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Oral presentation

Statistical evaluation of field of view in airborne radiation survey by comparison with the ground-based survey.

Sasaki, Miyuki; Sanada, Yukihisa

no journal, , 

In this study, we evaluated the field of view of airborne radiation survey which is obtained around the Fukushima Daiichi Nuclear Power Plant using the unmanned helicopter by comparison with a ground-based survey in the ambient dose rate. The field of view was evaluated from the convergence tendency of the error between airborne radiation survey value and ground-based measurement value. The convergence tendency of the error between the value of airborne radiation and the value of ground-based measurement was calculated by changing the mesh size. As a result, the field of view of airborne radiation survey at 50 m and 130 m altitudes were 100 m and 150 m mesh size respectively. These evaluation results are helpful for understanding the contour map of airborne radiation surveys. In addition, it is useful for the decision of flight conditions.

Oral presentation

Development of an alpha- and beta-imaging detector using a thin-stilbene plate for radon-222 progeny measurements

Morishita, Yuki

no journal, , 

Radon-222 ($$^{222}$$Rn) is a naturally-occurring radioactive gas, and the measurement of this isotope and its progeny is of interest from the viewpoint of protection against internal exposure. The author has developed a new alpha/beta-imaging detector combined with a waveform digitizer capable of imaging alpha- and beta-particle locations simultaneously. A 0.9-mm-thick stilbene plate was optically coupled to a position-sensitive photomultiplier tube (PSPMT), and the analog signals from the PSPMT were transferred in parallel to the waveform digitizer. For 5.5-MeV alpha particles, the detection efficiency was 97.2% for 2$$pi$$ steradians, and the energy resolution of the 5.5 MeV alpha peak was 21.6% full width at half maximum (FWHM). The imaging detector was able to discriminate between alpha and beta particles via the pulse-shape-discrimination (PSD) technique, as well as being capable of alpha- and beta-particle imaging. The imaging detector was used for $$^{222}$$Rn-progeny measurements. When measuring the $$^{222}$$Rn progeny, both $$^{214}$$Bi and $$^{214}$$Po are imaged simultaneously, and a correlation is found between the positions of $$^{214}$$Bi and $$^{214}$$Po. The developed detector will be useful as a $$^{222}$$Rn detector and in alpha-continuous-air monitoring for nuclear facilities.

Oral presentation

Oral presentation

Evaluation of analysis of airborne radiation survey using artificial neural network

Sasaki, Miyuki; Sanada, Yukihisa

no journal, , 

After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011, an airborne radiation survey (ARS) was conducted in Japan using a helicopter and unmanned aerial vehicle (UAV). ARS can quickly measure and collect data over wide areas. The position resolution of the source intensity by ARS is known to be rough compared with a ground-based survey because the detector position is far from a radiation source. We constructed and evaluated an artificial neural network (ANN). The ANN constructed to convert ARS data to the ambient dose equivalent rate (air dose rate) 1 m above ground level (AGL) to improve the measurement accuracy of ARS. In this study, we provide evaluation results of the conversion characteristic using the constructed ANN with ARS data acquired around FDNPP.

Oral presentation

A Study on corrosion potential of steel in RI dissolved solution

Aoyama, Takahito; Kato, Chiaki; Sato, Tomonori; Sano, Naruto; Yamashita, Naoki; Ueno, Fumiyoshi

no journal, , 

no abstracts in English

Oral presentation

Widespread diffusion of radioactive materials and deposition on the ground surface; Radiation monitoring immediately after the Fukushima Daiichi nuclear power plant accident and its fluctuations

Torii, Tatsuo*; Sanada, Yukihisa

no journal, , 

Ten years have passed since the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) caused by the Great East Japan Earthquake, and various efforts are being made in the field of radiation measurement. In an environment contaminated with radioactive material due to an accident, the contamination and air dose rate of radioactive material deposited on the ground surface can be monitored by various methods such as air, automobile, and human measurement. The Japan Atomic Energy Agency (JAEA) conducted an aerial radiation survey using a manned helicopter, and developed and established an analysis method at the same time as the development of this survey method. The reliability of the aerial radiation monitoring data was confirmed through comparison with a large amount of ground measurement data. In addition to the physical decay of radioactive cesium, the increased damping effect of the infiltration of radioactive cesium into the soil reduced the air dose rate. These results demonstrate the importance of aerial monitoring to assess and predict radiation exposure of residents.

Oral presentation

Preliminary study of isotopic ratio of $$^{135}$$Cs/$$^{133}$$Cs for micron sized particle by ToF-SIMS

Tagomori, Hisaya*; Kawamura, Hidehisa*; Kusano, keiichi*; Dohi, Terumi; Fujiwara, Kenso

no journal, , 

no abstracts in English

Oral presentation

Synergistic effect of aluminum lactate and sodium molybdate on freshwater corrosion inhibition of carbon steel

Otani, Kyohei; Ueno, Fumiyoshi; Kato, Chiaki

no journal, , 

In order to develop a novel corrosion inhibitor that is suitable for the 1F environment, it was focused on aluminum lactate, which had not been focused on as a corrosion inhibitor. It was found that aluminum lactate had a synergistic effect and high corrosion inhibition ability when mixed with sodium molybdate. As a result of surface XPS analysis, it was found that the corrosion of carbon steel was inhibited by the formation of aluminum and molybdenum oxide films on the carbon steel surface.

