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Journal Articles

Development of an ${it in-situ}$ continuous air monitor for the measurement of highly radioactive alpha-emitting particulates ($$alpha$$-aerosols) under high humidity environment

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:34.54(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 $$alpha$$-radionuclides ($$alpha$$-aerosols) that pose significant health risk upon inhalation. In order to minimize the radiation exposure of workers with $$alpha$$-aerosols during the dismantling/decommissioning process at 1F, it is essential to monitor the concentration of $$alpha$$-aerosols at the point of initial generation, i.e. inside the primary containment vessels (PCV) of the damaged reactors. Toward this end, an ${it in situ}$ monitoring system for $$alpha$$-aerosols (${it in situ}$ 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 $$alpha$$-radiation, and (4) selective measurement of $$alpha$$-radiation even under high radiation background with $$beta$$/$$gamma$$-rays. IAAM is capable of selectively measuring $$alpha$$-aerosols with a concentration of 3.3 $$times$$ 10$$^{2}$$ Bq/cm$$^{3}$$ or higher without saturation under a high humid environment (100%-relative humidity) and under high background with $$beta$$/$$gamma$$-radiation (up to 100 mSv/h of $$gamma$$-radiation). These results demonstrate promising potential of IAAM to be utilized as a reliable monitoring system for $$alpha$$-aerosols during the dismantling of NFD, as well as the whole long-lasting decommissioning of 1F.

Journal Articles

Comprehensive exposure assessments from the viewpoint of health in a unique high natural background radiation area, Mamuju, Indonesia

Nugraha, E. D.*; Hosoda, Masahiro*; Kusdiana*; Untara*; Mellawati, J.*; Nurokhim*; Tamakuma, Yuki*; Ikram, A.*; Syaifudin, M.*; Yamada, Ryohei; et al.

Scientific Reports (Internet), 11(1), p.14578_1 - 14578_16, 2021/07

 Times Cited Count:17 Percentile:84.99(Multidisciplinary Sciences)

Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study.

Journal Articles

Discriminative measurement of absorbed dose rates in air from natural and artificial radionuclides in Namie Town, Fukushima Prefecture

Ogura, Koya*; Hosoda, Masahiro*; Tamakuma, Yuki*; Suzuki, Takahito*; Yamada, Ryohei; Negemi, Ryoju*; Tsujiguchi, Takakiyo*; Yamaguchi, Masaru*; Shiroma, Yoshitaka*; Iwaoka, Kazuki*; et al.

International Journal of Environmental Research and Public Health, 18(3), p.978_1 - 978_16, 2021/02

 Times Cited Count:3 Percentile:70.28(Environmental Sciences)

Journal Articles

A Unique high natural background radiation area; Dose assessment and perspectives

Hosoda, Masahiro*; Nugraha, E. D.*; Akata, Naofumi*; Yamada, Ryohei; Tamakuma, Yuki*; Sasaki, Michiya*; Kelleher, K.*; Yoshinaga, Shinji*; Suzuki, Takahito*; Rattanapongs, C. P.*; et al.

Science of the Total Environment, 750, p.142346_1 - 142346_11, 2021/01

 Times Cited Count:20 Percentile:87.03(Environmental Sciences)

The biological effects of low dose-rate radiation exposures on humans remains unknown. In fact, the Japanese nation still struggles with this issue after the Fukushima Dai-ichi Nuclear Power Plant accident. Recently, we have found a unique area in Indonesia where naturally high radiation levels are present, resulting in chronic low dose-rate radiation exposures. We aimed to estimate the comprehensive dose due to internal and external exposures at the particularly high natural radiation area, and to discuss the enhancement mechanism of radon. A car-borne survey was conducted to estimate the external doses from terrestrial radiation. Indoor radon measurements were made in 47 dwellings over three to five months, covering the two typical seasons, to estimate the internal doses. Atmospheric radon gases were simultaneously collected at several heights to evaluate the vertical distribution. The absorbed dose rates in air in the study area vary widely between 50 nGy h$$^{-1}$$ and 1109 nGy h$$^{-1}$$. Indoor radon concentrations ranged from 124 Bq m$$^{-3}$$ to 1015 Bq m$$^{-3}$$. That is, the indoor radon concentrations measured exceed the reference levels of 100 Bq m$$^{-3}$$ recommended by the World Health Organization. Furthermore, the outdoor radon concentrations measured were comparable to the high indoor radon concentrations. The annual effective dose due to external and internal exposures in the study area was estimated to be 27 mSv using the median values. It was found that many residents are receiving radiation exposure from natural radionuclides over the dose limit for occupational exposure to radiation workers. This enhanced outdoor radon concentration might be as a result of the stable atmospheric conditions generated at an exceptionally low altitude. Our findings suggest that this area provides a unique opportunity to conduct an epidemiological study related to health effects due to chronic low dose-rate radiation exposure.

