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Journal Articles

Nacre-like MXene/polyacrylic acid layer-by-layer multilayers as hydrogen gas barriers

Auh, Y. H.*; Neal, N. N.*; Arole, K.*; Regis, N. A.*; Nguyen, T.*; Ogawa, Shuichi*; Tsuda, Yasutaka; Yoshigoe, Akitaka; Radovic, M.*; Green, M. J.*; et al.

ACS Applied Materials & Interfaces, 17(21), p.31392 - 31402, 2025/05

JAEA Reports

Study on the evaluation method of radioactivity for dismantling wastes generated from test and research reactors using ORIGEN attached to SCALE6.2.4

Tomioka, Dai; Kochiyama, Mami; Ozone, Kenji; Nakata, Hisakazu; Sakai, Akihiro

JAEA-Technology 2024-023, 38 Pages, 2025/03

JAEA-Technology-2024-023.pdf:1.54MB

Japan Atomic Energy Agency is an implementing organization of near-surface disposal for low-level radioactive wastes generated from research, industrial and medical facilities in Japan. Information on the radioactivity concentration of these radioactive wastes is dispensable for the design and conformity assessment of the waste disposal facilities for the licensing application of the disposal project and its safety review. Radioactive Wastes Disposal Center has been improving the radioactivity evaluation procedure for the dismantling waste generated from the research reactors based on the activation calculation. In order to investigate the applicability of the ORIGEN code (included in SCALE6.2.4), which enables more accurate activation calculations using multigroup neutron spectra, we performed activation calculations with the ORIGEN-code and the ORIGEN-S code (included in SCALE6.0), which has been widely used in the past, for the dismantled wastes from the Rikkyo University Research Reactor, where radioactivity analysis data for the structural materials around the reactor core were compiled. As a result, the calculation time difference between ORIGEN and ORIGEN-S was small and the evaluated radioactivity concentrations of the former were in the range of 0.8-1.0 times those of the latter, which was in good agreement with those of radiochemical analysis in the range of 0.5-3.0 times. The applicability of ORIGEN was confirmed. In addition, activation calculations assuming trace elements in structural materials of nuclear reactor were performed with ORIGEN and ORIGEN-S and the results were compared. The causes of the large differences among 170 nuclides that are important for dose assessment in near-surface disposal were assessed each nuclide.

Journal Articles

Development of gas entrainment evaluation model based on distribution of pressure along vortex center line; Application to a gas entrainment experiment with traveling vortices in an open water channel flow?

Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Sakai, Takaaki*

Nuclear Engineering and Design, 432, p.113785_1 - 113785_16, 2025/02

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

Establishing an evaluation method for the gas entrainment (GE) of argon cover gas due to surface vortices is required in terms of safety design of sodium-cooled fast reactors. To modify the evaluation model in an in-house evaluation tool for GE, StreamViewer, a modified evaluation model on the pressure distribution along the vortex center line (PVL model) was proposed to identify the vortex center lines by connecting continuous vortex center points from the suction port to the surface and evaluate gas core length based on the balance between the hydrostatic pressure and the pressure decrease distribution along the vortex center line. PVL model was applied the three-dimensional numerical analysis results for the experiments where a plate induced unsteady traveling vortices in the open channel flow. Consequently, the GE evaluation using StreamViewer with PVL model could reproduce the relation between the inlet flow velocity and the gas core length in the unsteady vortex flow experiments.

Journal Articles

Analyses of stress intensity factor solutions for subsurface flaws in flat plates

Li, S.; Li, Y.; Lu, K.*; Lacroix, V.*; Dulieu, P.*

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 18 Pages, 2024/07

JAEA Reports

Study on the evaluation methodology of the radioactivity concentration in low-level radioactive concrete wastes generated from JPDR

Aono, Ryuji; Haraga, Tomoko; Kameo, Yutaka

JAEA-Technology 2024-006, 48 Pages, 2024/06

JAEA-Technology-2024-006.pdf:1.77MB

In the future, radioactive waste which generated from nuclear research facilities in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. It is necessary to establish the method to evaluate the radioactivity concentrations of the radioactive wastes. In this work, we studied the evaluation methodology of the radioactivity concentrations in concrete waste generated from JPDR. In order to construct the evaluation methodology of the radioactivity concentration, the validity of the evaluation methods was confirmed by mainly theoretical calculation and using the result of radiochemical analysis. Correcting the theoretical calculations using results of nuclide analysis, it is possible to evaluate the radioactivity concentrations of nuclides preliminary selected.

