Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2026)

Asamori, Koichi; Sueoka, Shigeru; Komatsu, Tetsuya; Ogata, Manabu; Uchida, Mao; Nishiyama, Nariaki; Tanaka, Kiriha; Akiyama, Reina; Kobayashi, Tomoharu; Mitsuguchi, Takehiro; et al.

JAEA-Review 2026-028, 29 Pages, 2026/09

JAEA-Review-2026-028.pdf:1.05MB

This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2026. The objectives and contents of this research are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques.

Trade-off between adsorption capacity and binding strength regulates carbon stabilization in mineral-associated organic matter

Sun, R.; Abe, Yukiko; Atarashi-Andoh, Mariko; Koarashi, Jun

Soil Biology & Biochemistry, 218, p.110150_1 - 110150_12, 2026/07

https://doi.org/10.1016/j.soilbio.2026.110150

The role of minerals in soil carbon sequestration has been increasingly recognized. However, the mechanism by which mineral-associated organic matter (MAOM) resists microbial decomposition remains an open question. We prepared MAOM on amorphous allophane and crystalline kaolinite with different organic matter (OM) proxies, characterized the affinity strength of these associations using isothermal titration calorimetry and X-ray photoelectron spectroscopy, and quantified their microbial mineralization through aerobic incubation. We found that amorphous allophane displayed greater OM adsorption capacity due to its higher specific surface area; in contrast, crystalline kaolinite exhibited stronger binding with OM, consistent with its predominant inner-sphere complexation. Furthermore, lower MAOM mineralization was found corresponding to higher Langmuir affinity. This inverse relationship was more pronounced than the correlation with the amount of OM adsorbed by minerals. These findings suggest that the overall MAOM stability is controlled by a balance between binding strength and adsorption capacity. Namely, stronger binding affinity enhances microbial resistance of MAOM, while the abundance of mineral sites determines the amount of MAOM accessible for microbial decomposition. This study presents a novel mechanistic understanding of the MAOM dynamics and refines the prevailing perspective on MAOM persistence.

Hydrogen in the Earth core inferred from neutron imaging and diffraction

Takahashi, Naoki*; Sakamaki, Tatsuya*; Hattori, Takanori; Funakoshi, Kenichi*; Arima-Osonoi, Hiroshi*; Sano, Asami; Abe, Jun*; Suzuki, Akio*

Scientific Reports (Internet), 16, p.14162_1 - 14162_13, 2026/05

https://doi.org/10.1038/s41598-026-49969-z

We performed high-pressure and high-temperature neutron diffraction and imaging experiments in situ to determine the hydrogen content in liquid iron. We observed that liquid iron contains 0.17(3) wt.% H at 3.4 GPa and 1400 K, indicating that liquid iron is hydrogenated in the magma ocean during core formation. For the hydrogen content in the liquid iron at the base of the magma ocean, we estimated that the outer and inner cores contain 0.60-0.72 and 0.30-0.44 wt.% H, corresponding to 70-85 and 1.9-2.7 times the mass of hydrogen in the ocean, respectively. This suggests that hydrogen can contribute more than half of the density deficit in the outer core. For the magma ocean equilibrating with the hydrogen-rich primary atmosphere, the study findings show that liquid iron plays a crucial role in transporting a large amount of hydrogen into the core.

J-PARC LINAC 50 Hz operation verification study

Kondo, Yasuhiro; Chimura, Motoki; Cicek, E.*; Fukui, Yuji*; Futatsukawa, Kenta*; Fuwa, Yasuhiro; Goto, Rikuto*; Hirano, Koichiro; Ishikawa, Masaki*; Ito, Takashi; et al.

Proceedings of 22nd Annual Meeting of Particle Accelerator Society of Japan (Internet), p.124 - 129, 2026/03

https://www.pasj.jp/web_publish/pasj2025/proceedings/PDF/FRO6/FRO601.pdf

Various upgrade plans of the J-PARC linac are underway, and repetition-rate doubling project is one of the most important part. Currently, the linac supplies a 400~MeV H ion beam to the 3~GeV synchrotron (RCS) at a repetition rate of 25~Hz. However, to deliver the beam to both RCS and proton-beam irradiation facility under planning, it is necessary to raise the repetition rate from 25~Hz to 50~Hz. Prior to construction of the beamline to the irradiation facility, we conducted a verification of the 50~Hz operation of all the linac apparatus simultaneously within the current operational limits in May 2025. And also, the verification of the 50~Hz operation of the particle counter system, which is one of the most important safety device of the J-PARC accelerator, was conducted. As a result, any significant problems were not found out, and it is now ready for the upcoming 50~Hz-beam acceleration demonstration. This paper describes this details of the demonstration of the 50~Hz operation, without beam acceleration, of the J-PARC linac.

