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underwater radiation monitoring detectorJi, W.*; Lee, E.*; Ji, Y.-Y.*; Ochi, Kotaro; Yoshimura, Kazuya; Funaki, Hironori; Sanada, Yukihisa
Nuclear Engineering and Technology, 58(2), p.103933_1 - 103933_6, 2026/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)We aimed to validate the performance of an in situ underwater radiation detector, MARK-U1 (Monitoring of Ambient Radiation of KAERI - Underwater), was used to estimate 
Cs activity concentration in river and reservoir sediment at predicted sites of contamination. Additionally, underwater core samples were collected to measure the radioactivity using a high-purity germanium (HPGe) detector. To estimate radioactivity, a conversion factor was derived by comparing the measured spectrum and Cs activity in the sample. A Monte Carlo N-Particle (MCNP) simulation was conducted to determine the effective source geometry for in situ measurement. The simulation results correlated well with the on-site MARK-U1 monitoring results, with a deviation of 31.62%. These findings validate the performance of the in situ detector. This device can therefore be used to estimate Cs activity concentration in the underwater sediment via on-site monitoring, without requiring sample collection.
Ji, Y.-Y.*; Ji, W.*; Kim, K.*; Kim, M. J.*; Ochi, Kotaro; Morishita, Yuki; Sanada, Yukihisa
Radiation Physics and Chemistry, 244, p.113781_1 - 113781_12, 2026/02
Times Cited Count：0UAV-based airborne gamma-ray spectrometry enables rapid radiation mapping, but accurate estimation of ground-level ambient dose rates is difficult because of altitude attenuation, detector field-of-view effects, heterogeneous contamination, and terrain variability. We developed a practical method combining hovering-flight calibration and ground-based validation near the Fukushima Daiichi Nuclear Power Plant. Altitude correction factors were derived using a dual-exponential model and compared with tripod and backpack measurements. Results showed that heterogeneous contamination and terrain introduce systematic biases if correction factors are derived under non-uniform conditions, while calibration at uniform sites improves agreement. The proposed approach demonstrates that UAV airborne surveys can reliably estimate spatial dose-rate distributions when site-dependent corrections are applied.
Ji, Y.-Y.*; Joung, S.*; Ji, W.*; Ochi, Kotaro; Sasaki, Miyuki; Sanada, Yukihisa
Journal of Radiological Protection, 45(4), p.042501_1 - 042501_11, 2025/12
Times Cited Count：1 Percentile：0.00(Environmental Sciences)This study reports the development and field validation of KAERI's UAV-based gamma-ray spectrometry system equipped with LaBr
(Ce) detectors. Joint surveys with JAEA near Fukushima Daiichi Nuclear Power Plant (FDNPP) showed reliable dose rate estimation after applying altitude based attenuation correction, through discrepancies occurred in sloped terrain. Incorporating terrain data is recommended to enhance accuracy for emergency response applications.
Joung, S.*; Ji, Y.-Y.*; Choi, Y.*; Lee, E.*; Ji, W.*; Sasaki, Miyuki; Ochi, Kotaro; Sanada, Yukihisa
Journal of Instrumentation (Internet), 20(4), p.P04027_1 - P04027_10, 2025/04
Times Cited Count：1 Percentile：53.61(Instruments & Instrumentation)Kim, M.*; Lee, C.*; Sugita, Yutaka; Kim, J.-S.*; Jeon, M.-K.*
Geomechanics for Energy and the Environment, 41, p.100628_1 - 100628_9, 2025/03
Times Cited Count：1 Percentile：51.47(Energy & Fuels)This study investigates the impact of primary variables selection on the modeling of non-isothermal two-phase flow, by using the numerical work on the full-scale Engineered Barrier System (EBS) experiment conducted at Horonobe URL as part of the DECOVALEX-2023 project. A validated numerical model is employed to simulate the coupled thermo-hydrological behavior of heterogeneous porous media within the EBS. Two different primary variable schemes are compared in discretizing the governing equations, revealing significant difference in results.
