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Journal Articles

Development of training course on non-destructive assay of nuclear material for Asian region, 2; Development of lectures and exercises on gamma-ray measurement

Yamamoto, Masahiko; Kono, Soma; Saegusa, Yu; Kuno, Takehiko; Sekine, Megumi; Inoue, Naoko; Noro, Naoko; Rodriguez, D.; Yamaguchi, Tomoki; Stinett, J.*

Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 10 Pages, 2023/05

The gamma-ray measurement part of the Non-Destructive Assay (NDA) course of safeguards and nuclear material accountancy was developed to focus on gamma-ray measurement allotting two days out of five days. The lectures on the basic characteristics and detection methods and mechanism of gamma-ray detectors were provided as e-learnings which were developed. The part for hands-on exercises were implemented in JAEA facility. Participants have set up each gamma-ray detector, and performed measurements of uranium and the other gamma-ray emitting nuclides. Also, uranium-235 enrichment measurements have been performed. In addition, the participants trained with a handheld gamma-ray spectrometer, HM-5, that is popular for IAEA safeguards as the preparation in the measurement exercise of fresh fuel assemblies in JRR-3, a research reactor facility of JAEA. This paper reports on the development, implementation, and feedback from participants on gamma-ray measurement part of the NDA course.

Journal Articles

Development of a local exhaust device for removal of radioactive waste from glove-box for handling nuclear fuel materials

Ishibashi, Atsushi; Saegusa, Yu; Aoya, Juri; Yamamoto, Masahiko; Taguchi, Shigeo; Kuno, Takehiko

Nihon Hozen Gakkai Dai-18-Kai Gakujutsu Koenkai Yoshishu, p.241 - 244, 2022/07

no abstracts in English

Journal Articles

Current status of geological disposal by "all-Japan" activities, 2; Site characterization technology for geological disposal

Saegusa, Hiromitsu*; Matsuoka, Toshiyuki*; Niwa, Masakazu; Sasao, Eiji; Hayano, Akira

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 64(1), p.46 - 50, 2022/01

This paper is a review article to introduce the concept of the site selection for geological disposal in geological environment of Japanese Islands, and the current status of related research and development.

Journal Articles

Design, construction and monitoring of temporary storage facilities for removed contaminants

Saegusa, Hiromitsu*; Funaki, Hironori; Kurikami, Hiroshi; Sakamoto, Yoshiaki; Tokizawa, Takayuki*

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.170 - 187, 2021/10

Removed contaminants including soil, grass and trees are to be stored safely at temporary storage facilities for several years, after which they will be transferred to a planned interim storage facility. The decontamination pilot project was carried out in both the restricted and planned evacuation areas in order to assess decontamination methods and demonstrate measures for radiation protection of workers. Fourteen temporary storage facilities of different technical specifications were designed and constructed under various topographic conditions and land use. In order to support the design, construction and monitoring of temporary storage facilities for removed contaminants during the full-scale decontamination within the prefecture of Fukushima, technical know-how obtained during the decontamination pilot project has been identified and summarized in this paper.

Journal Articles

Evaluation of Tsunami debris impact on Tokai Reprocessing Plant

Nishino, Saki; Tsuboi, Masatoshi; Okada, Jumpei; Saegusa, Yu; Omori, Kazuki; Yasuo, Kiyoshi; Seshimo, Kazuyoshi; Domura, Kazuyuki; Yamamoto, Masahiko

Nihon Hozen Gakkai Dai-17-Kai Gakujutsu Koenkai Yoshishu, p.541 - 548, 2021/07

no abstracts in English

Journal Articles

Initial decrease in the ambient dose equivalent rate after the Fukushima accident and its difference from Chernobyl

Yoshimura, Kazuya; Saegusa, Jun; Sanada, Yukihisa

Scientific Reports (Internet), 10(1), p.3859_1 - 3859_9, 2020/03

 Times Cited Count:16 Percentile:66.81(Multidisciplinary Sciences)

