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Journal Articles

Design policy of pilot plant for accelerator-driven system

Nishihara, Kenji; Sugawara, Takanori; Fukushima, Masahiro; Iwamoto, Hiroki; Katano, Ryota; Abe, Takumi

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

A pilot plant for the accelerator-driven system is proposed as a scaled-down version of a lead-bismuth cooled ADS with 800 MW thermal output for transmutation of minor actinides. In this presentation, the design policy of the pilot plant is presented.

JAEA Reports

Trial analysis of chemical behavior in high-level radioactive liquid waste tank at accident of evaporation to dryness by boiling of reprocessing plant

Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi

JAEA-Research 2024-007, 24 Pages, 2024/08

JAEA-Research-2024-007.pdf:2.1MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. It has been observed experimentally that volatility of RuO$$_{4}$$ is suppressed by HNO$$_{2}$$ generated by HNO$$_{3}$$ radiolysis. The analysis of chemical reactions of NO$$_{x}$$ including HNO$$_{3}$$ and HNO$$_{2}$$ in the waste tank is essential to simulate of these phenomena. To resolve this issue, an analytical approach has been attempted to couple dynamically two computer codes SHAWED and SCHERN. The simulation of boiling behavior in the tank is conducted with SHAWED. SCHERN simulates chemical behaviors of HNO$$_{3}$$, HNO$$_{2}$$ and NO$$_{x}$$ in the tank. A programmatic coupling algorithm and a trial simulation of the accident are presented in this report.

Journal Articles

Development of a surrogate system of a plant dynamics simulation model and an abnormal situation identification system for nuclear power plants using deep neural networks

Seki, Akiyuki; Yoshikawa, Masanori; Nishinomiya, Ryota*; Okita, Shoichiro; Takaya, Shigeru; Yan, X.

Nuclear Technology, 210(6), p.1003 - 1014, 2024/06

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

Two types of deep neural network (DNN) systems have been constructed with the intent to assist safety operation of a nuclear power plant. One is a surrogate system (SS) that can estimate physical quantities of a nuclear power plant in a computational time of several orders less than a physical simulation model. The other is an abnormal situation identification system (ASIS) that can estimate the state of the disturbance causing an anomaly from physical quantities of a nuclear power plant. Both systems are trained and tested using data obtained from the analytical code for incore and plant dynamics (ACCORD), which reproduces the steady and dynamic behavior of the actual high Temperature engineering test reactor (HTTR) under various scenarios. The DNN models are built by adjusting, the main hyperparameters. Through these procedures, these systems are shown able to perform with a high degree of accuracy.

Journal Articles

Estimating the corrosion rate of stainless steel R-SUS304ULC in nitric acid media under concentrating operation

Irisawa, Eriko; Kato, Chiaki

Journal of Nuclear Materials, 591, p.154914_1 - 154914_10, 2024/04

 Times Cited Count:2 Percentile:90.90(Materials Science, Multidisciplinary)

The amount of corrosion of austenitic stainless-steel R-SUS304ULC was evaluated considering the changes in solution composition and boiling during actual concentration operations. Austenitic stainless-steel R-SUS304ULC is the structural material of the highly radioactive liquid waste concentrator in Japanese spent fuel reprocessing plant, which treats highly corrosive nitric acid solutions during enrichment operations. The study results show that it is necessary to focus on nitric acid concentrations, oxidizing metal ion concentrations, and decompression boiling as factors that accelerate the corrosion rate of stainless steel because of cathodic reaction activation.

Journal Articles

Report on the lecture of standard committee in the 2023 fall meeting entitled "Standardization Activities for Safe Long Term Operation"

Murakami, Kenta*; Onizawa, Kunio; Yamamoto, Akio*

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 66(4), p.199 - 202, 2024/04

The Standards Committee of Atomic Energy Society of Japan has been leading activities related to long-term operation through the revision of the Code of Practice for Aging Management, and we believe that we must continue to make important contributions in light of recent changes in laws and regulations. This paper recapitulates the discussions in the special session conducted at the 2023 fall meeting, and describes the efforts toward safe long-term operation and the points to keep in mind in the standardization of such activities. The important points are (1) to make effective use of knowledge found over time, (2) not to overlook new knowledge that has a significant impact on safety, including obsolescence, (3) to assign a level of importance to the response based on the impact on safety and the likelihood of its occurrence, and (4) to contribute to the establishment of an international knowledge base.

