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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:1 Percentile:76.35(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

High temperature gas-cooled reactors

Takeda, Tetsuaki*; Inagaki, Yoshiyuki; Aihara, Jun; Aoki, Takeshi; Fujiwara, Yusuke; Fukaya, Yuji; Goto, Minoru; Ho, H. Q.; Iigaki, Kazuhiko; Imai, Yoshiyuki; et al.

High Temperature Gas-Cooled Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.5, 464 Pages, 2021/02

As a general overview of the research and development of a High Temperature Gas-cooled Reactor (HTGR) in JAEA, this book describes the achievements by the High Temperature Engineering Test Reactor (HTTR) on the designs, key component technologies such as fuel, reactor internals, high temperature components, etc., and operational experience such as rise-to-power tests, high temperature operation at 950$$^{circ}$$C, safety demonstration tests, etc. In addition, based on the knowledge of the HTTR, the development of designs and component technologies such as high performance fuel, helium gas turbine and hydrogen production by IS process for commercial HTGRs are described. These results are very useful for the future development of HTGRs. This book is published as one of a series of technical books on fossil fuel and nuclear energy systems by the Power Energy Systems Division of the Japan Society of Mechanical Engineers.

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:5 Percentile:96.3(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

Fabrication of a novel magnetic topological heterostructure and temperature evolution of its massive Dirac cone

Hirahara, Toru*; Otrokov, M. M.*; Sasaki, Taisuke*; Sumida, Kazuki*; Tomohiro, Yuta*; Kusaka, Shotaro*; Okuyama, Yuma*; Ichinokura, Satoru*; Kobayashi, Masaki*; Takeda, Yukiharu; et al.

Nature Communications (Internet), 11, p.4821_1 - 4821_8, 2020/09

 Times Cited Count:11 Percentile:89.19(Multidisciplinary Sciences)

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:23.13(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

Irradiation performance of sodium-bonded control rod for the fast breeder reactor

Sasaki, Shinji; Maeda, Koji; Furuya, Hirotaka*

Journal of Nuclear Science and Technology, 55(3), p.276 - 282, 2018/03

 Times Cited Count:3 Percentile:45.99(Nuclear Science & Technology)

Journal Articles

Application of FE-SEM to the measurement of U, Pu, Am in the irradiated MA-MOX fuel

Sasaki, Shinji; Tanno, Takashi; Maeda, Koji

Proceedings of 54th Annual Meeting of Hot Laboratories and Remote Handling (HOTLAB 2017) (Internet), 6 Pages, 2017/00

During irradiation in a fast reactor, the microstructure change of the mixed oxide fuels and the changes of element distributions occur because of a radial temperature gradient. Therefore, it is important to study the irradiation behavior of MA-MOX for advancement of fast reactor fuels. In order to make detailed observations of microstructure and elemental analyses of MA-MOX, irradiated MA-MOX specimens were carried out PIE by using a FE-SEM equipped with WDX. Because fuel samples have high radio activities and emit alpha-particles, the instrument was modified. the instrument was installed in a lead shield box and the control unit was separately located outside the box. The microstructure changes were observed in irradiated MA-MOX specimen. The characteristic X-rays peaks were detected successfully. By measuring the intensities of characteristic X-rays, it was tried quantitative analysis of U, Pu, Am along radial direction of irradiated specimen.