JAEA Reports

Investigations and consideration on contamination inspection and decontamination criteria at a nuclear emergency

Togawa, Orihiko; Hokama, Tomonori; Hiraoka, Hirokazu; Saito, Shota

JAEA-Research 2023-011, 78 Pages, 2024/03

JAEA-Research-2023-011.pdf:2.09MB

When radionuclides are released into the atmospheric environment at a nuclear emergency, protective measures such as evacuation and temporal relocation are carried out using motor vehicles such as private cars and buses to reduce radiation exposure to residents. To confirm conditions of contamination for the evacuated/relocated residents and the used motor vehicles, contamination inspection is conducted in the middle of the route from border areas of Nuclear Emergency Planning Zone to evacuation shelters. In the present inspection in Japan, a value of OIL4 = 40,000 cpm is used as decontamination criteria. For the details and derivation methods of the value, however, no official documents are found which give systematically detailed descriptions and explanation. It is also recognized that even few experts on nuclear emergencies can explain these subjects in detail as a whole. In order to explain scientifically and technically the OIL4 value of decontamination criteria used in contamination inspection in Japan, this report aims at investigating and estimating the deviation methods of OIL4, and examining and considering these results. To achieve the objectives, we show the bases for decontamination criteria, and investigate and estimate the derivation methods for limits of a surface contamination density corresponding to the generic criteria for each exposure pathway. Moreover, we give the OIL4 value some consideration and suggestions from a viewpoint of positioning and feature of OIL4 in Japan, and cautionary points at revising the value.

Journal Articles

Cohesive/Adhesive strengths of CsOH-chemisorbed SS304 surfaces

Li, N.*; Sun, Y.*; Nakajima, Kunihisa; Kurosaki, Ken*

Journal of Nuclear Science and Technology, 61(3), p.343 - 353, 2024/03

 Times Cited Count:1 Percentile:25.62(Nuclear Science & Technology)

During the Fukushima Daiichi nuclear power plant (1F) accident, an overwhelming amount of the cesium remaining in the pressure vessel could have been deposited onto 304 stainless steel (SS304) steam separators and dryers, both with large surface areas. During 1F's decommissioning, the deposited cesium is a safety hazard as it can generate radioactive dust. However, the cohesive and adhesive strengths of CsOH-chemisorbed oxide scales are yet to be defined. In this study, we investigated how CsOH-chemisorption affects the cohesive and adhesive strengths between oxide scales and SS304 substrates with a scratch tester. The scratch test results revealed that the cohesive strengths of the oxide scales decreased after CsOH-chemisorption, while adhesive failure could not be reached.

JAEA Reports

Preparation of waste standards; Annual report 2022

Project Promotion Department; Radioactive Wastes Disposal Center

JAEA-Review 2023-037, 162 Pages, 2024/02

JAEA-Review-2023-037.pdf:2.66MB

For near surface disposal of radioactive wastes generated from research, industrial and medical facilities, Japan Atomic Energy Agency has discussed methods for corresponding to the technical standards on confirmation related to waste disposal, etc. From FY2022, we have established Waste Standards Committee and interim Waste Acceptance Criteria, Waste Package Confirmation Procedure, etc. have been considered. In FY2022, Waste Package Confirmation Procedures of solidified liquid waste and cement filled waste and related standards were discussed. In addition, issues of preparation of Waste Package Confirmation Procedure and rational treatment method for decommissioning wastes were considered. This annual report summarizes the results of discussion in FY2022.

Journal Articles

A Predicted CRISPR-mediated symbiosis between uncultivated archaea

Esser, S. P.*; Rahlff, J.*; Zhao, W.*; Predl, M.*; Plewka, J.*; Sures, K.*; Wimmer, F.*; Lee, J.*; Adam, P. S.*; McGonigle, J.*; et al.

Nature Microbiology (Internet), 8(9), p.1619 - 1633, 2023/09

 Times Cited Count:7 Percentile:77.08(Microbiology)

Journal Articles

Circumstances of establishment of regulations for near surface disposal of radioactive waste generated from research facilities, etc.

Sakai, Akihiro

Dekomisshoningu Giho, (64), p.24 - 33, 2023/05

Japan Atomic Energy Agency (JAEA) has proceeded with the project of near surface disposal of radioactive waste generated from research facilities, etc. as the implementing body. On the other hand, Nuclear Regulation Authority (NRA) has established the safety regulations and standards for the operation of the disposal facilities. This report outlines the disposal project of JAEA and the development of the regulations and standards for the disposal by NRA.

