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Shibanuma, Tomohiro; Hirano, Hiroshi*; Kimura, Yasuhisa; Aita, Takahiro; Yoshida, Masato; Nagai, Yuya; Kitamura, Akihiro
Hoken Butsuri (Internet), 58(2), p.91 - 98, 2023/08
We developed new containment tents that are more easily assembled and effectively functioned, by improving and refurbishing the shortcomings of the conventional tents. The new tents have been already tested in the real airborne contamination situation occurred at the plutonium fuel fabricating facility. The tents appropriately functioned for intended use but other shortcomings emerged and therefore we had modified the structure of the tents further.
Thwe Thwe, A.; Kadowaki, Satoshi; Nagaishi, Ryuji
Journal of Nuclear Science and Technology, 60(6), p.731 - 742, 2023/06
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)In this study, we performed numerical calculations of unsteady reaction flow considering detailed chemical reactions, investigated the unstable behavior of hydrogen-air dilute premixed flame due to intrinsic instability, and clarified the effects of unburned gas temperature and pressure. I made it. The unstable behavior of the flame in a wide space was simulated, and the burning rate of the cellular flame was obtained. Then, the effects of heat loss and flame scale on flame unstable behavior were investigated. The burning velocity of a planar flame increases as the unburned-gas temperature increases and it decreases as the unburned-gas pressure and heat loss increase. The normalized burning velocity increases when the pressure increases and heat loss becomes large, and it decreases when the temperature increases. This is because the high unburned-gas pressure and heat loss promote the unstable behavior and instability of flame.
Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05
For contaminated water management in decommissioning Fukushima Daiichi Nuclear Power Stations, reduction in water injection, intermittent injection water and air cooling are considered. However, since there are uncertainties of fuel debris in the PCV, it is necessary to examine and evaluate optimal cooling methods according to the distribution state of the fuel debris and the progress of the fuel debris retrieval work in advance. We have developed a method for estimating the thermal behavior in the air cooling, including the influence of the position, heat generation and the porosity of fuel debris. Since a large-scale thermal-hydraulics analysis of natural convection is necessary for the method, JUPITER developed independently by JAEA is used. It is however difficult to perform the large-scale thermal-hydraulics analysis with JUPITER by modeling the internal structure of the debris which may consist of a porous medium. Therefore, it is possible to analyze the heat transfer of the porous medium by adding porous models to JUPITER. In this study, we report the validation of JUPITER applied the porous model and discuss which heat transfer models are most effective in porous models such as series, parallel and geometric mean models. To obtain validation data of JUPITER for the natural convective heat transfer analysis around the porous medium, we performed the heat transfer and the flow visualization experiments of the natural convection in the experimental system including the porous medium. In the comparison between the experiment and the numerical analysis with each model, the numerical result with the geometric mean model was the closest of the models to the experimental results. However, the numerical results of the temperature and the velocity were overestimated for those experimental results. In particular, the temperature near the interface between the porous medium and air was more overestimated.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2022-062, 121 Pages, 2023/03
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2021, this report summarizes the research results of the "Study on water stopping, repair and stabilization of lower PCV by geopolymer, etc." conducted in FY2021. The present study aims to propose a construction method to stop jet deflectors by improved geopolymer and ultra-heavy muddy water, and to repair the lower part of the dry well. In addition, in order to increase the options for on-site construction in unknown situations such as deposition conditions, we will examine a wide range of construction outside the pedestal, and evaluate the feasibility of the construction method by the latest thermal flow simulation method. When widely constructed, fuel debris and deposits discharged out of the pedestal are coated with water stop and repair materials and become waste ...
Shimada, Mikio*; Tokumiya, Takumi*; Miyake, Tomoko*; Tsukada, Kaima*; Kanzaki, Norie; Yanagihara, Hiromi*; Kobayashi, Junya*; Matsumoto, Yoshihisa*
Journal of Radiation Research (Internet), 64(2), p.345 - 351, 2023/03
Times Cited Count:0 Percentile:0.01(Biology)Im, S.*; Jee, H.*; Suh, H.*; Kanematsu, Manabu*; Morooka, Satoshi; Choe, H.*; Nishio, Yuhei*; Machida, Akihiko*; Kim, J.*; Lim, S.*; et al.
Construction and Building Materials, 365, p.130034_1 - 130034_18, 2023/02
Times Cited Count:3 Percentile:93.65(Construction & Building Technology)Group for Fukushima Mapping Project
JAEA-Technology 2022-026, 152 Pages, 2023/01
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2021. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data to create air dose rate distribution maps, and temporal changes of the air dose rates were analyzed. Surveys on depth profile of radiocesium and in-situ measurements as for radiocesium deposition were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. Score maps to classify the importance of the measurement points were created for Fukushima Prefecture and the 80 km zone from the FDNPS, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. Monitoring data in coastal area performed owing to the comprehensive radiation monitoring plan until 2020 was summarized, and temporal changes in cesium-137 were analyzed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained in this project with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2021 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Kobayashi, Hikaru*; Suto, Masahito*; Otsuki, Kentaro*; Yoshimura, Kazuya; Yoshida, Hiroko*
Japan Architectural Review (Internet), 6(1), p.e12353_1 - e12353_12, 2023/00
Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 8 Pages, 2022/10
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2022-010, 155 Pages, 2022/06
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Development of the technology for preventing radioactive particles' dispersion during the fuel debris retrieval" conducted from FY2018 to FY2021 (this contract was extended to FY2021). Since the final year of this proposal was FY2021, the results for four fiscal years were summarized. The present study aims to clarify the behavior of microparticles in gas and liquid phases in order to steadily confine radioactive microparticles during fuel debris retrieval in Fukushima Daiichi Nuclear Power Station, TEPCO. As measures to prevent dispersion of microparticles, (1) a method to suppress the dispersion with minimum amount of water utilizing water spray etc., and (2) a method to suppress the dispersion by solidifying ...