Journal Articles

Establishment of a Laboratory for $$gamma$$-ray Spectrometry of Environmental Samples Collected in Fukushima

Saegusa, Jun; Yoda, Tomoyuki; Maeda, Satoshi; Okazaki, Tsutomu; Otani, Shuichi; Yamaguchi, Toshio; Kurita, Yoshiyuki; Hasumi, Atsushi; Yonezawa, Chushiro*; Takeishi, Minoru

Proceedings of 14th International Congress of the International Radiation Protection Association (IRPA-14), Vol.3 (Internet), p.1078 - 1085, 2017/11

After the nuclear accident at the Fukushima Daiichi Nuclear Power Plant in March 2011, the Japan Atomic Energy Agency has newly set up a laboratory for radioactivity analysis in Fukushima. At the laboratory, radioactivity concentrations of environmental samples such as soil, water, dust filter, plant, etc., approximately 1,000 samples in a month, are measured with high-resolution $$gamma$$-ray spectrometry systems. The systems employ n-type HPGe detectors from Ortec. Since September 2012, characterization and upgrade of the systems have been performed aimed at enhancing reliability of analysis and convenience of customers. Resolving both systematic and technical issues, the laboratory has been accredited the ISO/IEC 17025 standard as a testing laboratory for radioactivity analysis.

Journal Articles

Using two detectors concurrently to monitor ambient dose equivalent rates in vehicle surveys of radiocesium contaminated land

Takeishi, Minoru; Shibamichi, Masaru; Malins, A.; Kurikami, Hiroshi; Murakami, Mitsuhiro*; Saegusa, Jun; Yoneya, Masayuki

Journal of Environmental Radioactivity, 177, p.1 - 12, 2017/10

AA2016-0534.pdf:1.79MB

By convention radiation measurements from vehicle-borne surveys are converted to the dose rate at 1 m above the ground in the absence of the vehicle. To improve the accuracy of the converted results from vehicle-borne surveys, we investigated combining measurements from two detectors mounted on the vehicle at different heights above the ground. A dual-detector setup was added to a JAEA monitoring car and compared against hand-held survey meter measurements in Fukushima Prefecture. The dose rates obtained by combining measurements from two detectors were within $$pm$$20% of the hand-held reference measurements. The combined results from the two detectors were more accurate than those from either the roof-mounted detector, or the detector inside the vehicle, taken alone. When radiocesium is deficient on a road compared to the adjacent land, mounting detectors high on vehicles yields dose rates closer to the values adjacent to the road. We also investigated mounting heights for vehicle-borne detectors using Monte Carlo $$gamma$$-ray simulations.

Journal Articles

Analysis of ambient-dose-rate trends in Fukushima; Ecological half-life, effect of snow covering

Saegusa, Jun; Yoda, Tomoyuki; Murakami, Mitsuhiro; Takeishi, Minoru

Kankyo Hoshano Josen Gakkai-Shi, 5(2), p.79 - 93, 2017/06

After the Fukushima Daiichi Nuclear Power Plant (NPP) accident in March 2011, environmental radiation monitoring works have been continuously conducted throughout the Fukushima prefecture of Japan. Five-year transitions of ambient dose rates at 15 locations 20-60 km away from the NPPs were precisely analyzed to investigate their chronological change. Measured dose rates were successfully fitted into a function consisting of a factor reflecting the physical decay of radiocesium and the other component such as the weathering effect. The ecological half-lives derived from the function ranged from 3 to 27 years (average 10 years). The radiation shielding effect by snow covering was also studied with the obtained functions. Due to the effect, dose rates were lowered by 15-50% by 20-cm-deep snow covering, and the ambient doses integrated over the five years were found to decrease by up to 7% compared to those without the snow covering that can be predicted from the fit function.