JAEA Reports

Development of field emission SEM to observe high radioactive irradiated fuels

Isozaki, Misaki; Sasaki, Shinji; Maeda, Koji; Katsuyama, Kozo

JAEA-Technology 2015-058, 28 Pages, 2016/03


During irradiation in the fast reactor "JOYO", the changes of fuel structures with the formation of central void occur in the uranium-plutonium mixed oxide fuels (MOX fuels) because of radial temperature gradient. The changes of element (U, Pu, and so on) distributions along radial direction proceed from these changes. Therefore, it is important to study the changes of fuel structures of the minute area in fuel pellet and the changes of element distribution behavior for development of fast reactor fuels. In order to make detailed observations of microstructure and elemental analyses of fuel samples, a field emission scanning electron microscope (FE-SEM) equipped with a wavelength-dispersive X-ray spectrometer (WDS) and an energy-dispersive X-ray spectrometer (EDS) were installed in Fuel Monitoring Facility (FMF). The samples of this FE-SEM are very high radioactivity because the samples contain the nuclear fuel elements (U, Pu, etc.), the fission products (Cs, Rh, etc.) and activation product (Co, Mn etc.). Owing to this, it is necessary to prevent leakage of radioactive materials (particularly, U, Pu is need tight accountancy in law) and to protect operators from radiation. In this installation of FE-SEM, it is selected JSM-7001F (made by JEOL) for base model. The notable modified points were as follows. (1) To protect operators from radiation, lead shields was installed around FE-SEM. (2) To prevent leakage of radioactive materials, the instrument was attached to a remote control air-tight sample transfer unit between a shielded hot cell and the FE-SEM and the instrument was fixing rigid structure without vibration damper. (3) The design and manufacture the lead shields with consideration of instrument maintainability. This paper was described the summary of FE-SEM, the notable modified points, the ways of FE-SEM installation, the result of performance test.

Journal Articles

Early-in-life fuel restructuring behavior of Am-bearing MOX fuels

Tanaka, Kosuke; Sasaki, Shinji; Katsuyama, Kozo; Koyama, Shinichi

Transactions of the American Nuclear Society, 113(1), p.619 - 621, 2015/10

In order to evaluate the microstructural change behavior of Am-MOX fuels at the initial stage of irradiation, detailed investigations using image analysis were performed on X-ray Computed Tomography (X-ray CT) images and on ceramographs from fuels irradiated in both B11 and B14.

Journal Articles

Distribution of radioactive nuclides of boring core samples extracted from concrete structures of reactor buildings in the Fukushima Daiichi Nuclear Power Plant

Maeda, Koji; Sasaki, Shinji; Kumai, Misaki; Sato, Isamu; Suto, Mitsuo; Osaka, Masahiko; Goto, Tetsuo*; Sakai, Hitoshi*; Chigira, Takayuki*; Murata, Hirotoshi*

Journal of Nuclear Science and Technology, 51(7-8), p.1006 - 1023, 2014/07

 Times Cited Count:11 Percentile:72.25(Nuclear Science & Technology)

Since the start of the severe accident at the Fukushima Daiichi Nuclear Power Plant in March 2011, concrete surfaces within the reactor buildings have been exposed to radioactive contaminants. Released radiation sources still remain too high to permit entry into some areas of the RBs to allow the damage to be assessed and to allow carrying out the restoration of lost safety functions, decommissioning activities, etc. In order to clarify the situation of this contamination in the RBs, 18 samples were subjected to analyses to determine the surface radionuclide concentrations and to characterize the radionuclide distributions in the samples. Decontamination tests on the sample of Unit 2 were conducted to reduce the levels of radioactivity present near the sample surface. As a result of the tests, the level of radioactivity of the sample was reduced with the removal of 97% of the contamination present near the sample surface.

JAEA Reports

R&D of remote decontamination technique in reactor building (2-$$ textcircled{1} $$-1) towards the decommissioning of Fukushima Daiichi Nuclear Power plant; Results of Examinations of contaminated samples at JAEA hot laboratories

Maeda, Koji; Sasaki, Shinji; Kumai, Misaki; Sato, Isamu; Suto, Mitsuo; Osaka, Masahiko

JAEA-Research 2013-025, 123 Pages, 2014/01


In order to clarify the situation of the contamination in the Fukushima Daiichi reactor buildings of Units 1, 2 and 3, selected samples were transported to the Oarai Engineering Center of JAEA where they were subjected to analyses to determine the surface radionuclide concentrations and to characterize the radionuclide distributions in the samples. The analysis results indicate that the situation of contamination in the building of Unit 2 was different from others, and the protective surface coatings on the concrete floors provided significant protection against radionuclide penetration. contaminants.

