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).

Compliance measures at the Radioactive Waste Treatment Facilities at the Nuclear Science Research Institute; Aseismic reinforcement of the Radioactive Waste Treatment Facility No. 3, Waste Size Reduction and Storage Facility, and Waste Volume Reduction Facility

Iketani, Shotaro; Suzuki, Takeshi; Yokobori, Tomohiko; Sugawara, Satoshi; Yokota, Akira; Kikuchi, Genta; Muraguchi, Yoshinori; Kitahara, Masaru; Seya, Manato; Kurosawa, Tsuyoshi; et al.

JAEA-Technology 2025-001, 169 Pages, 2025/08

JAEA-Technology-2025-001.pdf:14.22MB

The radioactive waste treatment facilities at the Nuclear Science Research Institute includes the Radioactive Waste Treatment Facility No. 3, Waste Size Reduction and Storage Facility, and Waste Volume Reduction Facility. These three facilities come under the purview of the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors, and are included under Class C of the act based on the seismic requirements specified in the Act. We assessed the seismic capacity of these three radioactive waste treatment facilities based on the current Building Standards Act, to verify whether they comply with the new regulatory requirements enforced by the Nuclear Regulation Authority (NRA) in the aftermath of the 2011 nuclear accident at the Fukushima Daiichi Nuclear Power Station operated by the Tokyo Electric Power Company. We found that the allowable stress of a few structural members used in the construction of the facilities did not meet the regulatory requirements. After studying the approval granted by the NRA for the construction plans, including the design and construction methods (design and construction plans) of the three facilities on March 5, 2021, we made aseismic reinforcement at these facilities between 2021 and 2022. This report presents an overview of the seismic design of these facilities and an outline of the aseismic reinforcement conducted, management system existing, safety measures adopted, and the preoperational inspections conducted at these facilities.

Thermal conductivity evaluation of Am-doped oxide fuels

Yokoyama, Keisuke; Watanabe, Masashi; Onishi, Takashi; Yano, Yasuhide; Tokoro, Daishiro*; Sugata, Hiromasa*; Kato, Masato*

JAEA-Research 2025-002, 18 Pages, 2025/05

JAEA-Research-2025-002.pdf:1.73MB

It is advocated as a development target of fast reactors (FRs) to allow for the of use of mixed oxide (MOX) fuels containing minor actinide (MA) separated and recovered from spent fuels with the aim of reducing the volume and toxicity of high-level radioactive waste generated from nuclear reactors. In the development of MAMOX fuels, it is important behavior to understand the thermal properties such as thermal conductivity for fuel design and analysis of the irradiation. However, there are only a few reports on the thermal properties of MA-MOX fuels, and neither the effects of MA contents nor of oxygen non-stoichiometry in MOX fuels on their thermal conductivities have been fully understood. In this study, the thermal conductivities of MOX fuels with up to 15% Am content were measured at near-stoichiometric composition and the relationship between thermal conductivity and Am content was evaluated. Moreover, the thermal conductivities of Am-doped UO fuels were also measured and evaluated by comparison with Am-MOX to evaluate the effect of Am content. The fuel samples used in this study were three types of MOX with a Pu content of 30% and different Am contents (5%, 10%, and 15%), and UO containing 15% Am. The thermal conductivities of specimens were calculated from the thermal diffusivities measured by the laser flash method, the density of the specimens and, the heat capacity at constant pressure. The oxygen partial pressure during the measurement was controlled at that of the targeted near-stoichiometric composition. The thermal conductivities of all specimens exhibited a decline with increasing temperature and Am content, with a particularly pronounced reduction observed below 1,173 K. The results of the classical phonon scattering model analysis of the measured thermal conductivities showed that the effect of lattice strain due to the Am addition was significant on the thermal resistivity change, and the effect was comparable for both MOX and UO.