Journal Articles

Impressions of the 53rd Annual Meeting of Japan Health Physics Society

Hirouchi, Jun; Tani, Kotaro*; Tamakuma, Yuki*; Nakasone, Shunya*; Koike, Hiromi*

Hoken Butsuri (Internet), 55(4), p.185 - 190, 2020/12

no abstracts in English

Journal Articles

Cesium concentrations in various environmental media at Namie, Fukushima

Heged$"u$s, M.*; Shiroma, Yoshitaka*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Suzuki, Takahito*; Tamakuma, Yuki*; Yamada, Ryohei; Tsujiguchi, Takakiyo*; Yamaguchi, Masaru*; Ogura, Koya*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 323(1), p.197 - 204, 2020/01

 Times Cited Count:3 Percentile:32.21(Chemistry, Analytical)

The radioactivity of cesium in the water and sediments of two major rivers was measured along with airborne radioactivity in Namie Town, after the recent partial lift on the evacuation order in 2017. The observed concentrations were up to 384 $$pm$$ 11 mBq/L for $$^{137}$$Cs in unfiltered water and 1.28 $$pm$$ 0.09 mBq/m$$^{3}$$ for $$^{137}$$Cs in air, while the sediment had a maximum of 44900 $$pm$$ 23.4 Bq/kg for $$^{137}$$Cs. The $$^{134}$$Cs/$$^{137}$$Cs ratios indicate the main origin of the cesium in the sediment to be Unit 1 in good agreement with previous reports on the accident.

Journal Articles

Comparative study on performance of various environmental radiation monitors

Tamakuma, Yuki*; Yamada, Ryohei; Suzuki, Takahito*; Kuroki, Tomohiro*; Saga, Rikiya*; Mizuno, Hiroyuki*; Sasaki, Hiroyuki*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Tokonami, Shinji*

Radiation Protection Dosimetry, 184(3-4), p.307 - 310, 2019/10

 Times Cited Count:1 Percentile:11.41(Environmental Sciences)

After the Fukushima Daiichi Nuclear Power Plant accident, the radiation dose for first responders was not evaluated accurately due to lack of the monitoring data. It has been important to evaluate a radiation dose for workers in emergency response at a nuclear accident. In this study, a new device which can evaluate both of external and internal exposure doses was developed and the performance of various environmental radiation monitors including commercially available monitors were tested and compared from the viewpoint of an environmental monitoring at emergency situation. Background counts of the monitors and the ambient dose equivalent rate were measured in Fukushima Prefecture. The detection limit for beta particles was evaluated by the method of ISO11929. The sensitivity for gamma-rays of the dust monitor using a ZnS(Ag) and a plastic scintillator was high, but that of the external exposure monitor using a silicon photodiode with CsI(Tl) crystal was relatively low. The detection limit ranged 190-280 Bq m$$^{-3}$$ at 100 $$mu$$Sv h$$^{-1}$$, exceeding the detection limit of 100 Bq m$$^{-3}$$ in the minimum requirement by the National Regulation Authority in Japan. Use of the shielding with lead is necessary to achieve the minimum requirement. These results indicate that the dust monitor using a ZnS(Ag) scintillator and a plastic scintillator is suitable for the external exposure monitor and the developed internal exposure monitor is for the internal exposure monitor at emergency situation among the evaluated monitors. In the future study, the counting efficiency, the relative uncertainty and the performance of the detection for alpha particles will be evaluated, and it will be considered which type of a monitor is suitable after taking the portability into account.