Journal Articles

Deposition of radiocesium on the river flood plains around Fukushima

Saegusa, Hiromitsu; Oyama, Takuya; Iijima, Kazuki; Onoe, Hironori; Takeuchi, Ryuji; Hagiwara, Hiroki

Journal of Environmental Radioactivity, 164, p.36 - 46, 2016/11

 Times Cited Count:13 Percentile:39.85(Environmental Sciences)

The environments of Fukushima have been contaminated due to the Fukushima Daiichi Nuclear Power Plant accidents caused by the Great East Japan Earthquake on March 11, 2011. Released radio-cesium mainly affects radiation dose in the environment of Fukushima. It is concerned that redistribution of the radiation dose due to water discharge will be occurred due to the transportation of radio-cesium. Especially, deposition of the transferred soil particle with radio-cesium at flood plain with downstream area is possible cause of increasing radiation dose. Therefore, it is important to understand the influence of deposition behavior of radio-cesium on radiation dose. The paper discusses the deposition behaviors of radio-cesium at river based on the data obtained from the river investigations.

Journal Articles

Survey and countermeasures on radiocesium inflow into a laboratory building for radioactivity analysis

Kurita, Yoshiyuki; Saegusa, Jun; Maeda, Satoshi

Nihon Hoshasen Anzen Kanri Gakkai-Shi, 15(2), p.180 - 185, 2016/11

In 2012, JAEA has established a laboratory in Fukushima-city to implement radioactivity analysis of environmental samples. Key nuclides measured in this laboratory are $$^{134}$$Cs and $$^{137}$$Cs (radiocesium). For the purpose, situation of radiocesium inflow into the laboratory building and its effects were investigated based on high-resolution gamma-spectrometry with germanium detectors. As a result, the surface density of radiocesium in the laboratory was found to be far below the minimum detectable activities of survey instruments routinely used for radiation control purposes.

Journal Articles

Radioactivity decontamination in and around school facilities in Fukushima

Saegusa, Jun; Tagawa, Akihiro; Kurikami, Hiroshi; Iijima, Kazuki; Yoshikawa, Hideki; Tokizawa, Takayuki; Nakayama, Shinichi; Ishida, Junichiro

Mechanical Engineering Journal (Internet), 3(3), p.15-00609_1 - 15-00609_7, 2016/06

After the Fukushima nuclear accident, JAEA lead off demonstration tests to find out effective decontamination methods for various school facilities in Fukushima. It included (1) dose reduction measures at schoolyards, (2) purification of swimming pool water and (3) removal of surface contamination of playground equipments. Through these tests, they established practical methods suitable for each situation; (1) At school yards, dose rates were drastically reduced by removing topsoil which was then placed in trenches of 1 m deep; (2) For the purification of pool water, the flocculation-coagulation treatment was found to be effective for collecting radiocesium dissolved in the water; (3) Demonstration tests for playground equipments, such as horizontal bars and a sandbox wood frame, suggested that effectiveness of decontamination considerably varied depending on the material, paint or coating condition. This paper reviews these demonstrations.

JAEA Reports

Project report on the construction phase at the Mizunami Underground Research Laboratory Project

Nohara, Tsuyoshi; Saegusa, Hiromitsu*; Iwatsuki, Teruki; Hama, Katsuhiro; Matsui, Hiroya; Mikake, Shinichiro; Takeuchi, Ryuji; Onoe, Hironori; Sasao, Eiji

JAEA-Research 2015-026, 98 Pages, 2016/03

JAEA-Research-2015-026.pdf:32.97MB

Tono Geoscience Center (TGC) of Japan Atomic Energy Agency (JAEA) is being performed Mizunami Underground Research Laboratory (MIU) Project, which is a broad scientific study of the deep geological environment as a basis of research and development for geological disposal of nuclear wastes, in order to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in fractured crystalline rock. The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The project goals of the MIU Project from Phase I through to Phase III are: (1) to establish techniques for investigation, analysis and assessment of the deep geological environment, and (2) to develop a range of engineering for deep underground application. This report summarizes the results of geoscientific study on Phase II to 500m depth. During Construction phase, we have evaluated of adequacy of techniques for investigation, analysis and assessment of the deep geological environment on Surface-based Investigation phase, and have established systematic methodology for stepwise investigation and evaluation of the geological environment on Construction phase. Further, with respect to design and construction of underground facilities, it was confirmed the validity of the engineering involved in the construction, maintenance and management of underground facilities.