Effect of Am addition on oxygen potential in (UPuAm)O

Yokoyama, Keisuke; Watanabe, Masashi; Usui, Akane; Seki, Takayuki*; Onishi, Takashi; Kato, Masato

Nuclear Materials and Energy (Internet), 42, p.101908_1 - 101908_6, 2025/03

https://doi.org/10.1016/j.nme.2025.101908

Oxygen potential of high Am content MOX, (UPuAm)O, was measured at 1273 K, 1473 K, 1573 K, and 1623 K. by gas equilibrium method using thermogravimeter. Comparing the measured data with the literature data, it was found that the addition of 15% Am increases the oxygen potential of (U, Pu)O by 100-150 kJ/mol for the same Pu content and O/M ratio. The proportion of cations in the stoichiometric composition was determined as (UUPuAm)O, assuming the presence of Am and partial oxidation of U to U. The relationship between oxygen partial pressure and deviation x from stoichiometry in (UPuAm)O was analyzed by defect chemistry model. The equation to represent the O/M ratio was derived as a function of temperature and oxygen partial pressure. A part of this study includes the results of MEXT Innovative Nuclear Research and Development Program Grant Number JPMXD0219214921.

Difference in accumulation of plutonium and curium isotopes formed in americium targets irradiated in Joyo and JMTR

Onishi, Takashi; Koyama, Shinichi*; Yokoyama, Keisuke; Morishita, Kazuki; Watanabe, Masashi; Maeda, Shigetaka; Yano, Yasuhide; Oki, Shigeo

Nuclear Engineering and Design, 432, p.113755_1 - 113755_17, 2025/02

https://doi.org/10.1016/j.nucengdes.2024.113755

France-Japan collaboration on severe accident studies in sodium-cooled fast reactors, 2; Methodologies and calculations of severe accident phases

Sogabe, Joji; Ishida, Shinya; Tagami, Hirotaka; Okano, Yasushi; Kamiyama, Kenji; Onoda, Yuichi; Matsuba, Kenichi; Yamano, Hidemasa; Kubo, Shigenobu; Kubota, Ryuzaburo*; et al.

Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10

In the frame of France-Japan collaboration, the calculational methodologies were defined and assessed, and the phenomenology and the severe accident consequences were investigated in a pool-type sodium-cooled fast reactor.

Single-shot laser-driven neutron resonance spectroscopy for temperature profiling

Lan, Z.*; Arikawa, Yasunobu*; Mirfayzi, S. R.*; Morace, A.*; Hayakawa, Takehito*; Sato, Hirotaka*; Kamiyama, Takashi*; Wei, T.*; Tatsumi, Yuta*; Koizumi, Mitsuo; et al.

Nature Communications (Internet), 15, p.5365_1 - 5365_7, 2024/07

https://doi.org/10.1038/s41467-024-49142-y

Differential pressure rise event for filters of HTTR primary helium gas circulators, 2; Investigation of filter deposits and recurrence prevention measures

Nemoto, Takahiro; Fujiwara, Yusuke; Arakawa, Ryoki; Choyama, Yuya; Nagasumi, Satoru; Hasegawa, Toshinari; Yokoyama, Keisuke; Watanabe, Masashi; Onishi, Takashi; Kawamoto, Taiki; et al.

JAEA-Technology 2024-003, 17 Pages, 2024/06

JAEA-Technology-2024-003.pdf:1.91MB

In order to investigate the cause of the increase in differential pressure in the primary helium circulator filter that occurred during the RS-14 cycle, a clogged filter was investigated. As a result of the investigation, deposits caused by silicone oil were confirmed on the surface of the filter element. These results revealed that the cause of filter clogging was silicone oil mixed into the primary system due to performance deterioration of the charcoal filter in the gas circulator of primary helium purification system. As a measure to prevent the recurrence of this event, in addition to the conventional management based on operating hours for replacing of charcoal filter in the gas circulator of primary helium purification system, we have established a new replacement plan for every three years.

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.

High sensitivity of a future search for effects of -odd/-odd interactions on the 0.75 eV -wave resonance in + forward transmission determined using a pulsed neutron beam

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

Physical Review C, 109(4), p.L041602_1 - L041602_4, 2024/04

https://doi.org/10.1103/PhysRevC.109.L041602