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Journal Articles

Post-test analyses of the CMMR-4 test

Yamashita, Takuya; Madokoro, Hiroshi; Sato, Ikken

Journal of Nuclear Engineering and Radiation Science, 8(2), p.021701_1 - 021701_13, 2022/04

Journal Articles

Joint environmental radiation survey by JAEA and KAERI around the Fukushima Daiichi Nuclear Power Plant; Performance of mobile gamma-ray spectrometry using backpack and carborne survey platforms

Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi

Health Physics, 121(6), p.613 - 620, 2021/12

According to the implementing arrangement between JAEA (Japan Atomic Energy Agency) and KAERI (Korea Atomic Energy Research Institute) in the field of the radiation protection and environmental radiation monitoring, the joint measurement has been conducted to assess the radioactive cesium deposition in the ground around the Fukushima Daiichi Nuclear Power Plants (FDNPP). First, mobile gamma-ray spectrometry using backpack survey platform was conducted to assess the distribution of dose rate around specific three survey sites. The carborne survey using gamma-ray spectrometers, as loading inside a vehicle, was successfully conducted to compare measured dose rates in routes from site to site and verify evaluation methods including the attenuation correction.

Journal Articles

Evaluation of the dissolution behavior of zircon using high-resolution phase-shift interferometry microscope

Kitagaki, Toru

Journal of Nuclear Materials, 557, p.153254_1 - 153254_8, 2021/12

 Times Cited Count:0

Journal Articles

High temperature reaction of multiple eutectic-component system; The Case of solid metallic Zr and molten stainless steel-B$$_{4}$$C

Sumita, Takehiro; Kobata, Masaaki; Takano, Masahide; Ikeda, Atsushi

Materialia, 20, p.101197_1 - 101197_11, 2021/12

JAEA Reports

Test methods for robots for nuclear emergency response and decommissioning; Tests for moving performances of robots (JAEA-TM-0004 and JAEA-TM-0005)

Kawabata, Kuniaki; Yamada, Taichi; Abe, Hiroyuki*

JAEA-Technology 2021-021, 30 Pages, 2021/11

JAEA-Technology-2021-021.pdf:2.55MB

This report describes the test procedures for performance evaluation of remotely operated robot utilized for nuclear emergency responses and decommissioning that provide to compare among the robot's performances quantitatively and relatively. After the accident at Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company Holdings Inc. (FDNPS) occurred, remotely operated robots have been deployed and utilized in the response tasks. Such post-accident work experiences and lessons learned are very valuable for developing the robots in the future. Therefore, we were motivated to develop the test methods for performance evaluation of the robot by referring with such experiences and lessons. In recent decommissioning tasks, reconnaissance on the distribution and status of nuclear fuel debris inside the Primary Containment Vessel (PCV) have been carried out. The insertion and deployment of robots into PCV were carried out through a penetration pipe with small diameter to prevent the scattering of radioactive materials. According to the authors' survey on such works have carried out in Units 1 and 2 of FDNPS, in order to carry out the reconnaissance work by the robot deployed into the PCV, it was clarified that the robots are required to run freely on the floor located below the exit of the penetration pipe and run freely on the inclined surface located below the exit of the pipe. This document describes two test procedures for performance evaluation of the robot connected with the cable such as running on the floor after being deployed through a penetration pipe and running on the inclined surface after being deployed through a penetration pipe. Typical course layout and the demonstration of test running are also illustrated for the references.

JAEA Reports

Background radiation monitoring using manned helicopter for application of technique of nuclear emergency response in the fiscal year 2020 (Contract research)

Futemma, Akira; Sanada, Yukihisa; Sasaki, Miyuki; Kawasaki, Yoshiharu*; Iwai, Takeyuki*; Hiraga, Shogo*; Sato, Kazuhiko*; Haginoya, Masashi*; Matsunaga, Yuki*; Kikuchi, Hikaru*; et al.