Oral presentation

Behavior of radionuclides in rivers in Fukushima

Nakanishi, Takahiro; Igarashi, Yasunori*

no journal, , 

no abstracts in English

Oral presentation

Oral presentation

An In-situ alpha air monitor for the retrieval of fuel debris at the Fukushima Daiichi Nuclear Power Station

Honda, Fumiya; Tsubota, Yoichi; Tamakuma, Yuki*; Tokonami, Shinji*; Ikeda, Atsushi; Nakagawa, Takahiro

no journal, , 

A large number of radioactive aerosols, especially alpha particles, are expected to be generated during the fuel debris retrieval on the Fukushima Daiichi Nuclear Power Station. From the viewpoint of preventing contamination of the surrounding environment and the vicinity of the human-access area, it is important to measure the activity concentration of airborne radioactive substances inside the primary containment vessels (PCVs). In particular, it is necessary to monitor the concentration of particulates containing $$alpha$$-nuclides ($$alpha$$-aerosols), which have high effective dose coefficients upon inhalation. This presentation reports the development of an in-situ alpha air monitor (IAAM) for direct measurement of $$alpha$$-aerosols by combining a flat-type flow path (FFP), an air heater, a ZnS scintillator, and a multi anode photomultiplier tube. The monitor should operate under high humidity with the maximum counting rate of approx. 2.1$$times$$10$$^{7}$$ cpm. To achieve the two requirements, the monitor was designed to keep the air sufficiently dry without overheating the detector, and to reduce the detection of coarse particles. This study also conducted a basic performance test using the developed IAAM with a modified FFP. As a result, we could keep the humidity of the air less than 30%RH by heating the inlet of the FFP to 80 $$^{circ}$$C. In addition, by placing the FFP in a vertical position and installing a bend at the air intake port, coarse particles were reduced approx. 1/2-1/3. These achievements enable the monitor to measure $$alpha$$-aerosols more precisely in the viewpoint of internal exposure assessment.

Oral presentation

Contribution of particulate $$^{137}$$Cs from rivers to $$^{137}$$Cs concentrations in coastal sediment off Fukushima

Suzuki, Shotaro*; Sakuma, Kazuyuki; Tsuruta, Tadahiko; Matsumoto, Akira*; Amano, Yosuke*; Enomoto, Masahiro*; Morioka, Yoshiaki*; Kamiyama, Kyoichi*; Takata, Hyoe*

no journal, , 

Oral presentation

Atmospheric transport and deposition of Fukushima-derived radionuclides

Hirao, Shigekazu*; Satou, Yukihiko

no journal, , 

Oral presentation

Two-dimensional elemental mapping of simulated fuel debris using laser induced breakdown spectroscopy

Batsaikhan, M.; Karino, Takahiro; Shibata, Takuya; Akaoka, Katsuaki; Wakaida, Ikuo

no journal, , 

Journal Articles

Formation of Type A glassy cesium-bearing microparticles from HEPA filter materials in Unit 3 during Fukushima Dai-ichi NPS accident; From viewpoint of similarity in silicate glass composition

Hidaka, Akihide

Proceedings of 2021 International Congress on Advances in Nuclear Power Plants (ICAPP 2021) (USB Flash Drive), 10 Pages, 2021/10

Author recently proposed that the Type A glassy Cesium-bearing microparticles that were released during the Fukushima accident may have been formed by melting and atomization of glass fibers of the High Efficiency Particulate Air (HEPA) filter in the Stand-by Gas Treatment System (SGTS) line in Unit 3 during the hydrogen explosion. In the present study, the components of the Type A and glass fibers of HEPA filter were examined using EPMA. The results showed that the components of the Type A were almost the same as that of the glass fibers except for Cs, Fe, Sn, which are considered to have been contained in the in-vessel-derived particles. When the glass fiber was irradiated with the electron beam of the Electron Probe Micro Analyzer (EPMA) under vacuum condition, spherical particles of a few micro m size were formed that looked very similar to the Type A. These strongly suggest that the HEPA filter is Si source of the Type A.

Journal Articles

Raman investigation of the CLADS-MADE-02 test debris to confirm the mechanism of the volatile and non-volatile boron compounds formation

Pshenichnikov, A.; Nagae, Yuji; Kurata, Masaki

Proceedings of TopFuel 2021 (Internet), 12 Pages, 2021/10

Oral presentation

Visualizing the dose rate distribution around the Fukushima Daiichi Nuclear Power Plant using artificial neural networks

Sasaki, Miyuki

no journal, , 

This study proposes a method of visualizing the ambient dose rate distribution using artificial neural networks (ANN) from airborne radiation monitoring results. The ANN method was applied to the results of the airborne radiation monitoring which was conducted around the Fukushima Daiichi Nuclear Power Plant by an unmanned aerial vehicle. The ANN was constructed by training data consisting of input variable dataset (radiation count rate, altitude, topographic data, photographic RGB data) and objective variable dataset (the air dose rate data at 1 m above the ground level). The reliability of the ANN method was evaluated by comparison with the ground-based survey data. The dose rate map created by the ANN method reproduced ground-based survey results better than traditional methods.

Oral presentation

Investigation on distribution of radioactive substances in Fukushima, 5; Decrease in air dose rate resulted by the radiocesium dynamics on paved and unpaved

Yoshimura, Kazuya; Fujiwara, Kenso; Nakama, Shigeo; Abe, Tomohisa

no journal, , 

no abstracts in English

4803 (Records 1-20 displayed on this page)