Effect evaluation of partial termination of local sampling system in Hot Laboratory at Oarai Nuclear Engineering Institute; Airflow analysis on diffusion of radioactive material

Fukui, Makoto; Chizuwa, Shingo*; Kikuchi, Norihiro; Tanaka, Masaaki; Hashimoto, Makoto

JAEA-Review 2025-045, 42 Pages, 2025/12

JAEA-Review-2025-045.pdf:2.95MB

Hot laboratory (HL) at Oarai Nuclear Engineering Institute is a facility that conducts post-irradiation testing of fuel samples and reactor materials in hot cells. A set of local sampling system (LSS) is installed as a radiation control equipment to monitor the concentration of radioactive materials in the air in work environment. The LSS of HL equipped 23 sampling points, which are called as local sampling ends (LSE). It was recognized that air sampling had not operated at some of the LSE, and the concentration of radioactive materials in the air was not measured as prescribed. In this report, we evaluated the effect of partial termination of the LSS and the resulting increase in sampling intervals on the control of radioactive material concentrations in the air using airflow analysis assuming the diffusion of radioactive materials from hot cells in the controlled area of HL. The Service Area of the HL, where 10 LSEs were set in a wide area, was selected as an evaluation area. Airflow analysis including the diffusion of virtual contaminant particles was conducted on the evaluation area. Diffusion of virtual contaminants from hot cells and sampling of virtual contaminants at LSEs are simulated in the case of LSS in fully working and LSS with termination of 4 LSEs. The evaluation results showed that the effect of the partial termination of LSS and the resulting increase in sampling intervals on the control of the concentration of radioactive materials in the air are small.

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.

Annual report on the effluent control of low level liquid waste in Nuclear Fuel Cycle Engineering Laboratories FY2023

Kokubun, Yuji; Hosomi, Kenji; Seya, Natsumi; Nagaoka, Mika; Inoue, Kazumi; Koike, Yuko; Hasegawa, Ryo; Kubota, Tomohiro; Hirao, Moe; Iizawa, Shogo; et al.

JAEA-Review 2024-053, 116 Pages, 2025/03

JAEA-Review-2024-053.pdf:3.26MB

Based on the regulations (the safety regulation of Tokai Reprocessing Plant, the safety regulation of nuclear fuel material usage facilities, the radiation safety rule, the regulation about prevention from radiation hazards due to radioisotopes, which are related with the nuclear regulatory acts, the local agreement concerning with safety and environment conservation around nuclear facilities, the water pollution prevention act, and by law of Ibaraki Prefecture), the effluent control of liquid waste discharged from the Nuclear Fuel Cycle Engineering Laboratories of Japan Atomic Energy Agency has been performed. This report describes the effluent control results of the liquid waste in the fiscal year 2023. In this period, the concentrations and the quantities of the radioactivity in liquid waste discharged from the reprocessing plant, the plutonium fuel fabrication facilities, and the other nuclear fuel material usage facilities were much lower than the limits authorized by the above regulations.

First freezing experiments with a molten mixture of boron carbide and stainless steel in core disruptive accidents of sodium-cooled fast reactors

Emura, Yuki; Matsuba, Kenichi; Kikuchi, Shin; Yamano, Hidemasa

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 8 Pages, 2024/11

Multistep kinetics of the thermal dehydration/decomposition of metakaolin-based geopolymer paste

Shindo, Manami*; Ueoku, Aya*; Okamura, Wakana*; Kikuchi, Shin; Yamazaki, Atsushi*; Koga, Nobuyoshi*

Thermochimica Acta, 738, p.179801_1 - 179801_12, 2024/08

https://doi.org/10.1016/j.tca.2024.179801

Development of safety design technologies for sodium-cooled fast reactor coupled to thermal energy storage system with sodium-molten salt heat exchanger, 3; Reaction on sodium-nitrate molten salt

Kikuchi, Shin; Sato, Rika; Kondo, Toshiki; Umeda, Ryota; Yamano, Hidemasa

Dai-28-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2024/06

no abstracts in English

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.

Thermophysical properties of dense molten AlO determined by aerodynamic levitation

Sun, Y.*; Takatani, Tomoya*; Muta, Hiroaki*; Fujieda, Shun*; Kondo, Toshiki; Kikuchi, Shin; Kargl, F.*; Oishi, Yuji*

International Journal of Thermophysics, 45(1), p.11_1 - 11_19, 2024/01

https://doi.org/10.1007/s10765-023-03302-2

no abstracts in English

Development of safety design technologies for sodium-cooled fast reactor coupled to thermal energy storage system with sodium-molten salt heat exchanger; Project overview

Yamano, Hidemasa; Kurisaka, Kenichi; Takano, Kazuya; Kikuchi, Shin; Kondo, Toshiki; Umeda, Ryota; Shirakura, Shota*

Dai-27-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 5 Pages, 2023/09

This project studies investigation on safety design guideline and risk assessment technology for sodium-cooled fast reactor with the molten-salt heat storage system, development of evaluation method for heat transferring performance between sodium and molten-salt and improvement of the performance, and evaluation of chemical reaction characteristic between sodium and molten-salt and improvement of its safety. The project overview is presented in this report.

Thermophysical properties of molten (FeO)-(SiO) measured by aerodynamic levitation

Kondo, Toshiki; Toda, Taro*; Takeuchi, Junichi*; Kikuchi, Shin; Kargl, F.*; Muta, Hiroaki*; Oishi, Yuji*

High Temperatures-High Pressures, 52(3-4), p.307 - 321, 2023/06

https://doi.org/10.32908/hthp.v52.1405

In order to establish an evaluation method/numerical simulation for nuclear reactor safety under severe accidental conditions, it is necessary to obtain the physical properties, especially fluidity of the relevant molten materials at very high temperatures. In this study, thermophysical properties such as density and viscosity were obtained for (FeO)-(SiO), which is a representative composition in the early stage of severe accident. (FeO)-(SiO) is produced by the contact between the molten oxide of steel, which is the main component of the reactor, and SiO, which is the main component of concrete. As a result, the physical properties of the (FeO)-(SiO) mixture were almost the same as those of FeO obtained in previous studies, and it could be concluded that a small amount of SiO (about 5 mol.%) did not significantly affect the fluidity of FeO.