JAEA-Technology 2021-020, 138 Pages, 2021/11

JAEA-Technology-2021-020.pdf:17.11MB

A large amount of radioactive material was released by the nuclear disaster of Fukushima Daiichi Nuclear Power Station (FDNPS), Tokyo Electric Power Company, caused by the Great East Japan Earthquake and the following tsunami on March 11, 2011. After the nuclear disaster, airborne radiation monitoring via manned helicopter has been utilized to grasp rapidly and widely the distribution of the radioactive materials surrounding FDNPS. We prepare the data of background radiation dose, geomorphic characteristics and the controlled airspace surrounding nuclear facilities of the whole country in order to make effective use of the monitoring technique as a way of emergency radiation monitoring and supply the results during an accident of a facility. This report is summarized that the knowledge as noted above achieved by the aerial radiation monitoring around Tsuruga and Mihama nuclear power station, research reactors in Kindai University Atomic Energy Research Institute and Institute for Integrated Radiation and Nuclear Science, Kyoto University. In addition, examination's progress aimed at introduction of airborne radiation monitoring via unmanned plane during nuclear disaster and the technical issues are summarized in this report.

JAEA Reports

Semi-autonomous remote-control technology of an articulated mobile robot to recover from stuck states (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Electro-Communications*

JAEA-Review 2021-025, 33 Pages, 2021/11

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 FY2019, this report summarizes the research results of the "Semi- autonomous remote-control technology of an articulated mobile robot to recover from stuck states" conducted in FY2020. The purpose of this work is to establish a recovery method of an articulated mobile robot from stuck states. In this work, a control method of the robot to recover from stuck states by using redundancy of the system is proposed. In addition, we develop two interfaces. One is a display interface as an operator can understand the situation of the robot and surrounding terrain, and the other is a control interface to provide a target motion using the proposed control method. Finally, the effectiveness of them is demonstrated by experiments using an actual robot.

JAEA Reports

Survey on the radioactive substance in the coastal areas near Fukushima Prefecture in FY2020 (Contract research)

Misono, Toshiharu; Nakanishi, Takahiro; Sanada, Yukihisa; Shiribiki, Takehiko; Urabe, Yoshimi*; Tsuruta, Tadahiko

JAEA-Research 2021-004, 214 Pages, 2021/11

JAEA-Research-2021-004.pdf:12.76MB

After the accident of TEPCO's Fukushima Daiichi Nuclear Power Station (1F), the project of marine monitoring survey on radioactive substances have been conducted by the contract research from the Nuclear Regulatory Agency in FY2020. Results obtain in the project are presented in this report. Based on the monitoring results of radioactive substances of seawater and sediments, we suggested the evaluation method for optimizing the survey points and frequency, and examined the proper monitoring method on marine monitoring. In addition, core samples were collected at 70 points at the coast of Fukushima Prefecture to reveal the accumulation of radioactive Cs in the sediments. Furthermore, in order to evaluate the inflow of radioactive Cs from the river, sediment traps were installed at the coastal area to collect sinking sediment, and the horizontal distribution of the radioactive Cs concentration on the surface sediment in front of the rivers was measured. We carried out the revaluation of the towed radiation monitoring data conducted from 2013 to 2018, taking into account the natural radionuclides, and improved the radioactive Cs distribution map in the coastal sediments. In addition, a seabed topography and sediments distribution survey was conducted in the silt band area off the 1F to understand the topography and sediment distribution. From these results, we estimated the distribution and its dynamics of radioactive Cs in the sediments in the front area on the 1F.