Journal Articles

Resilient design in nuclear energy; Critical lessons from a cross-disciplinary analysis of the Fukushima Dai-ichi Nuclear accident

Ayoub, A.*; Wainwright, Haruko*; Sansavini, G.*; Gauntt, R.*; Saito, Kimiaki

iScience (Internet), 27(4), p.109485_1 - 109485_15, 2024/04

 Times Cited Count:4 Percentile:78.89(Multidisciplinary Sciences)

Journal Articles

Progress status and future issues of development of analysis and estimation technology for fuel debris characterization, 3; Activities toward enhanced analysis accuracy of fuel debris

Ikeuchi, Hirotomo; Koyama, Shinichi

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 66(2), p.74 - 78, 2024/02

For the steady removal of fuel debris from the TEPCO's Fukushima Daiichi Nuclear Power Station (1F), it is an urgent issue to establish analysis technology and systems for fuel debris samples with unknown properties (unknown samples). For this purpose, through analysis tests using samples with known properties (simulated fuel debris) and discussions among experts, the validity of analysis results and the factors that cause errors has been identified. In addition to knowing the current level of analysis accuracy, studies are being conducted to understand and improve the influencing factors. This paper introduces a part of the development of infrastructure for analysis and evaluation technology of "nuclides and element content."

Journal Articles

Neutronics-thermal-hydraulics-coupled transient analysis for reactor power change in an inclined offshore floating boiling water reactor

Fukuda, Kodai; Obara, Toru*; Suyama, Kenya

Nuclear Technology, 11 Pages, 2024/00

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

Journal Articles

Criticality safety evaluation of high active liquid waste during the evaporation to dryness process at Tokai Reprocessing Plant

Miura, Takatomo; Kudo, Atsunari; Koyama, Daisuke; Obu, Tomoyuki; Samoto, Hirotaka

Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 10 Pages, 2023/10

Tokai Reprocessing Plant (TRP) had reprocessed 1,140 tons of spent fuel discharged from commercial reactors (BWR, PWR) and Advanced Thermal Reactor "Fugen" from 1977 to 2007. TRP had entered decommissioning stage in 2018. In order to reduce the risk of High Active Liquid Waste (HALW) held at the facility, the vitrification of HALW is given top priority. HALW generated from reprocessing of spent fuel contains not only fission products (FPs) but also trace amounts of uranium (U) and plutonium (Pu) within the liquid and insoluble residues (sludge). Under normal conditions, concentrations of U and Pu in HALW are very low so that it can not reach criticality. Since FPs with high neutron absorption effect coexists in HALW, even if the cooling function is lost due to serious accident and HALW evaporates to dryness, it is considered that criticality would not been reached. In order to confirm this estimation quantitatively, criticality safety evaluations were carried out for the increase of U and Pu concentrations by evaporation of HALW to the point of dryness. In this evaluation, infinite multiplication factors were calculated for each of solution system and sludge system of HALW with respect to the concentration change through evaporation to dryness. It is confirmed it could not reach criticality. The abundance ratios of U, Pu and FPs were set conservatively based on analytical data and ORIGEN calculation results. Multiplation factors for two-layer infinite slab model of solution and sludge systems of HALW were also calculated, and it was confirmed it could not reached criticality. In conclusion, the result was gaind that there could be no criticality even in the process through evaporation to dryness of HALW in TRP.

Journal Articles

Soil dust and bioaerosols as potential sources for resuspended $$^{137}$$Cs occurring near the Fukushima Dai-ichi Nuclear Power Plant

Ota, Masakazu; Takahara, Shogo; Yoshimura, Kazuya; Nagakubo, Azusa; Hirouchi, Jun; Hayashi, Naho; Abe, Tomohisa; Funaki, Hironori; Nagai, Haruyasu

Journal of Environmental Radioactivity, 264, p.107198_1 - 107198_15, 2023/08

 Times Cited Count:0 Percentile:0.00(Environmental Sciences)