Thwe Thwe, A.; Terada, Atsuhiko; Hino, Ryutaro; Nagaishi, Ryuji; Kadowaki, Satoshi
Journal of Nuclear Science and Technology, 59(5), p.573 - 579, 2022/05
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)The simulations of the combustion of self-propagating hydrogen-air premixed flame are performed by an open-source CFD code. The flame propagation behavior, flame radius, temperature and pressure are analyzed by varying the initial laminar flame speed and grid size. When the initial laminar speed increases, the thermal expansion effects become strong which leads the increase of flame radius along with the increase of flame surface area, flame temperature and pressure. A new laminar flame speed model derived previously from the results of experiment is also introduced to the code and the obtained flame radii are compared with those from the experiments. The formation of cellular flame fronts is captured by simulation and the cell separation on the flame surface vividly appears when the gird resolution becomes sufficiently higher. The propagation behavior of cellular flame front and the flame radius obtained from the simulations have the reasonable agreement with the previous experiments.
Tsubota, Yoichi; Honda, Fumiya; Tokonami, Shinji*; Tamakuma, Yuki*; Nakagawa, Takahiro; Ikeda, Atsushi
Nuclear Instruments and Methods in Physics Research A, 1030, p.166475_1 - 166475_7, 2022/05
Times Cited Count:1 Percentile:40.11(Instruments & Instrumentation)In the long-lasting decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), the dismantling of nuclear fuel debris (NFD) remaining in the damaged reactors is an unavoidable but significant issue with many technical difficulties. The dismantling is presumed to involve mechanical cutting, generating significant concentrations of particulates containing -radionuclides (
-aerosols) that pose significant health risk upon inhalation. In order to minimize the radiation exposure of workers with
-aerosols during the dismantling/decommissioning process at 1F, it is essential to monitor the concentration of
-aerosols at the point of initial generation, i.e. inside the primary containment vessels (PCV) of the damaged reactors. Toward this end, an
monitoring system for
-aerosols (
alpha air monitor: IAAM) was developed and its technical performance was investigated under the conditions expected for the actual environments at 1F. IAAM was confirmed to fulfill four technical requirements: (1) steady operation under high humidity, (2) operation without using filters, (3) capability of measuring a high counting rate of
-radiation, and (4) selective measurement of
-radiation even under high radiation background with
/
-rays. IAAM is capable of selectively measuring
-aerosols with a concentration of 3.3
10
Bq/cm
or higher without saturation under a high humid environment (100%-relative humidity) and under high background with
/
-radiation (up to 100 mSv/h of
-radiation). These results demonstrate promising potential of IAAM to be utilized as a reliable monitoring system for
-aerosols during the dismantling of NFD, as well as the whole long-lasting decommissioning of 1F.
Group for Fukushima Mapping Project
JAEA-Technology 2021-025, 159 Pages, 2022/01
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2020. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring for classifying the importance of measurement points, a score map was created for Fukushima Prefecture and the 80 km zone from the FDNPS, and the factors causing changes in the score when monitoring data from multiple years were used were discussed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2020 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Sanada, Yukihisa; Ishida, Mutsushi*; Yoshimura, Kazuya; Mikami, Satoshi
Journal of Radiation Protection and Research, 46(4), p.184 - 193, 2021/12
no abstracts in English
Suzuki, Kenta; Abe, Fumiaki; Yashiro, Hiroshi; Kawabata, Kuniaki
JAEA-Testing 2020-009, 254 Pages, 2021/03
This report is the user manual of HAIROWorldPlugin for Choreonoid. Our motivation is to develop a robot simulator based on Choreonoid for technological development to contribute the decommissioning work at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc. Choreonoid is an open source simulator which calculates the behavior of robots. The plugin is an extended function of Choreonoid which provides simulated behavior and phenomenon related to decommissioning tasks utilizing remotely operated robots. In particular, we developed additional functionalities for simulating the behavior of an underwater swimming robot, the behavior of an unmanned aerial vehicle robot, low visibility camera images, network communication failures, etc., and packaged these in the plugin. This report describes the installation of the plugin to Choreonoid on Ubuntu18.04-LTS and parameter settings of the plugin by presenting snapshots of operation windows.
