggests that complete dissolution is extremely difficult.
In this study, we focused on an alkaline fusion method using sodium peroxide as a flux and developed an analytical technique for determining the elemental composition of fuel debris. By optimizing the processing conditions and conducting tests using TMI-2 debris, we demonstrated the effectiveness of this approach. The results were published in the Journal of Nuclear Science and Technology.
Furthermore, we applied the developed dissolution technique to fuel debris obtained from the first trial retrieval inside the pedestal of Unit 2 of 1F and succeeded in achieving complete dissolution. The major elemental and nuclide compositions obtained from the analysis of the resulting solution significantly contribute to understanding the internal conditions of the 1F reactors. These results were presented at the Autumn Meeting of the Atomic Energy Society of Japan in 2025.
The outcomes of this study are expected to serve as a valuable pretreatment method for chemical analysis throughout the long-term decommissioning process of 1F.
2026.03.19
Dr. Tatsuhiko Sato (Research fellow of the Radiation Behavior Analysis Research Group, JAEA) and his colleagues received the JNST Most Popular Article Award on March 12, 2026, for their paper “Recent improvements of the particle and heavy ion transport code system–PHITS version 3.33,” published in the Journal of Nuclear Science and Technology (J. Nucl. Sci. Technol., Vol. 61, No. 1, pp. 127-135, 2024).
PHITS (Particle and Heavy Ion Transport code System) is a general-purpose Monte Carlo radiation transport simulation code developed in Japan that can analyze the transport behavior of nearly all particles and heavy ions with high accuracy. It is widely used in a broad range of fields, including nuclear engineering, medicine, space, accelerators, and radiation protection. The award-winning paper reports recent improvements implemented in PHITS version 3.33, including enhanced consistency with nuclear data libraries, algorithmic improvements to the track-structure analysis mode, and expansions of various physical models and computational functions. These improvements have further enhanced both the accuracy and usability of PHITS, thereby broadening its range of applications.
This award recognizes the continued advancement of PHITS and the wide academic and practical impact it has had in the fields of nuclear science and radiation research.
【Awarded paper】https://doi.org/10.1080/00223131.2023.2275736
2026.01.09
Dr. Takuya Sekikawa of Research Group for Radiation Transport Analysis received Best Presentation Award in the Electronic Device category at International Symposium on Superconductivity 2025, ISS2025. The presentation title was “Energy loss functions for electronic mode of Si, Al, and TiN substrate materials used in quantum computing based on first-principles electronic structure calculations”.
The application of superconductivity for quantum computers has significantly increased its importance in recent years. At the cryogenic temperatures (10 mK to 5 K) where superconductivity is realized, it is known that environmental radiation contributes to the decay of the superconducting state. To understand this phenomenon, it is necessary to perform radiation transport calculations within superconducting materials under cryogenic conditions.
Therefore, we focused on the energy loss function under cryogenic conditions, which is fundamental data necessary for radiation transport calculations at cryogenic temperatures. The energy loss function is divided into two parts: the electronic mode, which contributes from the electronic system, and the lattice mode, which contributes from the vibration of atomic nuclei in the crystal. In this study, we first focused on the energy loss function of electronic mode. The mode determines radiation transport, and calculated energy loss functions at room temperature and cryogenic temperatures of Si, Al, and TiN, used in superconducting qubits. In the results, we confirmed that the energy loss function of the electronic mode does not vary with temperature.
In the future work, we plan to calculate energy loss function of lattice modes necessary for simulations converting the kinetic energy of ejected free electrons into thermal energy and perform radiation transport calculations in quantum computer materials. This research project is expected to contribute to the development of radiation-resistant technology for superconducting qubits.
2026.01.07
Dr. Hiromasa Nakayama, researcher of Research Group for Environmental Science, received the awarded paper at the 46th Annual Meeting of the INMM Japan Chapter. The awarded paper, “LHADDAS analysis on the area of influence of urban buildings on air dose rate distribution patterns against radiation terrorism in urban central districts” was published in the 46th Annual Meeting of the INMM Japan Chapter proceedings.
LHADDAS（Local-scale High-resolution Atmospheric Dispersion and Dose Assessment System）was conducted to analyze dose consequence of radiological agent attacks in urban central districts. The spatial distributions of the air dose rates were compared and investigated the spatial extent of the distribution patterns influenced by individual buildings by comparative analysis on the two typical cities. It was shown from the simulation results that the spatial extent of the influenced area could be about 1.0 km from a point source.
Our study can be helpful for pre-planning and practical training for responding to radioactive material dispersal attacks in urban environments.
【Awarded paper】The 46th Annual Meeting of the Institute of Nuclear Materials Management (INMM) Japan Chapter Proceedings
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