Journal Articles

Spatial variations in radiocesium deposition and litter-soil distribution in a mountainous forest catchment affected by the Fukushima nuclear accident

Atarashi-Andoh, Mariko; Koarashi, Jun; Tsuzuki, Katsunori; Takeuchi, Erina; Nishimura, Shusaku; Muto, Kotomi*; Matsunaga, Takeshi*

Journal of Environmental Radioactivity, 238-239, p.106725_1 - 106725_8, 2021/11

To understand the spatial variation in soil $$^{137}$$Cs inventory in complex mountainous topography, a whole-area investigation of $$^{137}$$Cs deposition in a broad-leaved forest catchment of a mountain stream was conducted using grid sampling. Across the catchment, organic and surface mineral soil layers were collected at 42 locations in 2013 and 6 locations in 2015. $$^{137}$$Cs deposition on the forest floor exhibited high spatial heterogeneity and altitude-dependent distribution over the catchment. The $$^{137}$$Cs retention ratio in the organic layer ranged from 6% to 82% in 2013. The $$^{137}$$Cs retention ratios had positive correlations with the material inventory in the organic layer and the elevation. The $$^{137}$$Cs retention ratios in the organic layer were less than 20% in 2015, even at the locations where the retention ratio was higher than 55% in 2013. Although there was spatial variation in the migration speed, $$^{137}$$Cs migration from the organic layer to mineral soil was almost completed within 4 y of the deposition.

Journal Articles

Dynamics of radiocaesium within forests in Fukushima; Results and analysis of a model inter-comparison

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.

Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11

 Times Cited Count:0 Percentile:0(Environmental Sciences)

This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.

Journal Articles

A Modeling study on the oceanic dispersion and sedimentation of radionuclides off the coast of Fukushima

Kamidaira, Yuki; Uchiyama, Yusuke*; Kawamura, Hideyuki; Kobayashi, Takuya; Otosaka, Shigeyoshi*

Journal of Environmental Radioactivity, 238-239, p.106724_1 - 106724_16, 2021/11

 Times Cited Count:0 Percentile:0(Environmental Sciences)

A three-dimensional oceanic dispersion model considering the migration of radionuclides between seawater and sediments was developed. The migration mechanism of dissolved Cs-137 originating from the Fukushima Daiichi Nuclear Power Plant accident to sediments was investigated. The comparison between the model and the observed data showed that the model can adequately reproduce the ocean structure and the concentration of Cs-137 in seawater and sediments. Cs-137 distribution in the sediment off the Fukushima coast was formed mainly owing to adsorption from the dissolved phase by June 2011, when the impact of the direct oceanic Cs-137 release from FNPP1 was remarkable.

Journal Articles

Determination of $$^{135}$$Cs/$$^{137}$$Cs isotopic ratio in soil collected near Fukushima Daiichi Nuclear Power Station through mass spectrometry

Shimada, Asako; Tsukahara, Takehiko*; Nomura, Masao*; Kim, M. S.*; Shimada, Taro; Takeda, Seiji; Yamaguchi, Tetsuji

Journal of Nuclear Science and Technology, 58(11), p.1184 - 1194, 2021/11

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Determining the completeness of nuclear reactor decommissioning is an important step in safely utilizing nuclear power. For example, $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident can be treated as background radioactivity, so determining the origin of $$^{137}$$Cs is essential. To accomplish this, measuring the $$^{135}$$Cs/$$^{137}$$Cs isotope ratio can be useful, so this study optimized a solvent extraction method, with calix[4]arene-bis(t-octylbenzo-crown-6) [BOBCalixC6] in 1-octanol, to purify radioactive Cs, radiocesium, from a solution of major environmental soil elements and mass spectrometry interference elements. This optimized method was applied to Cs purification in soil samples (40 g), and the final solutions contained a total of 10$$mu$$g/ml of the major soil elements and ng/ml concentrations at most of interfering elements. Soil samples collected near the FDNPS were then purified, and the $$^{135}$$Cs/$$^{137}$$Cs isotope ratios were measured, using both thermal ionization mass spectrometry (TIMS) and triple quadrupole induced coupled plasma mass spectrometry (ICP-QQQ). The results of each of these measurements were compared, and we found that Cs isotope ratios obtained by TIMS were more precise, by an order of magnitude, while the ICP-QQQ results possessed good abundance sensitivities. A slightly higher $$^{135}$$Cs/$$^{137}$$Cs ratio in the northwest area of the FDNPS was observed, while other areas exhibited similar values, all within the measurement error range, which indicated different origins of radiocesium. These results agreed with previously reported $$^{134}$$Cs/$$^{137}$$Cs activity distributions, suggesting that this ratio may be useful in identifying radiocesium origins for evaluating future nuclear reactor decommissions.

