Temperature effect on radiolytically generated hydrogen yield from a plutonium nitric acid aqueous solution

Toigawa, Tomohiro; Hotoku, Shinobu; Kumagai, Yuta; Abe, Yuma*; Oyama, Kanichi*; Fukaya, Hiroyuki; Ban, Yasutoshi; Kida, Takashi; Hasegawa, Satoshi*; Nakano, Masanao*; et al.

Journal of Nuclear Science and Technology, 63(3), p.322 - 327, 2026/03

https://doi.org/10.1080/00223131.2025.2541067

The effect of temperature on hydrogen production generated from radiolysis was investigated to determine the associated implications for nuclear fuel reprocessing safety. The hydrogen yield from radiolysis of plutonium nitric acid solution was measured at temperatures up to the boiling temperature of the solution. The results showed no notable temperature dependence even under boiling conditions. The impact of solution agitation on hydrogen production was also assessed, which revealed minor differences in the hydrogen yield between static and agitated conditions at room temperature. These findings suggest that high temperatures or boiling the solution do not considerably enhance hydrogen generation, and provide crucial information for accurately modeling hydrogen risks under severe accidents.

Run function confirmation of the quadrupedal robots in JAEA facilities targeted for act on special measures concerning nuclear emergency preparedness

Watanabe, Kaho; Nishiyama, Yutaka; Imahashi, Masaki; Taguchi, Yuji; Iitsuka, Yoshinobu; Ouchi, Takuya; Inoue, Shuichi; Kozawa, Takayuki; Nemoto, Takahiro; Sugaya, Takashi; et al.

JAEA-Testing 2025-001, 56 Pages, 2025/11

JAEA-Testing-2025-001.pdf:2.61MB

There is an emergency response team against 7 nuclear facilities (JRR-3 in Nuclear Science Research Institute, Tokai Reprocessing Plant (TRP) in Nuclear Fuel Cycle Engineering Laboratories, JMTR, HTTR and Joyo in Oarai Research and Development Institute, Prototype Fast Breeder Reactor Monju, Fugen Decommissioning Engineering Center) accidents of Japan Atomic Energy Agency (JAEA). The team is in Naraha Center for Remote Control Technology Development (NARREC). On site surveys which are about the situations and the access entering route of the 7 site emergencies were conducted by the team in 2021. And the results of the surveys made the team get two Spot (quadrupedal robots) in 2022. This is because the team thought using Spot gave operators the less exposure than using crawler robots which had been belonged to the team. After that it was confirmed that the Spot have the ability to respond to the emergency on the route of each facility in 2023. This report shows the results of the Spot's run function (= shooting videos, running oversteps, running up and down stairs, and so on) confirmation about 6 facilities (JRR-3, JMTR, HTTR, Joyo, Monju and Fugen).

None

Nagata, Shuhei*; Ogawa, Yusuke*; Suzuki, Satoru*; Igarashi, Takahiro; Nagaoka, Toru*; Mitsui, Seiichiro; Watanabe, Yutaka*; Nishikata, Atsushi*

NUMO-TR-25-03, p.46 - 51, 2025/10

no abstracts in English

Atomization mechanisms in the vortex-like flow of a wall-impinging jet in a shallow pool

Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*

Physics of Fluids, 37(3), p.033333_1 - 033333_20, 2025/03

https://doi.org/10.1063/5.0253743

In a severe accident, as molten fuel is assumed to behave as a wall-impinging jet in a shallow coolant pool, atomize and accumulate as fuel debris, it is important to reveal the atomization mechanisms of the wall-impinging jet. This study aimed to reveal the atomization mechanisms in the vortex-like flow of a wall-impinging jet in a shallow pool of a liquid-liquid system, focusing on droplet formation as an elementary process of atomization. To quantitatively investigate these mechanisms, we applied quantification methods to three-dimensional interfacial data obtained by a previous experimental study using three-dimensional laser-induced fluorescence with index matching. Detailed observations of the spreading behavior of droplets and vortex-like flow, along with quantitative estimations, found out that the vortex-like flow is the dominant source of droplets on the atomization. Further investigations into the forces acting on the vortex-like flow found out the formation and collapse processes of the vortex-like flow. The accelerations of the normal forces acting on the vortex-like flow can be represented by superficial centrifugal acceleration and gravitational acceleration. Our next analysis focused on investigating droplet formation as the elementary process of atomization. The results showed two droplet formation patterns: liquid-film breaking patterns, wherein droplets directly form from the liquid film, and the surfing pattern, wherein droplets form from interfacial waves on the liquid film. Subsequently, the droplet data were grouped using dimensionless numbers and compared with theoretical lines describing the different droplet formation mechanisms. This comparison revealed the mechanisms of droplet formation within the vortex-like flow.