Journal Articles

CFD-based analysis and experimental study on gas entrainment phenomenon due to free surface vortex

Song, K.*; Ito, Kei*; Ito, Daisuke*; Odaira, Naoya*; Saito, Yasushi*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 10 Pages, 2023/05

Gas entrainment (GE) phenomena caused by a free surface vortex may cause the disturbance in core power of sodium-cooled fast reactor (SFR). For this reason, the entrained gas flow rate by the GE should be evaluated accurately for the practical safety design of SFRs. In this study, for the purpose of examining the applicability of CFD for the accurate evaluation of GE phenomena, a CFD is applied to the simulation of the free surface vortex and accompanied GE phenomena in a cylindrical vessel with a suction pipe, and the CFD results and the experimental data of the GE are compared. As a result, the CFD and experiments show similar two-phase flow pattern inside the suction pipe, and the shape of the gas core at the free surface is also very similar. Therefore, it is confirmed that the CFD can predict the GE phenomena triggered by a free surface vortex properly and accurately within the acceptable error range.

Journal Articles

Status of technical development for near surface disposal of radioactive waste generated from research facilities, etc.

Sakai, Akihiro

Dai-33-Kai Genshiryoku Shisetsu Dekomisshoningu Gijutsu Koza Tekisuto, p.31 - 63, 2023/02

The Japan Atomic Energy Agency (JAEA) is promoting the project for concrete-vault disposal and landfill-type disposal of radioactive waste generated from research facilities, etc. This report introduces current status of technical development for JAEA's disposal project as following items; (1) kinds of research facilities and characteristics of radioactivity inventory of the waste, (2) the structures of the disposal facilities which JAEA conceptually designed, (3) development of waste acceptance criteria for major radioactive waste for the JAEA disposal facilities, (4) the concept of the criteria for disposal of uranium bearing waste, that has been established in 2021.

Journal Articles

Free-surface flow simulations with floating objects using lattice Boltzmann method

Watanabe, Seiya*; Kawahara, Jun*; Aoki, Takayuki*; Sugihara, Kenta; Takase, Shinsuke*; Moriguchi, Shuji*; Hashimoto, Hirotada*

Engineering Applications of Computational Fluid Mechanics, 17(1), p.2211143_1 - 2211143_23, 2023/00

 Times Cited Count:10 Percentile:81.62(Engineering, Multidisciplinary)

In tsunami inundations or slope disasters of heavy rain, a lot of floating debris or driftwood logs are included in the flows. The damage to structures from solid body impacts is more severe than the damage from the water pressure. In order to study free-surface flows that include floating debris, developing a high-accurate simulation code of free-surface flows with high performance for large-scale computations is desired. We propose the single-phase free-surface flow model based on the cumulant lattice Boltzmann method coupled with a particle-based rigid body simulation. The discrete element method calculates the contact interaction between solids. An octree-based AMR (Adaptive Mesh Refinement) method is introduced to improve computational accuracy and time-to-solution. High-resolution grids are assigned near the free surfaces and solid boundaries. We conducted two kinds of tsunami flow experiments in the 15 and 70 m water tanks at Hachinohe Institute of Technology and Kobe University to validate the accuracy of the proposed model. The simulation results have shown good agreement with the experiments for the drifting speed, the number of trapped wood pieces, and the stacked angles.

Journal Articles

Characteristic Fermi surface properties in $$f$$-electron systems

Onuki, Yoshichika*; Settai, Rikio*; Haga, Yoshinori; Takeuchi, Tetsuya*; Hedo, Masato*; Nakama, Takao*

Quantum Science; The Frontier of Physics and Chemistry, p.21 - 63, 2022/10

Journal Articles

Development of the simplified boiling model applied for the large scale simulation by the detailed two-phase flow analysis based on the surface tracking

Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki

Dai-26-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2022/07

JAEA is implementing a simulation of a two-phase flow in the reactor core by TPFIT and JUPITER which are developed by JAEA based on the surface tracking method. However, it is impossible to simulate a boiling on the heating surface in the large-scale domain by this type of simulation method since the simulation of boiling based on the surface tracking method needs the fine mesh which sufficiently resolves the initiation of boiling. Therefore, JAEA started to develop the simplified boiling model applied for the two-phase flow in the fuel assemblies. In this study, the simulation results of the convection boiling on a vertical heating surface and the comparison between the simulation results and experimental results are shown.