Journal Articles

Isotope shift and hyperfine structure measurements on triple resonance excitation to the autoionizing Rydberg state of atomic strontium

Iwata, Yoshihiro; Miyabe, Masabumi; Akaoka, Katsuaki; Wakaida, Ikuo

Journal of Quantitative Spectroscopy & Radiative Transfer, 275, p.107882_1 - 107882_9, 2021/11

 Times Cited Count:0

Following the accident at TEPCO's Fukushima Daiichi Nuclear Power Station, an isotope-selective analysis method using laser resonance ionization has been developed for strontium-90. In this study, the isotope shifts and hyperfine structure constants of stable isotopes were measured for two schemes expected to have high isotopic selectivity, and the isotope shifts of strontium-90 were evaluated using the King plot analysis. The measured strontium-90 optical isotopic selectivities ranged from $$10^3$$ to $$10^5$$, which are sufficient for analysis of real samples.

Journal Articles

Development experience for plastic scintillation fiber after the accident of the Fukushima Daiichi Nuclear Power Plant

Sanada, Yukihisa

Hokeikyo Nyusu, (68), p.2 - 6, 2021/10

Due to the impact of the Fukushima Daiichi Nuclear Power Station accident (hereinafter referred to as the power station accident) of Tokyo Electric Power Company Holdings, Inc., the surrounding environment was contaminated with radioactive substances such as radioactive cesium. After the nuclear power plant accident, plastic scintillation fiber is one of the applied wire and surface radiation measurement techniques. This paper summarizes the development process from a series of development to the introduction of the actual machine.

Journal Articles

Impact of extreme typhoon events on the fluvial discharge of particulate radiocesium in Fukushima Prefecture

Nakanishi, Takahiro; Oyama, Takuya; Hagiwara, Hiroki; Sakuma, Kazuyuki

Journal of Coastal Research, 114(SI), p.310 - 314, 2021/10

The two huge typhoons in 2019, Hagibis and Bualoi, caused enormous flood damage to Fukushima. On the basis of field observations over 6 years in Ukedo River near the Fukushima Nuclear Power Plant, sediment and $$^{137}$$Cs discharges from the river catchment were quantitatively evaluated. Approximately 90% of annual sediment and $$^{137}$$Cs discharges in 2019 was occupied during the typhoons Hagibis and Bualoi events. This sediment discharge was almost twice than the discharge during the largest ever flood event since the Fukushima nuclear accident, caused by typhoon Etau in September 2015. However, $$^{137}$$Cs discharge during Hagibis and Bualoi events was two-thirds that of Etau event, because the particulate $$^{137}$$Cs concentration in river water decreased during the observation period. Moreover, $$^{137}$$Cs discharge during two typhoon events in 2019 accounted for only 0.1% of the catchment $$^{137}$$Cs deposition and the impact of radiocesium to the coastal area was extremely limited.

Journal Articles

Dynamics of radioactive cesium in coastal area linked with river discharge

Misono, Toshiharu; Tsuruta, Tadahiko; Shiribiki, Takehiko; Nakanishi, Takahiro; Nagao, Seiya*; Ochiai, Shinya*; Sanada, Yukihisa

Journal of Coastal Research, 114(SI), p.315 - 319, 2021/10

For understanding future radioactive Cs dynamics and its distribution in the coastal area of Fukushima Prefecture, it is important to evaluate the supply of radioactive Cs from river discharge. Especially particulate radioactive Cs supplied in floods might have a significant impact on the coastal area. However, there are few studies on the dynamics of particulate radioactive Cs at the coastal area linked with rivers at the flood event. As a result of measuring the $$^{137}$$Cs concentration of the sinking particles collected by the sediment trap, at the observation point installed in front of the river, the $$^{137}$$Cs concentration collected immediately after the typhoon Bualoi (October 25th) was about higher than before the typhoon. However, the $$^{137}$$Cs concentration of the sinking particles collected two days after the typhoon was almost the same as before the typhoon. The impact of rivers on coastal areas during torrential rain stuck is extremely limited.