Marchetto, C.*; Ha, K. S*; Herranz, L. E.*; Hirose, Yoshiyasu; Jankowski, T.*; Lee, Y.*; Nowack, H.*; Pellegrini, M.*; Sun, X.*
Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 17 Pages, 2022/03
Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi
Health Physics, 121(6), p.613 - 620, 2021/12
Times Cited Count：3 Percentile：25.54(Environmental Sciences)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.
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
Times Cited Count：10 Percentile：68.31(Chemistry, Physical)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.
Riyana, E. S.*; Suda, Shoya*; Ishibashi, Kenji*; Matsuura, Hideaki*; Katakura, Junichi*; Sun, G. M.*; Katano, Yoshiaki
Journal of Nuclear Science and Technology, 56(5), p.369 - 375, 2019/05
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Nuclear reactors produce a great number of electron antineutrinos mainly from beta-decay chains of fission products. Such neutrinos have energies mostly in MeV range. We are interested in neutrinos in a region of keV, since they may have information on fuel burn-up and may be detected in future with advanced measurement technology. We calculate reactor antineutrino spectra especially in the low energy region. In this work we present neutrino spectra from various reactors such as typical PWR reactor and others types of reactors for comparison. Our result shows the electron antineutrino flux in the low energy region increases with burn-up of nuclear fuel by accumulated nuclides with low Q values in beta decay.
Ohara, Takashi; Kiyanagi, Ryoji; Oikawa, Kenichi; Kaneko, Koji; Kawasaki, Takuro; Tamura, Itaru; Nakao, Akiko*; Hanashima, Takayasu*; Munakata, Koji*; Moyoshi, Taketo*; et al.
Journal of Applied Crystallography, 49(1), p.120 - 127, 2016/02
Times Cited Count：62 Percentile：96.15(Chemistry, Multidisciplinary)Kojima, Atsushi; Hanada, Masaya; Jeong, S. H.*; Bae, Y. S.*; Chang, D. H.*; Kim, T. S.*; Lee, K. W.*; Park, M.*; Jung, B. K.*; Mogaki, Kazuhiko; et al.
Fusion Engineering and Design, 102, p.81 - 87, 2016/01
Times Cited Count：7 Percentile：48.44(Nuclear Science & Technology)The long-pulse acceleration of the high-power positive ion beam has been demonstrated with the JT-60 positive ion source in the joint experiment among Japan Atomic Energy Agency (JAEA), Korea Atomic Energy Research Institute (KAERI) and National Fusion Research Institute (NFRI) under the collaboration program for the development of plasma heating and current drive systems. As a result of development of the operation techniques of the ion source and facilities of the neutral beam test stand in KAERI, 2 MW 100 s beam has been achieved for the first time. The achieved beam performance satisfies the JT-60SA requirement which is designed to be a 1.94 MW ion beam power from an ion source corresponding to total neutral beam power of 20 MW with 24 ion sources. Therefore, it was found that the JT-60 positive ion sources were applicable in the JT-60SA neutral beam injectors without further modification of the ion source and the accelerator. Moreover, because this ion source is planned to be a backup ion source for KSTAR, the operational region and characteristic has been clarified to apply to the KSTAR neutral beam injector.
Yoshitomi, Hiroshi; Tanimura, Yoshihiko*; Tatebe, Yosuke; Tsutsumi, Masahiro; Kawasaki, Katsuya; Kowatari, Munehiko; Yoshizawa, Michio; Shimizu, Shigeru*; Kim, J.-S.*; Lee, J.-G.*; et al.
