Assessment of probability of aircraft crashes for Nuclear Science Research Institute

Kamikawa, Yutaka; Suzuki, Makoto; Agake, Toshiki; Murakami, Takahiko; Morita, Yusuke; Shiina, Hidenori; Fukushima, Manabu; Hirane, Nobuhiko; Ouchi, Yasuhiro

JAEA-Technology 2023-030, 57 Pages, 2024/03

JAEA-Technology-2023-030.pdf:1.93MB

Owing to the publication of the latest data about aircraft crashes by Nuclear Regulation Authority (NRA), it was necessary to re-evaluate the probabilities of aircraft crashes for Nuclear Science Research Institute (NSRI). By using of the assessment method provided in "Regulatory Guide of the Assessment Standard for Probability of Airplane Crash on a Nuclear Power Reactor Facility", we re-evaluated the probabilities of aircraft crashes against the nuclear facilities in NSRI. As a result of the evaluations, the sum of the probabilities of aircraft crashes against Waste Treatment Facilities (maximum probability among all nuclear facilities in NSRI) is 5.6810 (times/(reactor year)) which is lower than 10 (times/(reactor year)) that is the assessment criterion whether aircraft crashes is considered to be "anticipated external human induced events" in design basis or not.

Survey of air dose rate distribution inside and outside of wooden houses in Fukushima Prefecture; Actual condition of dose reduction factor

Kim, M.; Malins, A.*; Machida, Masahiko; Yoshimura, Kazuya; Saito, Kimiaki; Yoshida, Hiroko*

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(4), p.156 - 169, 2023/11

https://doi.org/10.3327/taesj.J23.001

Dose reduction factor of a Japanese house is important information in the external exposure estimation of returning residents. In 2019, a total of 19 wooden houses were surveyed in Iitate Village and Namie Town using a gamma plotter that can continuously measure the air dose rate. In addition, the characteristics of the reduction factor were investigated from the measured air dose rate. In the vicinity of houses, uncontaminated areas exist underneath houses and, the ratio of paved surfaces such as asphalt roads is relatively high; furthermore, the pavement has a tendency for the radiation source to decay quickly. Therefore, the air dose rate near the house showed a relatively low value in common at all sites. Air dose rates above unpaved surfaces showed higher values and larger variations than those above paved surfaces within a radius of 50 m form the center of a house. The reduction factor was widely distributed even for one house, if the ratio of every air dose rate observed inside and outside the house is considered. It is suggested that a realistic reduction factor may not be obtained when the reduction factor is obtained based on the measured values at a small number of points that do not have the representativeness of the radiation field to be measured.

Development of new containment tents for rapid worker evacuation from the workspace in emergencies at plutonium fuel handling facilities

Shibanuma, Tomohiro; Hirano, Hiroshi*; Kimura, Yasuhisa; Aita, Takahiro; Yoshida, Masato; Nagai, Yuya; Kitamura, Akihiro

Hoken Butsuri (Internet), 58(2), p.91 - 98, 2023/08

https://doi.org/10.5453/jhps.58.91

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.

Development of numerical simulation method of natural convection around heated porous medium by using JUPITER

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.

Implication of E3 ligase RAD18 in UV-induced mutagenesis in human induced pluripotent stem cells and neuronal progenitor cells

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

https://doi.org/10.1093/jrr/rrac099

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2021 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2022-026, 152 Pages, 2023/01

JAEA-Technology-2022-026.pdf:20.14MB

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.

A Numerical simulation method to evaluate heat transfer of fuel debris in air cooling by JUPITER, 2; Validation of porous model for natural convective heat transfer

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

Simulation of the self-propagating hydrogen-air premixed flame in a closed-vessel by an open-source CFD code

Thwe Thwe, A.; Terada, Atsuhiko; Hino, Ryutaro; Nagaishi, Ryuji; Kadowaki, Satoshi

Journal of Nuclear Science and Technology, 59(5), p.573 - 579, 2022/05

https://doi.org/10.1080/00223131.2021.1990153

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.

Investigations on distribution of radioactive substances owing to the Fukushima Daiichi Nuclear Power Station Accident in the fiscal year 2020 (Contract research)

Group for Fukushima Mapping Project

JAEA-Technology 2021-025, 159 Pages, 2022/01

JAEA-Technology-2021-025.pdf:46.66MB

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.

HAIROWorldPlugin operation manual

Suzuki, Kenta; Abe, Fumiaki; Yashiro, Hiroshi; Kawabata, Kuniaki

JAEA-Testing 2020-009, 254 Pages, 2021/03

JAEA-Testing-2020-009.pdf:18.61MB

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.