Journal Articles

Validity of the source term for the Fukushima Dai-ichi Nuclear Power Station accident estimated using local-scale atmospheric dispersion simulations to reproduce the large-scale atmospheric dispersion of $$^{137}$$Cs

Kadowaki, Masanao; Furuno, Akiko; Nagai, Haruyasu; Kawamura, Hideyuki; Terada, Hiroaki; Tsuzuki, Katsunori; El-Asaad. H.

Journal of Environmental Radioactivity, 237, p.106704_1 - 106704_18, 2021/10

 Times Cited Count:0 Percentile:0(Environmental Sciences)

The source term of $$^{137}$$Cs for the Fukushima Daiichi Nuclear Power Station (FDNPS) accident was estimated from the results of local-scale atmospheric dispersion simulations and measurements. To confirm the source term's validity for reproducing the large-scale atmospheric dispersion of $$^{137}$$Cs, this study conducted hemispheric-scale atmospheric and oceanic dispersion simulations. In the dispersion simulations, the atmospheric-dispersion database system Worldwide version of System for Prediction of Environmental Emergency Dose Information (WSPEEDI)-DB and oceanic dispersion model SEA-GEARN-FDM were used. Compared with the air concentrations of $$^{137}$$Cs measured by the Comprehensive Nuclear-Test-Ban Treaty Organization, overall, the WSPEEDI-DB simulation reproduced the measurements with some overestimation. Furthermore, the deposition amounts of $$^{137}$$Cs was investigated using concentrations of $$^{137}$$Cs in seawater. The simulated seawater concentrations of $$^{137}$$Cs were underestimated regionally in the North Pacific. The overestimation and underestimation could be improved without contradiction between the air and seawater concentrations of $$^{137}$$Cs using more realistic precipitation in atmospheric dispersion simulations. This shows that the source term validated in this study could reproduce the spatiotemporal distribution of $$^{137}$$Cs because of the FDNPS accident in both local and large-scale atmospheric dispersion simulations.

Journal Articles

Simulation study of a shield-free directional gamma-ray detector using Small-Angle Compton Scattering

Kitayama, Yoshiharu; Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo

Journal of Nuclear Engineering and Radiation Science, 7(4), p.042006_1 - 042006_7, 2021/10

Journal Articles

Feasibility study of the one-dimensional radiation distribution sensing method using an optical fiber sensor based on wavelength spectrum unfolding

Terasaka, Yuta; Watanabe, Kenichi*; Uritani, Akira*; Yamazaki, Atsushi*; Sato, Yuki; Torii, Tatsuo; Wakaida, Ikuo

Journal of Nuclear Engineering and Radiation Science, 7(4), p.042002_1 - 042002_7, 2021/10

For the application in the measurement of the high dose rate hot spots inside the Fukushima Daiichi Nuclear Power Station (FDNPS) buildings, we propose a novel one-dimensional radiation distribution sensing method using an optical fiber sensor based on wavelength spectrum unfolding. The proposed method estimates the incident position of radiation to the fiber by the unfolding of the wavelength spectrum output from the fiber edge using the fact that the attenuation length of light along the fiber depends on the wavelength. Because this method measures the integrated light intensity, this method can avoid the problem of counting loss and signal pile-up, which occurs in the radiation detector with pulse counting mode under high dose rate field. Through basic experiments using the ultraviolet light source and $$^{90}$$Sr/$$^{90}$$Y radioactive point source, basic properties of source position detection were confirmed.

4803 (Records 1-20 displayed on this page)