Proceedings of 4th Asian and Oceanic Congress on Radiation Protection (AOCRP-4) (CD-ROM), 4 Pages, 2015/07
Kawakubo, Yoko; Inoue, Naoko; Tomikawa, Hirofumi
Kaku Busshitsu Kanri Gakkai (INMM) Nihon Shibu Dai-34-Kai Nenji Taikai Rombunshu (Internet), 9 Pages, 2013/10
Japan Atomic Energy Agency (JAEA) is carrying out R&D to design and establish an Information-Sharing Framework (ISF) for supporting and promoting nuclear transparency in cooperation with Sandia National Laboratories (SNL), the Korean Institute for Nonproliferation and Control (KINAC), and Korea Atomic Energy Research Institute (KAERI). Partner organizations have agreed on starting by establishing ISF with a focus on nuclear nonproliferation experts in Track II as primary information providers/receivers. Thus far, requirements for ISF have been developed for providing clear steps to design and establish ISF and ensuring its sustainability. As the next step, ISF is to be established following the requirements and demonstration of information sharing will be carried out. In the long-term, ISF could be expanded to invite other interested organizations and include other information. This paper describes the effort to design and establish ISF by focusing on the requirements which has been developed under the joint R&D.
Sumita, Junya; Fujita, Ichiro; Shibata, Taiju; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji*; Sawa, Kazuhiro; Kim, W. J.*; Park, J. Y.*
IOP Conference Series; Materials Science and Engineering, 18(16), p.162010_1 - 162010_4, 2011/09
Times Cited Count：1 Percentile：49.21(Materials Science, Ceramics)For control rod element of Very High Temperature Reactor, carbon fiber reinforced carbon matrix composite (C/C composite) is one of the major candidate materials for its high strength and thermal stability. Since the crack propagation of the C/C composite is complicated, the fracture behavior is one of the most important subjects of the design methodology for the control rod with the C/C composite. In this study, in order to assess the Mode-II fracture behavior of the two-dimensional (2D-) C/C composite which has the layer structure of laminas composed of fibers and matrix, bending test with oxidized end notched flexure specimen was carried out. The interlaminar fracture toughness decreased with increasing the oxidation for the 2D-C/C composite. The oxidized matrix causes reduction of fracture toughness and the reduction ratio is dependent on the matrix type. The crack initiates at the boundary between fiber bundles and grows along them without breaking the fiber. It is thought that the cracks which were initiated at the interface between matrix and fiber were gathered into the voids in the boundary between fiber bundles, and then the crack grows up in the matrix.
Watanabe, Kazuhiro; Dairaku, Masayuki; Tobari, Hiroyuki; Kashiwagi, Mieko; Inoue, Takashi; Hanada, Masaya; Jeong, S. H.*; Chang, D. H.*; Kim, T. S.*; Kim, B. R.*; et al.
Review of Scientific Instruments, 82(6), p.063507_1 - 063507_6, 2011/06
Times Cited Count：16 Percentile：56.18(Instruments & Instrumentation)A long pulse plasma generator for neutral beam injectors has been developed. The plasma generator was designed to produce 65 A at 120 keV from a beam extraction area of 12 cm 
46 cm. A type of the plasma generator is a multi-cusp plasma generator with SmCo permanent magnets. A long pulse test of the plasma generator was performed at the KSTAR NBI test stand in Korea under the Japan - Korea Fusion collaboration. It was successfully demonstrated of the long pulse operation of the plasma generator for 200 s at an arc discharge power of 70 kW which can produce 65 A beams. Plasma spatial uniformity at the beam extraction area was confirmed to be smaller than 
8% of the deviation from an averaged ion saturation current density. A high arc efficiency of 0.9-1.1 A/kW was obtained at the beam extraction with 73 keV, 41 A for 5 sec. From these experimental studies, a performance of this plasma generator for long pulse ion sources was confirmed.
