Katengeza, E. W.*; Ochi, Kotaro; Sanada, Yukihisa; Iimoto, Takeshi*; Yoshinaga, Shinji*
Health Physics, 121(1), p.48 - 57, 2021/07
Special reconstruction and revitalization bases were designated in Fukushima's difficult-to-return zones by the Japanese government as targets of intensive decontamination to drastically lower air dose rates and enable residents to return. A pond amidst residences of one of these bases was targeted for decontamination and this study aimed at evaluating the effect and effectiveness of the decontamination by decontamination factor, air dose rate reduction factor, and the additional annual effective dose to residents. Air dose rates were measured in-situ with KURAMMA-II while soil core samples were collected and measured for radioactivity in the laboratory by gamma spectrometry. Lower decontamination factors were observed for more deeply distributed radiocesium soil profiles whereas areas covered with gravel demonstrated the largest reduction in air dose rates. Decontamination effectively lowered the radiocesium inventory and air dose rates by 51% and 37-91% respectively. Moreover, the additional annual effective dose to the public changed from 1.70.79 mSv to 1.20.57 mSv because of decontamination representing a dose aversion of 29%. These findings demonstrate how decontaminating ponds in residential areas can help to further lower the external exposure.
Hagiwara, Kenta*; Ochi, Kotaro; Koike, Yuya*
Radioisotopes, 70(4), p.227 - 237, 2021/05
Behavior of radioactive caesium in river water and sediment in Tama river was investigated during 2012-2016. Concentrations of radioactive caesium in river water and sediment were decreased with time exponentially. Concentrations of suspended radioactive caesium, and radioactive caesium in sediment temporarily increased when sediments were resuspended due to rain. On the other hand, dissolved radioactive caesium was not easily impacted by this factor. Sequential extraction, elemental and crystal phase analysis were performed on the sediments and examined the chemical state of radioactive caesium as well as the adsorption mechanism. Radioactive caesium in sediment was present in a stable chemical form, and there is possibility that radioactive caesium was incorpolated in biotite.
Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi
Radiation Physics and Chemistry, 179, p.109205_1 - 109205_11, 2021/02
In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with several dose rate levels around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr(Ce) detectors to assess the radioactive cesium deposition in the ground. The diverse levels of radioactivity of Cs were then distributed to six survey sites from 30 to 3000 kBq m in the measurement period of October 2018. A method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site.
Malins, A.; Ochi, Kotaro; Machida, Masahiko; Sanada, Yukihisa
Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.147 - 154, 2020/10
Sanada, Yukihisa; Ochi, Kotaro; Ishizaki, Azusa
JAEA-Research 2020-006, 60 Pages, 2020/07
At the accident of nuclear facilities, a prediction of the behavior of released radioactive plume is indispensable to make a decision on a refuge plan of inhabitants. Currently, prediction system which is based on atmospheric dispersion simulation has been implemented as a tool of the atomic energy disaster prevention. However, the direct measurement method of the radioactive plume has not existed. In this study, some component technologies were developed for the establishment of direct measurement methods of radioactive plume using unmanned aerial vehicle whose technological innovation is remarkable. In addition, the spray test using mock aerosol was conducted to obtaining the deposition rate to the airplane body. The algorism of making a flight plan was developed based on a prediction model of the radioactive plume. This report summarized the outcome of the last year of the three-year plan.
Katengeza, E. W.*; Sanada, Yukihisa; Yoshimura, Kazuya; Ochi, Kotaro; Iimoto, Takeshi*
Environmental Science; Processes & Impacts, 22(7), p.1566 - 1576, 2020/07
Miwa, Kazuji; Terasaka, Yuta; Ochi, Kotaro; Futemma, Akira; Sasaki, Miyuki; Hirouchi, Jun
Nihon Genshiryoku Gakkai-Shi ATOMO, 61(9), p.687 - 691, 2019/09
This report summarizes the contents of the session of the Health Physics and Environment Science Division, which was held in Atomic Energy Society of Japan 2019 Spring Meeting. In this session, six students and young researchers who engaged in the field of nuclear energy and radiation gave a lecture about health physics and environmental science research through their expertise. After the all presentations end, we took discussion time about the issues and future development in this field with all attendees. In this report, we summarized each lecture outline and discussion contents.