Journal Articles

A Portable radioactive plume monitor using a silicon photodiode

Tamakuma, Yuki*; Yamada, Ryohei; Iwaoka, Kazuki*; Hosoda, Masahiro*; Kuroki, Tomohiro*; Mizuno, Hiroyuki*; Yamada, Koji*; Furukawa, Masahide*; Tokonami, Shinji*

Perspectives in Science (Internet), 12, p.100414_1 - 100414_4, 2019/09

In this study, a portable radioactive plume monitor using a silicon photodiode was developed for the detection of a radioactive plume (e.g. $$^{131}$$I, $$^{134}$$Cs and $$^{137}$$Cs) in an emergency situation. It was found that the background count rate was proportional to ambient dose equivalent rate and the detection limit for the monitor at 20 $$mu$$Sv h$$^{-1}$$ as an ambient dose equivalent rate was evaluated to be 187 Bq m$$^{-3}$$ using the ISO11929 method. These results suggest that the detection limit for the system can be decreased effectively by lead shielding with optimized thickness.

Journal Articles

Evaluation of a surface collection efficiency and a stability of flow rate for the commercially available filters used for ambient radioactive aerosols

Tamakuma, Yuki*; Yamada, Ryohei; Iwaoka, Kazuki*; Hosoda, Masahiro*; Tokonami, Shinji*

Hoken Butsuri (Internet), 54(1), p.5 - 12, 2019/03

Airborne radioactivity measurements are necessary to know the contamination level and internal doses for residents after a nuclear accident. In addition, measurements of radon progenies in air, which are the risk factor of lung cancer, are also important to evaluate lung dose. In these measurements, a filter sampling is used to collect radioactive aerosols. However, it is well known that results of the measurement using a filter are strongly dependent on characteristics of the used filter. Selection of a suitable filter is important to achieve the high-resolution and long-term measurement. "Surface collection efficiency (SCE)" and "stability of air flow rate" were examined for six types of filter that are commercially available in Japan. In Japan, cellulose-glass fiber filter paper (HE-40T) is used for an environmental monitoring in Japan. In this study, it was found that the SCE of HE-40T was lower than that of mixed cellulose ester type membrane filter by Merck Millipore (DAWP02500). Attenuation ratio of flow rate for DAWP02500 was evaluated to be 2.9% which was lowest in six filters. The results suggest that the DAWP02500 is the most suitable for collecting radioactive aerosols for a long term.

Oral presentation

Development of direct-type alpha dust monitor for in-situ measurement of airborne concentration during fuel debris retrieval and decommissioning of nuclear fuel cycle facilities

Tsubota, Yoichi; Honda, Fumiya; Nakagawa, Takahiro; Kawasaki, Takashi; Ikeda, Atsushi; Tamakuma, Yuki*; Tokonami, Shinji*; Momose, Takumaro

no journal, , 

A large number of radioactive aerosols, especially alpha particles, are expected to be generated during fuel debris retrieval on Fukushima - Daiichi (1F) site and decommissioning of nuclear fuel cycle facilities. For conventional alpha dust monitor, 1-channel of silicon surface barrier detector (SSBD) is often used as a detector which has not so high limit of count rates. Moreover, since radioactive aerosol collected on a filter paper are measured by a detector, it is difficult to calculate an airborne concentration at the sampling site because a conventional dust monitor measures an integrated radioactivity on a filter paper. In this work, we developed a prototype of alpha dust monitor aiming at an in-situ measurement of high concentration airborne alpha particles. The efficiency for U$$_{3}$$O$$_{8}$$ checking source was 80.8%. For high count rate test using 3 MBq of $$^{241}$$Am checking source, 2.1 $$times$$ 10$$^{7}$$ cpm was achieved which was more than 10 times higher compared to an conventional alpha dust monitor using SSBD. For follow-up test to the airborne concentration of alpha particles using radon chamber, counting rate of prototype alpha dust monitor was smoothly followed with respect to the radon concentration in a radon chamber.