Microbial survivability during repeated extreme dry-wet cycles determines CO emissions after rewetting of dried soils in humid temperate forests

Nakayama, Masataka*; Suzuki, Yuri; Abe, Yukiko; Taniguchi, Takeshi*; Atarashi-Andoh, Mariko; Koarashi, Jun; Nagano, Hirohiko*

Biogeochemistry, 169(2), p.15_1 - 15_15, 2026/02

https://doi.org/10.1007/s10533-026-01310-6

Possible transition from silandic to aluandic andosols with acidification as evidenced by detailed profile investigation of two well-preserved forest andosols in Japan

Alam, M. M.*; Yamakita, Eri*; Inoue, Yuzuru*; Koarashi, Jun; Atarashi-Andoh, Mariko; Abe, Yukiko; Nakayama, Masataka*; Mori, Yuki*; Hiradate, Shuntaro*

Soil Science and Plant Nutrition, 72(1), p.55 - 66, 2026/01

https://doi.org/10.1080/00380768.2025.2511803

Phase diagram of the polystyrene/near-critical water system

Shibata, Motoki*; Takenaka, Mikihito*; Motokawa, Ryuhei; Kumada, Takayuki; Ueda, Yuki; Miyazaki, Tsukasa*; Nakanishi, Yohei*; Abe, Jun*; Iwase, Hiroki*; Shibayama, Mitsuhiro*; et al.

Polymer, 340, p.129203_1 - 129203_7, 2025/12

https://doi.org/10.1016/j.polymer.2025.129203

Progress in linac beam commissioning for high-intensity operations for J-PARC power upgrades

Liu, Y.*; Otani, Masashi*; Miyao, Tomoaki*; Nakazawa, Yuga*; Shibata, Takanori*; Nammo, Kesao*; Fang, Z.*; Futatsukawa, Kenta*; Fukui, Yuji*; Mizobata, Satoshi*; et al.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.855 - 857, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-TUAD1

Pressure-driven solid-state radical polymerization toward carbon nanothread

Che, G.*; Tang, X.*; Liu, J.*; Lang, P.*; Fei, Y.*; Yang, X.*; Wang, Y.*; Gao, D.*; Wang, X.*; Ju, J.*; et al.

Nano Letters, 25(39), p.14467 - 14472, 2025/09

https://doi.org/10.1021/acs.nanolett.5c03977

Mechanochemical radical polymerization has unique advantages in the synthesis of polymer due to its reduced solvent consumption and adaptability of insoluble monomers. However, it suffers from the uncontrollable degradation of the formed polymers during reaction and new synthetic strategy with precise controllability needs to be developed. Here, by employing high static pressure up to 30 GPa, we found 1,3,5-trifluorobenzene undergoes radical polymerization by breaking the conjugated -bonds, and forms a carbon nanothread with high selectivity (Polymer-I polymorph). Based on the crystal structure at the threshold pressure and the calculated energy barriers for the bonding pathway, we concluded that the benzene-rings react via a 1-2 radical polymerization pathway. Our work highlights high pressure is a robust method to initiate the solid-state radical polymerization, even for very stable aromatics, and offers fresh insights for the synthesis of polymeric carbon-based materials with high selectivity.

Evaluating the effect of temporal variations in wind speed on sheltering effectiveness and developing a simplified correction method to account for these variations

Hirouchi, Jun; Takahara, Shogo; Watanabe, Masatoshi*

Journal of Radiological Protection, 45(2), p.021506_1 - 021506_13, 2025/05

https://doi.org/10.1088/1361-6498/add53e

Sheltering is a key countermeasure for mitigating radiation exposures during nuclear power plant accidents. The effectiveness of sheltering in minimizing inhalation exposure is commonly expressed using the reduction factor, which is the ratio of indoor to outdoor cumulative doses. The indoor dose is primarily influenced by the air exchange rate, penetration factor, and indoor deposition rate. Additionally, the air exchange rate is dependent on wind speed. In previous studies, the reduction factor was often treated as a constant value or calculated under constant wind speed conditions. However, wind speed varies in reality. This study investigated the effect of temporal variations in wind speed on the reduction factor and developed a simplified correction method to account for these variations. The results revealed that temporal variations in wind speed caused the reduction factor to differ by a factor of approximately two. Using the simplified correction method, the corrected reduction factors agreed, on average, within 10% of those calculated using a method that explicitly considers temporal variations in actual wind speed. Additionally, the computational cost was reduced by more than 20 times.