JAEA Reports

Immersion test in artificial water and evaluation of strength property on fuel cladding tubes irradiated in Fugen Nuclear Power Plant

Yamagata, Ichiro; Hayashi, Takehiro; Mashiko, Shinichi*; Sasaki, Shinji; Inoue, Masaki; Yamashita, Shinichiro; Maeda, Koji

JAEA-Testing 2013-004, 23 Pages, 2013/11


In the accident of the Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Co. accompanying the Great East Japan Earthquake, fuel assemblies kept in the spent fuel pool of reactor units 1-4, were exposed to the inconceivable environment such as falling and mixing of rubble, especially seawater were injected into unit 2-4. In order to evaluate the integrity of the fuel assemblies in spent fuel pools, and in the long-term storage after transported to the common storage pool, the immersion tests were performed using zircaloy-2 fuel cladding tubes irradiated in the advanced thermal reactor Fugen. The immersion liquid was prepared with doubling dilution of artificial seawater, which temperature was 80 $$^{circ}$$C and immersion time was about 336 hours, as assuming the situation of the pool. The results indicated zircaloy-2 cladding tubes had no significant corrosion and no influence on mechanical property by immersion tests with artificial seawater conditions of this work.

Journal Articles

Results of detailed analyses performed on boring cores extracted from the concrete floors of the Fukushima Daiichi Nuclear Power Plant reactor buildings

Maeda, Koji; Sasaki, Shinji; Kumai, Misaki; Sato, Isamu; Osaka, Masahiko; Fukushima, Mineo; Kawatsuma, Shinji; Goto, Tetsuo*; Sakai, Hitoshi*; Chigira, Takayuki*; et al.

Proceedings of International Nuclear Fuel Cycle Conference; Nuclear Energy at a Crossroads (GLOBAL 2013) (CD-ROM), p.272 - 277, 2013/09

JAEA Reports

Investigation on analytical method for the transfer behavior of corrosion product (CP) in the fast breeder reactors

Matsuo, Yoichiro; Sasaki, Shinji

JAEA-Review 2013-007, 46 Pages, 2013/05


Radioactive corrosion products (CP) are main cause of personal radiation exposure during maintenance without fuel failure in FBR plants. The most important CP species are $$^{54}$$Mn and $$^{60}$$Co. The deposited radioactive CP cause radiation fields near the piping and components. Then, the deposited radioactive CP contributes to the radiation exposure of the plant-worker. In this review, firstly, collects knowledge about CP transfer behavior in the fast reactor and analyzes it and organize essence of the CP transfer behavior. Secondly, existing method to parse CP transfer behavior is investigated and extracts the issues and discusses it about the solution of those issues. Finally, about a specific example of the improvement based on the solution, a recent trend is investigated and describes evaluated content.

Journal Articles

$$E_1/E_2$$ traps in 6H-SiC studied with Laplace deep level transient spectroscopy

Koizumi, Atsushi*; Markevich, V. P.*; Iwamoto, Naoya; Sasaki, Sho*; Oshima, Takeshi; Kojima, Kazutoshi*; Kimoto, Tsunenobu*; Uchida, Kazuo*; Nozaki, Shinji*; Hamilton, B.*; et al.

Applied Physics Letters, 102(3), p.032104_1 - 032104_4, 2013/01

 Times Cited Count:8 Percentile:38.93(Physics, Applied)

JAEA Reports

Investigation on cause of malfunction of Wide Range Monitor (WRM) in High Temperature engineering Test Reactor (HTTR); Sample tests and destructive tests

Shinohara, Masanori; Motegi, Toshihiro; Saito, Kenji; Haga, Hiroyuki; Sasaki, Shinji; Katsuyama, Kozo; Takada, Kiyoshi*; Higashimura, Keisuke*; Fujii, Junichi*; Ukai, Takayuki*; et al.