JAEA Reports

Information collection regarding geoscientific monitoring techniques during closure of underground facility in crystalline rock

Hosoya, Shinichi*; Yamashita, Tadashi*; Iwatsuki, Teruki; Saegusa, Hiromitsu; Onoe, Hironori; Ishibashi, Masayuki

JAEA-Technology 2015-027, 128 Pages, 2016/01

JAEA-Technology-2015-027.pdf:33.66MB

The study for development of drift backfilling technologies is one of the critical issues in the Mizunami Underground Research Laboratory (MIU) project, and its purposes are to develop closure methodology and technology, and long-term monitoring technology, and to evaluate resilience of geological environment. To achieve the purposes, previous information from the case example of underground facility constructed in crystalline rock in Europe has been collected. In particular, the boundary conditions for the closure, geological characteristics, technical specifications, and method of monitoring have been focused. The information on the international project regarding drift closure test and development of monitoring technologies has also been collected. In addition, interviews were conducted to specialists who have experiences involving planning, construction management, monitoring, and safety assessment for the closure. Based on the collected information, concept and point of attention, which are regarding drift closure testing, and planning, execution management and monitoring on the closure of MIU, have been specified.

Journal Articles

Groundwater flow modeling in construction phase of the Mizunami Underground Research Laboratory project

Onoe, Hironori; Saegusa, Hiromitsu; Takeuchi, Ryuji

Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 72(1), p.13 - 26, 2016/01

AA2015-0210.pdf:4.75MB

The Japan Atomic Energy Agency is conducting the Mizunami Underground Research Laboratory (URL) project in Mizunami, Gifu, in order to establish scientific and technical basis for geological disposal of high-level radioactive waste. This paper comprehensively describes the result of groundwater flow modeling using data of hydraulic responses and hydrochemical changes due to URL construction. Technical know-how and methodology of hydrogeological monitoring and groundwater flow modeling were presented for characterization of hydraulic heterogeneities in fractured crystalline rock. Furthermore, effectivity of data acquisition of hydrochemical changes in groundwater for validation of result of groundwater flow modeling was indicated.

Journal Articles

Influence on groundwater flow conditions by groundwater pressure change induced by earthquakes; Case study of Tono Area

Takeuchi, Ryuji; Tsuyuguchi, Koji*; Onoe, Hironori; Saegusa, Hiromitsu*; Beppu, Shinji

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 22(2), p.37 - 52, 2015/12

Assessment of the geological environment for the long term safety of geological disposal systems for high-level radioactive waste requires consideration for any phenomenon resulting in cumulative change to the geological environment at the regional scale. Groundwater pressure changes induced by earthquakes, for example, are one of the phenomena to be considered. Groundwater pressure changes induced by earthquakes have been observed during long-term monitoring carried out by Japan Atomic Energy Agency in the Tono Area, Gifu. In this paper, the observations of groundwater pressure change induced by earthquakes are summarized. In addition, an impact on groundwater flow conditions induced by earthquakes is discussed. In order to evaluate the long-term stability of groundwater flow condition, it is important to focus not only the change of groundwater pressure by earthquakes but also the change of the hydraulic gradient and hydraulic permeability.

JAEA Reports

Mizunami Underground Research Laboratory Project, Annual report for fiscal year 2014

Hama, Katsuhiro; Mikake, Shinichiro; Ishibashi, Masayuki; Sasao, Eiji; Kuwabara, Kazumichi; Ueno, Tetsuro; Onuki, Kenji*; Beppu, Shinji; Onoe, Hironori; Takeuchi, Ryuji; et al.