An Evaluation on Inelastic Thermal Neutron Scattering Cross-Section Data of Crystalline Graphite

Okita, Shoichiro; Abe, Yutaka*; Tasaki, Seiji*; Fukaya, Yuji

Radioisotopes, 73(3), p.233 - 240, 2024/11

https://doi.org/10.3769/radioisotopes.73.233

Selective resonance ionization of odd calcium isotopes using linearly polarized lasers

Iwata, Yoshihiro; Miyabe, Masabumi; Wells, S. R.*; Yamamoto, Yuta*; Hasegawa, Shuichi*

Proceedings of International Topical Workshop on Fukushima Decommissioning Research 2024 (FDR2024) (Internet), 4 Pages, 2024/10

In this study, triple and double resonance ionization schemes of atomic Ca were developed, aiming for the separation of odd isotopes by (i) laser polarization-dependent selection rules, and (ii) large isotope shifts of odd Ca isotopes in the Rydberg levels. Separation of odd isotopes was confirmed under the orthogonal condition. Suppression of non-resonant ionization of Ca by the electric field in the ionization region could further improve the optical isotope selectivity of Ca.

Structure of drifting snow simulated by Lagrangian particle dispersion model coupled with large-eddy simulation using the lattice Boltzmann method

Watanabe, Tsutomu*; Ishikawa, Shuhei*; Kawashima, Masayuki*; Shimoyama, Ko*; Onodera, Naoyuki; Hasegawa, Yuta; Inagaki, Atsushi*

Journal of Wind Engineering and Industrial Aerodynamics, 250, p.105783_1 - 105783_17, 2024/07

https://doi.org/10.1016/j.jweia.2024.105783

This paper presents simulations of drifting snow using a Lagrangian particle dispersion model coupled with a large-eddy simulation code. The model accurately replicates observed features such as mass transport rate dependency on flow velocity and variations in particle size distribution. It also shows that the saltation layer height increases monotonically with flow velocity, contrary to conventional estimates. Additionally, the study confirms the transition from saltation to suspension near the estimated saltation layer height and finds that dense snow streamers are linked to small-scale low-speed streaks in near-surface flows.

Current numbers of qubits and their uses

Ichikawa, Tsubasa*; Hakoshima, Hideaki*; Inui, Koji*; Ito, Kosuke*; Matsuda, Ryo*; Mitarai, Kosuke*; Miyamoto, Koichi*; Mizukami, Wataru*; Mizuta, Kaoru*; Mori, Toshio*; et al.

Nature Reviews Physics (Internet), 6(6), p.345 - 347, 2024/06

https://doi.org/10.1038/s42254-024-00725-0

Production rates of long-lived radionuclides Be and Al under direct muon-induced spallation in granite quartz and its implications for past high-energy cosmic ray fluxes

Sakurai, Hirohisa*; Kurebayashi, Yutaka*; Suzuki, Soichiro*; Horiuchi, Kazuho*; Takahashi, Yui*; Doshita, Norihiro*; Kikuchi, Satoshi*; Tokanai, Fuyuki*; Iwata, Naoyoshi*; Tajima, Yasushi*; et al.

Physical Review D, 109(10), p.102005_1 - 102005_18, 2024/05

https://doi.org/10.1103/PhysRevD.109.102005

Secular variations of galactic cosmic rays (GCRs) are inseparably associated with the galactic activities and should reflect the environments of the local galactic magnetic field, interstellar clouds, and nearby supernova remnants. The high-energy muons produced in the atmosphere by high-energy GCRs can penetrate deep underground and generate radioisotopes in the rock. As long lived radionuclides such as Be and Al have been accumulating in these rocks, concentrations of Be and Al can be used to estimate the long-term variations in high-energy muon yields, corresponding to those in the high-energy GCRs over a few million years. This study measured the production cross sections for muon induced Be and Al by irradiating positive muons with the momentum of 160 GeV/c on the synthetic silica plates and the granite core at the COMPASS experiment line in CERN SPS. In addition, it the contributions of the direct muon spallation reaction and the nuclear reactions by muon-induced particles on the production of long lived radionuclides in the rocks were clarified.

Spin dependence in the -wave resonance of +

Okudaira, Takuya*; Nakabe, Rintaro*; Auton, C. J.*; Endo, Shunsuke; Fujioka, Hiroyuki*; Gudkov, V.*; Ide, Ikuo*; Ino, Takashi*; Ishikado, Motoyuki*; Kambara, Wataru*; et al.

Physical Review C, 109(4), p.044606_1 - 044606_9, 2024/04

https://doi.org/10.1103/PhysRevC.109.044606