Saegusa, Jun; Shimizu, Shigeru; Yamaguchi, Yasuhiro; Kim, B.-H.*
Proceedings of 2006 Autumn Conference of the Korean Association for Radiation Protection, p.238 - 239, 2006/11
At the Nuclear Science Research Institute (NSRI) of Japan Atomic Energy Agency (JAEA), reference calibration fields of X-, 
-, 
-rays and neutrons have been provided in the Facility of Radiation Standards (FRS) for calibrating dosemeters used for radiation protection purpose. In this paper we overview these calibration fields and describe its position in the traceability and quality assurance system, present status of their utilization, and so forth.
Joung, S.*; Ji, Y.-Y.*; Choi, Y.*; Lee, E.*; Ji, W.*; Sasaki, Miyuki; Ochi, Kotaro; Sanada, Yukihisa
no journal, ,
KAERI (Korea Atomic Energy Research Institute) has developed the MARK A1 aerial survey system for unmanned aerial vehicles for use in contaminated areas. The MARK A1 system consists of a CZT detector, signal processing unit, and positioning and interface units to a PC on the ground. To validate the effectiveness of the detectors, field tests were conducted in high dose rate environments near the Fukushima Daiichi Nuclear Power Station. The JAEA and KAERI detectors were each mounted on an unmanned helicopter to make measurements at different altitudes. For both systems, the air dose rates obtained from the airborne survey gave results with a similar trend to the air dose rates obtained from the walking survey. Therefore, it is expected that MARK A1 can be used to quickly scan large and highly contaminated areas that are difficult for humans to access in the event of a nuclear accident.
Hajima, Ryoichi; Kawata, Hiroshi*; Kasuga, Toshio*; Sato, Kotaro*; Nakamura, Norio*; Sakanaka, Shogo*; Kobayashi, Yukinori*
no journal, ,
no abstracts in English
Sasaki, Miyuki; Sanada, Yukihisa; Lee, E.*; Joung, S.*; Ji, Y.-Y.*
no journal, ,
Since the Fukushima Daiichi Nuclear Power Plant accident, some types of radiation monitoring have been conducted in Japan. Walking surveys and unmanned helicopter surveys have been conducted around the FDNPP to the ambient dose equivalent rates (air dose rate). The airborne radiation survey (ARS) by unmanned helicopter has the advantage of measuring large areas including forests. However, ARS has lower measurement resolution than walking surveys. Sasaki et al. constructed an artificial neural network (ANN) to convert ARS data into air dose rates at 1 m above ground level using data accumulated after the accident (Ref). It has been reported that the conversion using ANNs can convert to values closer to those measured on the ground than the conventional method. Showing that the ANN constructed from the Fukushima experience can be applied to detectors other than the radiation detector used to construct the ANN will greatly contribute to the future development of ARS. In this study, we investigated how to apply radiation measurement data acquired with a detector different from the radiation detector used to acquire the training data to an ANN that has already been constructed.
Kim, W. J.*; Seo, M.-R.*; Park, J. Y.*; Sumita, Junya; Shibata, Taiju; Sawa, Kazuhiro
no journal, ,
Carbon-carbon (C/C) composites have been widely used for high-temperature structural applications because they possess excellent mechanical properties such as high specific strength and thermal shock resistance. In the nuclear industry, the composites have also been considered for plasma facing materials in fusion reactors and high-temperature structural parts in gas cooled reactors. In the high-temperature gas cooled reactor, the composites are being considered for the application of various high-temperature structural parts such as control rod components, core restraint belts, tie rods, upper plenum shroud, hot duct insulation cover sheets, and floor blocks. However, the carbon based materials are susceptible to oxidation at temperatures above 400 
C. Therefore, the oxidation behavior and property degradation at high temperature under impure He or in air in case of accidental air ingress should be evaluated before the deployment of composites. In this study, the oxidation behavior of several nuclear-grade C/C composites was evaluated at various temperatures. Thermal and mechanical properties of the composites were also measured before and after oxidation. The oxidation experiments were performed in range of 500 to 1100 C under air or Ar atmosphere. Thermal diffusivity, flexural strength, tensile strength, and interlaminar shear strength of as-received and oxidized specimens were evaluated.