Oral presentation

Development of elemental technology for alpha-ray dust monitor for in-situ measurement of radioactive aerosol in dismantling and decommissioning

Tsubota, Yoichi; Honda, Fumiya; Nakagawa, Takahiro; Kawasaki, Takashi; Tamakuma, Yuki*; Tokonami, Shinji*; Momose, Takumaro

no journal, , 

A large number of radioactive aerosols, especially alpha particles, are expected to be generated during fuel debris retrieval on Fukushima - Daiichi (1F) site and decommissioning of nuclear fuel cycle facilities. In the case of conventional alpha dust monitor, silicon surface barrier detector (SSBD) is often used as a detector which has not so high limit of count rates. Moreover, SSBD is not suitable for high humidity environment. In this work, we developed a prototype of alpha dust monitor aiming at an in-situ measurement of high concentration of airborne alpha particles. Approx. 20M cpm of counting rate was achieved which was more than 10 times higher compared to a conventional alpha dust monitor using SSBD. For follow-up test, counting rate of prototype alpha dust monitor was smoothly followed with respect to the airborne concentration of alpha particles.

Oral presentation

Performance evaluation for the selection of a filter for atmospheric radioactivity measurements

Yamada, Ryohei; Hashimoto, Hiroki*; Tamakuma, Yuki*; Hosoda, Masahiro*; Tokonami, Shinji*

no journal, , 

no abstracts in English

Oral presentation

Identification of artificial radionuclides in radioactive aerosol monitor

Hashimoto, Hiroki*; Yamada, Ryohei; Yamaguchi, Kanna*; Sasaki, Koichi*; Tamakuma, Yuki*; Hosoda, Masahiro*; Akata, Naofumi*; Tokonami, Shinji*

no journal, , 

no abstracts in English

Oral presentation

Measurement of equilibrium factors in various environments

Hashimoto, Hiroki*; Tamakuma, Yuki*; Yamada, Ryohei; Hosoda, Masahiro*; Tokonami, Shinji*

no journal, , 

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

Improvement of alpha aerosol monitor for in-situ measurement of airborne radioactive concentration in decommissioning

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

no journal, , 

A large amount of radioactive aerosols are expected to be dispersed fuel during debris cutting during large-scale retrieval of fuel debris at the Fukushima Daiichi Nuclear Power Plant (1F) and dismantling of nuclear fuel attachments during decommissioning of nuclear fuel facilities. Particulates containing $$alpha$$-nuclides ($$alpha$$-aerosols) in particular have very high effective dose coefficients upon inhalation, therefore appropriate control and measurements are required. Conventional dust monitors using SSBD have difficulties with moisture resistance, noise resistance, and clogging of filter paper. We have designed and prototyped an $$alpha$$-aerosol monitor that directly measures $$alpha$$-rays from aerosols using a scintillator and a multi-channel photomultiplier tube after drying the aerosols by heating the flat channel inlet without using a collecting filter paper in order to realize monitoring near the point where highly concentrated $$alpha$$-aerosols are generated. In this presentation, we report on the results of basic performance evaluations, the change in particle size due to air drying, and the improvement of the power supply method of the detection unit for on-site implementation at 1F.

Oral presentation

Discrimination of artificial radionuclides in a radioactive aerosol monitor; Correlation method of $$^{214}$$Po-gross alpha counts

Yamada, Ryohei; Hashimoto, Hiroki*; Tamakuma, Yuki*; Omori, Yasutaka*; Hosoda, Masahiro*; Akata, Naofumi*; Uchiyama, Rei; Nakada, Akira; Endo, Michitaka*; Imajo, Yusuke*; et al.

no journal, , 

no abstracts in English

Oral presentation

Development of "in-situ" alpha-ray dust monitors for fuel debris dismantling and decommissioning

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

no journal, , 

Aerosol behavior differs greatly depending on the generation history and processing method of NFDs. Especially for aerosols containing alpha ray emitting nuclides (alpha aerosols), which have a large internal dose upon inhalation, confinement and monitoring in the PCV are important. JAEA has been developing instruments to measure alpha aerosols in the 1F-PCV. The In-situ Alpha Air Monitor (IAAM), which was designed and developed to measure alpha aerosols "in-situ" in the harsh environment of the 1F-PCV, operates in a high-humidity, high gamma ray environment and can measure alpha aerosol concentrations 30 times The IAAM operates in a high humidity, high gamma ray environment and has demonstrated alpha aerosol measurement performance of more than 30 times the expected concentration in the 1F-PCV.

Oral presentation

Design and development of an "in-situ" alpha air monitor for harsh environments

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

no journal, , 

no abstracts in English

19 (Records 1-19 displayed on this page)
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