JAEA-Technology 2012-032, 29 Pages, 2012/11


An event, in which one of WRMs were disabled to detect the neutron flux in the reactor core, occurred during the period of reactor shut down of HTTR in March, 2010. The actual life time of WRM was unexpectedly shorter than the past developed life time. Investigation of the cause of the outage of WRM toward the recovery of the life time up to the past developed life is one of the issues to develop the technology basis of HTGR. Then, two experimental investigations were carried out to reveal the cause of the malfunction by specifying the damaged part causing the event in the WRM. One is an experiment using a mock-up sample test which strength degradation on assembly accuracy and heat cycle to specify the damaged part in the WRM. The other is a destructive test in FMF to specify the damaged part in the WRM. This report summarized the results of the destructive test and the experimental investigation using the mock-up to reveal the cause of malfunction of WRM.

Journal Articles

Support system for training and education of future expert at PIE Hot Laboratories in Oarai JAEA; FEETS

Osaka, Masahiko; Donomae, Takako; Ichikawa, Shoichi; Sasaki, Shinji; Ishimi, Akihiro; Inoue, Toshihiko; Sekio, Yoshihiro; Miwa, Shuhei; Onishi, Takashi; Asaka, Takeo; et al.

Proceedings of 1st Asian Nuclear Fuel Conference (ANFC), 2 Pages, 2012/03

Support system for training and education of future expert in hot laboratories of Oarai-JAEA, named FEETS, is presented. The system has been established based on research results on both characterization of Oarai hot laboratory and user-needs. Various programs under FEETS are also introduced.

Journal Articles

Measurement of deformation of FBR fuel assembly wrapper tube by an innovative technique

Sasaki, Shinji; Abe, Kazuyuki; Nagamine, Tsuyoshi

JAEA-Conf 2008-010, p.362 - 371, 2008/12

An innovative technique to measure the deformation of irradiated wrapper tube of FBR fuel assembly was developed, and installed in the hot cell of the Fuels Monitoring Facility in JAEA. In order to confirm the performance of this instrument, a number of measurements were carried out in the wrapper tubes irradiated to high burnup in the experimental fast reactor Joyo. In the instrument used until now, only three face to face distances in the hexagonal wrapper tube have been measured along the axial direction. On the other hand, in the instrument developed in this technique the face to face distances could be continuously measured along the lateral direction in the outer surfaces of wrapper tube. Using data obtained by this technique, the detailed analyses of deformation can be done throughout a whole wrapper tube.

JAEA Reports

Development and management of the knowledge base for the geological disposal technology; Annual report 2006

Umeda, Koji; Oi, Takao; Osawa, Hideaki; Oyama, Takuya; Oda, Chie; Kamei, Gento; Kuji, Masayoshi*; Kurosawa, Hideki; Kobayashi, Yasushi; Sasaki, Yasuo; et al.

JAEA-Review 2007-050, 82 Pages, 2007/12


This report shows the annual report which shows the summarized results and topic outline of each project on geological disposal technology in the fiscal year of 2006.

Journal Articles

Fuel-cladding chemical interaction in MOX fuel rods irradiated to high burnup in an advanced thermal reactor

Tanaka, Kosuke; Maeda, Koji; Sasaki, Shinji; Ikusawa, Yoshihisa; Abe, Tomoyuki

Journal of Nuclear Materials, 357(1-3), p.58 - 68, 2006/10

 Times Cited Count:9 Percentile:56.05(Materials Science, Multidisciplinary)

The performance of MOX fuel irradiated in the advanced thermal reactor, FUGEN, to the burnup of 47.5 GWd/t, was investigated by using a telescotpe, optical microscope, SEM and EPMA. Observations focused on elucidating the corrosion behavior of the cladding inner surface. A reaction layer was observed at burnups higher than about 35 GWd/t. The relationship between the thickness of the reaction layer and burnup was similar to that reported in the literature for conventional UO$$_{2}$$ fuel and other MOX fuels. The existence of a plutonium spot near the outer surface of the fuel pellet had no significant effect on the thickness of the reaction layer. A bonding layer was observed on the cladding inner surface. Its morphology and elemental distributions were not so different from those in BWR UO$$_{2}$$ fuel pins irradiated to high burnup, in which the fission gas release rate is high. In addition, the dependences of bonding layer formation on the burnup and linear heat rating were similar to results of UO2 fuel pins. It was, thus, suggested that the bonding layer formation mechanism was similar in both UO2 and MOX fuel pins.

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