Sanada, Yukihisa; Nishizawa, Yukiyasu*; Ochi, Kotaro; Yuki, Yoichi*; Ishizaki, Azusa; Osada, Naoyuki*
JAEA-Research 2018-009, 48 Pages, 2019/01
At the accident of nuclear facilities, a prediction of the behavior of released radioactive plume is indispensable to make a decision on a refuge plan of inhabitants. Currently, prediction system which is based on atmospheric dispersion simulation has been implemented as a tool of the atomic energy disaster prevention. However, the direct measurement method of the radioactive plume has not existed. In this study, some component technologies were developed for the establishment of direct measurement methods of radioactive plume using unmanned aerial vehicle whose technological innovation is remarkable. In addition, the spray test using mock aerosol was conducted to obtaining the deposition rate to the airplane body. The algorism of making a flight plan was developed based on a prediction model of the radioactive plume. This report summarized the outcome of the second year of the three-year plan.
Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sanada, Yukihisa
Progress in Nuclear Science and Technology (Internet), 6, p.103 - 107, 2019/01
After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a large amount of radionuclides was spread out all over the world. In our previous study, we developed the aerial radiation monitoring technique using unmanned helicopter for investigating the dose rate derived deposited radionuclides over wide area. In addition, many monitoring techniques were developed for investigating the local distribution of radionuclides using unmanned aerial vehicle, handheld instrument and car within small area. Distinction of these methods depends on desirable position resolution of dose rate. However, the comparison method of the measurement result between different methods is not established. In this study, we attempted to evaluate the some methods of airborne and ground radiation measurement in same extended farm.
Sanada, Yukihisa; Urabe, Yoshimi*; Sasaki, Miyuki; Ochi, Kotaro; Torii, Tatsuo
Journal of Environmental Radioactivity, 192, p.417 - 425, 2018/12
Sanada, Yukihisa; Miyamoto, Kenji*; Ochi, Kotaro; Matsuzaki, Koji*; Ogawa, Toshihiro*; Senga, Yasuhiro*
Kaiyo Riko Gakkai-Shi, 24(2), p.9 - 18, 2018/12
Seven years passed since Fukushima Dai-ichi Nuclear Power Station accident which was caused large amount of radionuclide release to the sea. Elucidation of behavior mechanism of radiocesium in the seabed is required for restarting fishing industry. We developed radiation detection system using the unmanned surface vehicle for in-situ measurement of radiocesium concentration in seabed sediment. This system is able to automatically navigate to measurement point and obtain the radiation data on the bottom sediment. The detector was calibrated by comparing the actual sediment samples. The periodical measurement off-shore the Fukushima Prefecture was performed using developed this system. As these results, distribution of radiocesium concentration was changed due to oceanographic condition. However, radiocesium inventory was tendency to decrease according to radiocesium half-life in measurement area. This system is effective for elucidation of behavior mechanism of radiocesium because it can easily measure the radiocesium concentration in the bottom sediment.
Ochi, Kotaro; Urabe, Yoshimi*; Yamada, Tsutomu*; Sanada, Yukihisa
Analytical Chemistry, 90(18), p.10795 - 10802, 2018/09
After the Fukushima Daiichi Nuclear Power Station accident, the distributions of sediment-associated radiocesium have been investigated to evaluate the dispersion and accumulation of radiocesium in the reservoir field. To develop an analytical method for measuring the horizontal and vertical distributions of radiocesium on a wide scale, we obtained 253 -ray spectra using a NaI(Tl) scintillation detector at the bottom of 64 ponds in Fukushima during 2014-2016. The depth profile of sediment-associated radiocesium was found to be correlated with intensities of scattered and photo peaks. In parallel, core sediments were collected in same ponds to validate the estimates. Good agreement was observed between the results of in situ spectrometry and core sampling. These results indicated that our developed method would be a good approach for understanding the behavior of radiocesium and determining whether decontamination of reservoirs is required.
Fujii, Kengo*; Ochi, Kotaro; Obuchi, Atsushi*; Koike, Yuya*
Journal of Environmental Management, 217, p.157 - 163, 2018/07
After the Fukushima Daiichi-Nuclear Power Plant accident, environmental recovery was a major issue because a considerable amount of municipal solid waste incineration (MSWI) fly ash was highly contaminated with radioactive cesium. In this study, MSWI fly ash was sampled in Fukushima Prefecture, and the physicochemical properties of radioactive cesium in MSWI fly ash were evaluated by particle size classification and the Japanese leaching test No. 13 (JLT-13). The results obtained from the classification of fly ash indicated that the activity concentration of radioactive cesium and the content of the coexisting matter (i.e., chloride, potassium, and sylvite) temporarily change in response to the particle size of fly ash. X-ray diffraction results indicated that water-soluble radioactive cesium exists as CsCl because of the cooling process and that insoluble cesium is bound to the inner sphere of amorphous matter.
Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa
International Journal of Environmental Research and Public Health, 14(8), p.926_1 - 926_14, 2017/08
After the Fukushima Daiichi Nuclear Power Plant accident, the vertical distribution of radiocesium in soil has been investigated to better understand the behavior of radiocesium in the environment. The typical method used for measuring the vertical distribution of radiocesium is troublesome because it requires collection and measurement of the activity of soil samples. In this study, we established a method of estimating the vertical distribution of radiocesium by focusing on the characteristics of -ray spectra obtained via aerial radiation monitoring using an unmanned helicopter. In this method, the change in the ratio of direct rays to scattered rays at various depths in the soil was utilized to quantify the vertical distribution of radiocesium. The results show a positive correlation between the abovementioned and the actual vertical distributions of radiocesium measured in the soil samples.
Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sato, Tomohiko*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa
no journal, ,
A large amount of radiocesium (Cs & Cs) were released into the atmosphere as a result of 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. To estimate the impact of the accident to the environment, dose rate around FDNPP have been measured by MEXT. Dose rate nearby FDNPP, however, still stay high even though decontamination work was carried out, which means it is necessary to develop an effective decontamination method promptly. Information of depth profile of radiocesium in soil is required to realize it, though, most of measurement methods have trouble due to collection and measurement of soil samples. As we have developed the radiation measurement techniques using unmanned aerial vehicle to measure dose rate distribution over wide areas for years, we attempt to establish the estimation method of depth profile of radiocesium in soil based on characteristics of -ray spectra obtained by airborne radiation monitoring in this paper.
Ochi, Kotaro; Sasaki, Miyuki; Ishida, Mutsushi*; Sanada, Yukihisa
no journal, ,
In previous studies, our group have developed the airborne radiation measurement (ARM) technique. We mounted a radiation detector under an unmanned aerial vehicle to evaluate the deposition of Fukushima accident-derived radiocesium over wide area. In this study, we performed ARM with mounting a LaBr(Ce) detector under an unmanned helicopter. A rapid and simple estimation of depth profile of radiocesium in soil was developed on the basis of the relationship between spectra obtained via ARM and actual depth profile of radiocesium. Our goal is same to series 1 that we attempt to achieve the advancement of airborne radiation measurement technique.
Ichihashi, Jun*; Kasari, Mitsuki*; Ochi, Kotaro; Koike, Yuya*
no journal, ,
In this study, we sampled a core soil using a core sampler (0-30 cm) at Kawasaki. A sequential extraction procedure was used to characterize radiocesium in each layer of soil. We selected six sampling points in cosideration of the vegetation. Four soils were collected at 900 cm range area. Core sample (0-30 cm) was devided into 5 cm layer and put in U-8 container, respectively. From measurement results, the vertival distribuition of radiocesium in core soil was 2.5 Bq kg (0-5 cm), 22.3 Bq kg (5-10 cm), 3.4 Bq kg (10-15 cm), 0.3 Bq kg (15-20 cm), 0.8 Bq kg (20-25 cm), 1.0 Bq kg (25-30 cm). It is indicated that radiocesium penetrate to deeper layer at Kawasaki.
Malins, A.; Ochi, Kotaro; Nakasone, Takamasa*; Yamada, Tsutomu*; Machida, Masahiko; Kurikami, Hiroshi; Saito, Kimiaki; Sanada, Yukihisa
no journal, ,
Here we report PHITS Monte Carlo simulations of a LaBr(Ce) gamma spectroscopy system used in unmanned helicopter radiation surveys in Fukushima Prefecture. The simulated spectra were verified against measurements taken under controlled laboratory conditions. Simulations were used to characterize the peak-to-Compton method for estimating the vertical distribution of radiocesium in soil from airborne surveys.
Ochi, Kotaro; Malins, A.; Ishida, Mutsushi*; Yamada, Tsutomu*; Nakasone, Takamasa*; Sanada, Yukihisa
no journal, ,
no abstracts in English
Malins, A.; Ochi, Kotaro; Sanada, Yukihisa; Yamaguchi, Ichiro*; Sato, Tatsuhiko
no journal, ,