JAEA-Review 2015-024, 122 Pages, 2015/11

JAEA-Review-2015-024.pdf:80.64MB

Japan Atomic Energy Agency (JAEA) at Tono Geoscience Center (TGC) is pursuing a geoscientific research and development project namely the Mizunami Underground Research Laboratory (MIU) Project in crystalline rock environment in order to construct scientific and technical basis for geological disposal of High-level Radioactive Waste (HLW). The MIU Project has three overlapping phases: Surface-based Investigation phase (Phase I), Construction phase (Phase II), and Operation phase (Phase III). The MIU Project has been ongoing the Phase III, as the Phase II was concluded for a moment with the completion of the excavation of horizontal tunnels at GL-500m level in February 2014. This report presents the results of the investigations, construction and collaboration studies in fiscal year 2014.

JAEA Reports

Mizunami Underground Research Laboratory Project, Plan for fiscal year 2015

Hama, Katsuhiro; Takeuchi, Ryuji; Saegusa, Hiromitsu; Iwatsuki, Teruki; Sasao, Eiji; Mikake, Shinichiro; Ikeda, Koki; Sato, Toshinori; Osawa, Hideaki; Koide, Kaoru

JAEA-Review 2015-021, 27 Pages, 2015/10

JAEA-Review-2015-021.pdf:4.35MB

The Mizunami Underground Research Laboratory (MIU) project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of geological disposal technologies through investigations of the deep geological environment in the crystalline host rock (granite rock) at Mizunami City in Gifu Prefecture, central Japan. This report summarizes the research and development activities planned for fiscal year 2015 based on the MIU Master Plan updated in 2015 and so on. On the occasion of the reform of the entire JAEA organization in 2014, JAEA identified the critical issues on the geoscientific research program: "Development of modelling technologies for mass transport", "Development of drift backfilling technologies" and "Development of technologies for reducing groundwater inflow", based on the latest results of the synthesizing R&D. Investigations on those critical issues will be performed at the MIU in fiscal year 2015.

JAEA Reports

Study for development of the methodology for multi-scale hydrogeological modeling taking into account hydraulic heterogeneity caused by fracture network

Saegusa, Hiromitsu; Onoe, Hironori; Ishibashi, Masayuki; Tanaka, Tatsuya*; Abumi, Kensho*; Hashimoto, Shuji*; Bruines, P.*

JAEA-Research 2015-011, 59 Pages, 2015/10

JAEA-Research-2015-011.pdf:49.44MB

It is important to evaluate groundwater flow characteristics on several spatial scales for assessment of long-term safety on geological disposal of high-level radioactive wastes. An estimation of hydraulic heterogeneity caused by fracture network is significant for evaluation of the groundwater flow characteristics in the region of tens of meters square. Heterogeneity of equivalent hydraulic properties is needed to estimate for evaluation of the groundwater flow characteristics in the region of several km square. In order to develop the methodology for multi-scale hydrogeological modeling taking into account the hydraulic heterogeneity, spatial distribution of fractures and their hydraulic properties have been modeled using discrete fracture network (DFN) model. Then, hydrogeological continuum model taking into account the hydraulic heterogeneity has been estimated based on the DFN model. Through this study, the methodology for multi-scale hydrogeological modeling according to type of investigation data has been proposed.

Journal Articles

Predictions of transmissivity of fault zones from strength-stress conditions of rocks

Ishii, Eiichi; Matsuoka, Toshiyuki; Saegusa, Hiromitsu; Takeuchi, Ryuji

Nihon Oyo Chishitsu Gakkai Heisei-27-Nendo Kenkyu Happyokai Koen Rombunshu, p.135 - 136, 2015/09

no abstracts in English

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