One of the current major radiation exposure pathways from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident-fallout is inhalation of the re-suspended $$^{137}$$Cs occurring in air. While wind-induced soil particle resuspension has been recognized as a primary mechanism of $$^{137}$$Cs resuspension, studies following the FDNPP accident suggested that fungal spores can be a significant source of the atmospheric $$^{137}$$Cs particularly in the rural areas such as difficult-to-return zone (DRZ). To elucidate the relative importance of the two resuspension phenomena, we propose a model simulating resuspension of $$^{137}$$Cs as soil particles and fungal spores, and applied it to DRZ. Our model's calculation showed that soil particle resuspension was responsible for the surface-air $$^{137}$$Cs observed during winter-spring, but could not account for the higher $$^{137}$$Cs concentrations observed in summer-autumn. The higher concentrations in the summer-autumn were in general reproduced by implementing fungal spore $$^{137}$$Cs emission, that replenished low soil particle $$^{137}$$Cs resuspension in that period. According to our model's concept, $$^{137}$$Cs accumulation in fungal spores and high spore emission rate characterized by the rural environment were likely responsible for the abundance of spore $$^{137}$$Cs in the air. It was inferred that the influence of the fungal spores on the atmospheric $$^{137}$$Cs would last longer since un-decontaminated forests still exist in DRZ.

Journal Articles

Occurrence of radioactive cesium-rich micro-particles (CsMPs) in a school building located 2.8 km south-west of the Fukushima Daiichi Nuclear Power Plant

Fueda, Kazuki*; Komiya, Tatsuki*; Minomo, Kenta*; Horie, Kenji*; Takehara, Mami*; Yamasaki, Shinya*; Shiotsu, Hiroyuki; Onuki, Toshihiko*; Grambow, B.*; Law, G. T. W.*; et al.

Chemosphere, 328, p.138566_1 - 138566_12, 2023/07

 Times Cited Count:4 Percentile:31.19(Environmental Sciences)

Journal Articles

Establishing an evaluation method for the aging phenomenon by physical force in fuel debris

Suzuki, Seiya; Arai, Yoichi; Okamura, Nobuo; Watanabe, Masayuki

Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07

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

The fuel debris, consisting of nuclear fuel materials and reactor structural materials, generated in the accident of Fukushima Daiichi Nuclear Power Plant can become deteriorated like rocks under the changes of environmental temperature. Although the fuel debris have been cooled by water for 10 years, they are affected by seasonal and/or day-and-night temperature changes. Therefore, in evaluating the aging behavior of the fuel debris, it is essential to consider the changes in environmental temperature. Assuming that the fuel debris are deteriorated, radioactive substances that have recently undergone micronization could be eluted into the cooling water, and such condition may affect defueling methods. We focused on the effect of repeated changes in environmental temperature on the occurrence of cracks, and an accelerated test using simulated fuel debris was carried out. The length of the crack increases with increasing number of heat cycle; therefore, the fuel debris become brittle by stress caused by thermal expansion and contraction. In conclusion, it was confirmed that the mechanical deterioration of the fuel debris is similar to that of rocks or minerals, and it became possible to predict changes in the length of the crack in the simulated fuel debris and environmental model.

Journal Articles

Accident sequence precursor analysis of an incident in a Japanese nuclear power plant based on dynamic probabilistic risk assessment

Kubo, Kotaro

Science and Technology of Nuclear Installations, 2023, p.7402217_1 - 7402217_12, 2023/06

 Times Cited Count:1 Percentile:34.39(Nuclear Science & Technology)

JAEA Reports

Development of analytical approach of source term for accident of evaporation to dryness by boiling of reprocessed high level liquid waste

Yoshida, Kazuo; Tamaki, Hitoshi; Hiyama, Mina*

JAEA-Research 2023-001, 26 Pages, 2023/05

JAEA-Research-2023-001.pdf:1.61MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. To resolve this issue, an analytical approach has been developed using computer simulation programs to assess the radioactive source term from those facilities. The proposed approach consists analyses with three computer programs. At first, the simulation of boiling behavior in the HLLW tank is conducted with SHAWED code. Next step, the thermal-hydraulic behavior in the facility building is simulated with MELCOR code based on the results at the first step simulation such as flowed out mixed steam flow rate, temperature and volatilized Ru from the tank. The final analysis step is carried out for estimating amount of released radioactive materials with SCHERN computer code which simulates chemical behaviors of nitric acid, nitrogen oxide and Ru based on the condition also simulated MELCOR. Series of sample simulations of the accident at a hypothetical typical facility are presented with the data transfer between those codes in this report.