Journal Articles

Split Fermi surface properties of noncentrosymmetric compounds Fe$$_2$$P, Ni$$_2$$P, and Pd$$_2$$Si

Onuki, Yoshichika*; Nakamura, Ai*; Aoki, Dai*; Matsuda, Tatsuma*; Haga, Yoshinori; Harima, Hisatomo*; Takeuchi, Tetsuya*; Kaneko, Yoshio*

Journal of the Physical Society of Japan, 91(6), p.064712_1 - 064712_10, 2022/06

 Times Cited Count:2 Percentile:28.67(Physics, Multidisciplinary)

Journal Articles

Contamination processes of tree components in Japanese forest ecosystems affected by the Fukushima Daiichi Nuclear Power Plant accident $$^{137}$$Cs fallout

Ota, Masakazu; Koarashi, Jun

Science of the Total Environment, 816, p.151587_1 - 151587_21, 2022/04

 Times Cited Count:8 Percentile:52.34(Environmental Sciences)

In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with $$^{137}$$Cs. However, $$^{137}$$Cs transfer processes determining tree contamination (particularly for stem wood, which is a prominent commercial resource in Fukushima) remain insufficiently understood. This study proposes a model for simulating the dynamic behavior of $$^{137}$$Cs in a forest tree-litter-soil system and applied it to two contaminated forests (cedar plantation and natural oak stand) in Fukushima. The model-calculated results and inter-comparison of the results with measurements elucidated the relative impact of distinct $$^{137}$$Cs transfer processes determining tree contamination. The transfer of $$^{137}$$Cs to trees occurred mostly ($$>$$ 99%) through surface uptake of $$^{137}$$Cs directly trapped by leaves or needles and bark during the fallout. By contrast, root uptake of $$^{137}$$Cs from the soil was unsubstantial and several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, the internal contamination of the trees proceeded through an enduring recycling (translocation) of $$^{137}$$Cs absorbed on the tree surface at the time of the accident. A significant surface uptake of $$^{137}$$Cs at the bark was identified, contributing 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining surface uptake occurred at the needles) of the total $$^{137}$$Cs uptake by trees. It was suggested that the trees growing at the study sites are currently (as of 2021) in a decontamination phase; the activity concentration of $$^{137}$$Cs in the stem wood decreases by 3% per year, mainly through radioactive decay of $$^{137}$$Cs and partly through a dilution effect from tree growth.

Journal Articles

Evaluation of gas entrainment flow rate by free surface vortex

Torikawa, Tomoaki*; Odaira, Naoya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki

Konsoryu, 36(1), p.63 - 69, 2022/03

On free surface of a sodium cooled fast reactor, gas entrainment can be caused by free surface vortices, which may result in disturbance in core power. It is important to develop an evaluation model to predict accurately entrained gas flow rate. In this study, entrained gas flow rate a simple gas entrainment experiment is conducted with focusing on effect of pressure difference between upper and lower tanks. Pressure difference between upper and lower tanks are controlled by changing gas pressure in lower tank. As a result, it is confirmed that the entrained gas flow rate increases with increasing pressure difference between upper and lower tanks. By visualization of swirling annular flow in suction pipe, it is also observed that pressure drop in suction pipe increases with increase in entrained gas flow rate, which implies that entrained gas flow rate can be predicted by evaluation model based on pressure drop in swirling annular flow region.

Journal Articles

Development of dose evaluation method considering radionuclides migration on the surface of the site for confirmation of completion of decommissioning

Miwa, Kazuji; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji

MRS Advances (Internet), 7(7-8), p.165 - 169, 2022/03

We have developed evaluation method of radiocesium (RCs) migration by surface runoff and soil erosion in considering vertical distribution of RCs in initial contaminated soil and concentration of RCs in different particle size. RCs migration on ground surface during single year has been evaluated in virtual site contaminated uniformly by Cs-137. As a result, RCs has concentrated in the impoundment, and 0.18% of total inventory in the site migrated into the sea. These results suggest that surface migration of RCs effects increasing of external exposure at impoundment and internal exposure from ingestion of marine product.

Journal Articles

Numerical simulation of two-phase flow in fuel assemblies with a spacer grid using a mechanistically based method

Ono, Ayako; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

JAEA is developing the methodology to predict the critical heat flux based on a mechanism in order to reduce the cost for full mock-up test. The evaluation method based on a mechanism is expected to be able to predict in the wide range of parameter under the unexpected conditions including the severe accident. In this study, the JUPITER code developed by JAEA is examined to apply for the two-phase flow simulation of LWR fuel assembly with the spacer grid. The benchmark data of single-phase flow in the bundle with the spacers by KAERI were used to validate the simulation result by JUPITER. Moreover, the single-phase flow simulation was conducted by another simulation method, STAR-CCM+, as a supplemental analysis to consider the effect of the different simulation methods. Finally, the two-phase flow simulation for the bundle with the spacer was conducted by JUPITER. The effect of the spacer with a vane on the bubble behavior is discussed.

343 (Records 1-20 displayed on this page)