Kitamura, Akira; Yoshida, Yasushi*
Journal of Radioanalytical and Nuclear Chemistry, 327(2), p.839 - 845, 2021/02
Times Cited Count:3 Percentile:51.72(Chemistry, Analytical)Thermodynamic data for radium for radioactive waste management have been predicted using an electrostatic model and correlation with the ionic radii of the alkaline earth metals. Estimation of the standard Gibbs free energy of formation and standard molar entropy of aqueous radium species and compounds has been based on such approaches as extrapolation of the thermodynamic properties of strontium and barium, and use of a model of ion pair formation. The predicted thermodynamic data for radium have been compared with previously reported values.
Katsumi, Toshiyuki; Yoshida, Yasuhito*; Nakagawa, Ryo*; Yazawa, Shinya*; Kumada, Masashi*; Sato, Daisuke*; Thwe Thwe, A.; Chaumeix, N.*; Kadowaki, Satoshi
Journal of Thermal Science and Technology (Internet), 16(2), p.21-00044_1 - 21-00044_13, 2021/00
Times Cited Count:3 Percentile:27.26(Thermodynamics)The effects of addition of CO and water vapor on characteristics of dynamic behavior of hydrogen/air premixed flames were elucidated experimentally. By Schlieren photography, wrinkles on the flame surface were clearly observed in low equivalence ratios. The propagation velocity increased monotonically as the flame radius became larger and flame acceleration was found. Increasing the addition of inert gas, the propagation velocity decreased, especially in the case of CO
addition. Moreover, the Markstein length and the wrinkling factor decreased. This indicated that the addition of Co
or H
O promoted the unstable motion of hydrogen flames, which could be due to the enhancement of the diffusive-thermal effect. Based on the characteristics of dynamic behavior of hydrogen flames, the parameters used in the mathematical model on propagation velocity including flame acceleration was obtained, and then the flame propagation velocity under various conditions was predicted.
Group for Fukushima Mapping Project
JAEA-Technology 2020-014, 158 Pages, 2020/12
This report presents results of the investigations on the distribution-mapping project of radioactive substances owing to TEPCO Fukushima Daiichi Nuclear Power Station (FDNPS) conducted in FY2019. Car-borne surveys, a flat ground measurement using survey meters, a walk survey and an unmanned helicopter survey were carried out to obtain air dose rate data. Air dose rate distribution maps were created and temporal changes of the air dose rates were analyzed. Regarding radiocesium deposition into the ground, surveys on depth profile of radiocesium and in-situ measurements were performed. Based on these measurement results, effective half-lives of the temporal changes in the air dose rates and the deposition were evaluated. In the examination of scoring to classify the importance of measurement points, we created a score map of Fukushima Prefecture and that within 80 km from the FDNPS based on the "score" method developed in 2018. The way of monitoring radioactive materials in land area was examined and the representativeness of monitoring points was proposed. Using the Bayesian hierarchical modeling approach, we obtained maps that integrated the air dose rate distribution data obtained from aircraft monitoring, car-borne surveys, and walk surveys with respect to the region within 80 km from the FDNPS and Fukushima Prefecture. The measurement results for FY2019 were published on the "Expansion Site of Distribution Map of Radiation Dose", and measurement data were stored as CSV format. Radiation monitoring and analysis of environmental samples owing to the comprehensive radiation monitoring plan were carried out.
Ando, Masaki; Sasaki, Miyuki; Saito, Kimiaki
Journal of Nuclear Science and Technology, 57(12), p.1319 - 1330, 2020/12
Times Cited Count:4 Percentile:48.93(Nuclear Science & Technology)Air dose rates measured by car-borne surveys within 80 km range of Fukushima Dai-ichi Nuclear Power Plant using KURAMA systems from 2011 up to 2018 were analyzed, and decreasing trends and ecological half-life were evaluated. The decreasing speed of air dose rates became 0.08 over a period of seven years, indicating a much more rapid decrease than estimated by the physical decay of radiocesium (0.3). The fast components of the ecological half-lives evaluated in entire the evacuation order area were about 2 to 3 y, and were considerably larger than those outside the evacuation order area (0.4 to 0.5 y). To model the acceleration in the decrease of air dose rates observed in evacuation order areas, we modified the bi-exponential curve formula of ecological half-life and introduced the two-group model. The fast decreasing components of the ecological half-life evaluated using the two-group model after 2013 were 0.5 to 1 y, and were much shorter than those up to 2013, at 2 to 3 y.
Ono, Masato; Hanawa, Yoshio; Sonobe, Hiroshi; Nishimura, Arashi; Sugaya, Naoto; Iigaki, Kazuhiko
JAEA-Technology 2020-010, 14 Pages, 2020/09
In response to new standard for regulating research and test reactor which is enforced December 18, 2013, it was carried out assessment of the probability of aircraft crashing for HTTR. According to assessment method provided in the Assessment Criteria of the Probability of Aircraft Crashing on Commercial Power Reactor Facilities, assessment was conducted targeting reactor building, spent fuel storage building and cooling tower. As a result, it was confirmed that the probability was 5.9810
, which is lower than the assessment criteria 10
.