Journal Articles

Aging of fuel-containing materials (fuel debris) in the Chornobyl (Chernobyl) Nuclear Power Plant and its implication for the decommissioning of the Fukushima Daiichi Nuclear Power Station

Kitagaki, Toru; Krasnov, V.*; Ikeda, Atsushi

Journal of Nuclear Materials, 576, p.154224_1 - 154224_14, 2023/04

 Times Cited Count:3 Percentile:46.34(Materials Science, Multidisciplinary)

Journal Articles

Applicability of differential die-away self-interrogation technique for quantification of spontaneous fission nuclides for fuel debris at Fukushima Daiichi Nuclear Power Plants

Nagatani, Taketeru; Sagara, Hiroshi*; Kosuge, Yoshihiro*; Nomi, Takayoshi; Okumura, Keisuke

Journal of Nuclear Science and Technology, 60(4), p.460 - 472, 2023/04

 Times Cited Count:1 Percentile:17.57(Nuclear Science & Technology)

Journal Articles

Attention-based time series analysis for data-driven anomaly detection in nuclear power plants

Dong, F.*; Chen, S.*; Demachi, Kazuyuki*; Yoshikawa, Masanori; Seki, Akiyuki; Takaya, Shigeru

Nuclear Engineering and Design, 404, p.112161_1 - 112161_15, 2023/04

 Times Cited Count:18 Percentile:99.18(Nuclear Science & Technology)

Journal Articles

Origin of Cs-bearing silicate glass microparticles observed during Fukushima accident and recommendations on nuclear safety

Hidaka, Akihide

Journal of Radioanalytical and Nuclear Chemistry, 332(6), p.1607 - 1623, 2023/03

 Times Cited Count:0 Percentile:0.00(Chemistry, Analytical)

no abstracts in English

Journal Articles

Mental health measures for the staff of nuclear research and development institution mobilized in dealing with residents during the nuclear disaster caused by the Great East Japan Earthquake

Tomotsune, Yusuke; Yajima, Mayumi; Okuno, Hiroshi; Yamamoto, Kazuya

Rodo Anzen Eisei Kenkyu, 16(1), p.29 - 43, 2023/02

During the first year of the accident at the Fukushima Daiichi Nuclear Power Station caused by the Great East Japan Earthquake in March 2011, a total of about 45,000 employees of Japan Atomic Energy Agency (JAEA) left their original workplaces to engage in telephone counseling, assistance of temporary return, and environmental monitoring. In particular, the staff who worked on the telephone counseling service, which directly contacted the residents, suffered from the stress associated with emotional labor. Systematic mental health care to the staff who engaged in these tasks was provided them in the Nuclear Fuel Cycle Engineering Laboratories of the JAEA. This paper considers this activity as a concrete example of "support for supporters" and discusses the mental health of the staff who provide support to the residents in a nuclear disaster.

JAEA Reports

Consideration on roles and relationship between observations/measurements and model predictions for environmental consequence assessments for nuclear facilities

Togawa, Orihiko; Okura, Takehisa; Kimura, Masanori

JAEA-Review 2022-049, 76 Pages, 2023/01

JAEA-Review-2022-049.pdf:3.74MB

Before construction and after operation of nuclear facilities, environmental consequence assessments are conducted for normal operation and an emergency. These assessments mainly aim at confirming safety for the public around the facilities and producing relief for them. Environmental consequence assessments are carried out using observations/ measurements by environmental monitoring and/or model predictions by calculation models, sometimes using either of which and at other times using both them, according to the situations and necessities. First, this report investigates methods, roles, merits/demerits and relationship between observations/measurements and model predictions which are used for environmental consequence assessments of nuclear facilities, especially holding up a spent nuclear fuel reprocessing plant at Rokkasho, Aomori as an example. Next, it explains representative examples of utilization of data on observations/measurements and results on model predictions, and considers points of attention at using them. Finally, the report describes future direction, for example, improvements of observations/measurements and model predictions, and fusion of both them.

332 (Records 1-20 displayed on this page)