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Katsumura, Kosuke*; Takagi, Junichi*; Hosomi, Kenji*; Miyahara, Naoya*; Koma, Yoshikazu; Imoto, Jumpei; Karasawa, Hidetoshi; Miwa, Shuhei; Shiotsu, Hiroyuki; Hidaka, Akihide*; et al.
Nihon Genshiryoku Gakkai-Shi ATOMO
, 65(11), p.674 - 679, 2023/11
no abstracts in English
Hidaka, Akihide; Kawashima, Shigeto*; Kajino, Mizuo*
Journal of Nuclear Science and Technology, 60(7), p.743 - 758, 2023/07
Times Cited Count：2 Percentile：54.24(Nuclear Science & Technology)An accurate estimation of radionuclides released during the Fukushima accident is essential. Therefore, authors investigated Te release using the Unit emission-regression estimation method, in which the deposition distribution is weighted based on the hourly deposition obtained from mesoscale meteorological model calculations assuming Unit emissions. The previous study focused on confirming the applicability of this method. Subsequent examination revealed that if any part of the time when a release have occurred is missing from the estimated release period, the entire source term calculation will be distorted. Therefore, this study performed the recalculation by extending the estimation period to cover all major releases. Consequently, unspecified release events were clarified, and their correspondence to in-core events was confirmed. The 
Te release caused by Zr cladding complete oxidation can explain the regional dependence of the Te/
Cs ratio in the soil contamination map.
Hidaka, Akihide
Journal of Radioanalytical and Nuclear Chemistry, 332(6), p.1607 - 1623, 2023/03
Times Cited Count：0 Percentile：0.00(Chemistry, Analytical)no abstracts in English
Hagiwara, Hiroki; Kondo, Keietsu; Hidaka, Akihide
Journal of Radioanalytical and Nuclear Chemistry, 331(12), p.5905 - 5914, 2022/12
Times Cited Count：3 Percentile：47.03(Chemistry, Analytical)Hidaka, Akihide
Nuclear Technology, 208(2), p.318 - 334, 2022/02
Times Cited Count：6 Percentile：59.46(Nuclear Science & Technology)The author previously proposed that the Cs bearing microparticle (Type A) may have been formed by melting and atomization of glass fibers (GF) of the HEPA filter in the SGTS due to flame and blast during the hydrogen explosion in Unit 3. If this hypothesis is correct, the Type A could contain or accompany carbon (C), that ignites spontaneously above 623 K, because of the limited time to be heated up, inclusion of C in the binder applied on the GF surface and closely located charcoal filter. As the previous studies did not focus on C, the present analyses were performed with EPMA whether the Type A contains C. The results showed that the Type A contained C originating from the binder, and non-spherical particles accompanied by the Type A and the film surrounding the Type A contained more C, which is thought to originate from the charcoal filter. These results cannot be explained by the other mechanisms proposed so far, and can be explained consistently by the author proposed hypothesis.
C absorber material on melt progression and chemical forms of iodine or cesium under severe accident conditionsHidaka, Akihide
Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.341 - 356, 2021/10
Hidaka, Akihide
Proceedings of 2021 International Congress on Advances in Nuclear Power Plants (ICAPP 2021) (USB Flash Drive), 10 Pages, 2021/10
Author recently proposed that the Type A glassy Cesium-bearing microparticles that were released during the Fukushima accident may have been formed by melting and atomization of glass fibers of the High Efficiency Particulate Air (HEPA) filter in the Stand-by Gas Treatment System (SGTS) line in Unit 3 during the hydrogen explosion. In the present study, the components of the Type A and glass fibers of HEPA filter were examined using EPMA. The results showed that the components of the Type A were almost the same as that of the glass fibers except for Cs, Fe, Sn, which are considered to have been contained in the in-vessel-derived particles. When the glass fiber was irradiated with the electron beam of the Electron Probe Micro Analyzer (EPMA) under vacuum condition, spherical particles of a few micro m size were formed that looked very similar to the Type A. These strongly suggest that the HEPA filter is Si source of the Type A.
Hidaka, Akihide
Nihon Genshiryoku Gakkai-Shi ATOMO, 63(9), p.679 - 680, 2021/09
no abstracts in English
Hidaka, Akihide
Fission Product Behavior under Severe Accident, p.85 - 88, 2021/05
no abstracts in English
Liu, J.; Miyahara, Naoya; Miwa, Shuhei; Takano, Masahide; Hidaka, Akihide; Osaka, Masahiko
Journal of Nuclear Materials, 527, p.151819_1 - 151819_7, 2019/12
Times Cited Count：2 Percentile：18.28(Materials Science, Multidisciplinary)To evaluate the effect of each constituent element on the evaporation rate of ruthenium (Ru) from fission-produced alloy precipitates, the oxidation and evaporation behaviors of metallic Ru, molybdenum (Mo), palladium (Pd), rhodium (Rh) and Mo-Ru-Pd-Rh alloy powders were investigated by thermogravimetric analysis under oxidizing atmospheres from 1473 to 1723 K. The findings led to the following conclusions: (1) The quick oxidation of Mo into condensed Mo oxides can effectively suppress the oxidation and evaporation of Ru in alloy powders; (2) After the complete evaporation of Mo, the evaporation loss rate of Ru would be directly influenced by the Ru activity in the Ru-Pd-Rh alloys, which is determined by the composition of alloys.
Hidaka, Akihide
Journal of Nuclear Science and Technology, 56(9-10), p.831 - 841, 2019/09
Times Cited Count：12 Percentile：74.50(Nuclear Science & Technology)The insoluble Cs particles (Type A) were firstly observed in Tsukuba-city on the morning of March 15. The particles have been considered to be generated in RPV of Unit 2 by evaporation/condensation based on the measured 
Cs/Cs ratio and the core temperatures of each unit. However, the Type A particles with smaller diameter than the Type B particles of Unit 1 origin, are covered by almost pure silicate glass and have a trace of the quenching. This indicates that the particles could have been generated due to the melting of the HEPA filter in SGTS by the fire of H
detonation at Unit 3, and atomization followed by quenching of the molten materials by air blast of the explosion. Although the particles were mostly dispersed to the sea because of the wind direction, some of them deposited onto the lower elevation of R/B at Unit 3, could have been subsequently re-suspended and released into the environment, by the steam flow in the R/B caused by restart of the Unit 3 core cooling water injection at 2:30 of March 15.
Takahashi, Sentaro*; Kawashima, Shigeto*; Hidaka, Akihide; Tanaka, Sota*; Takahashi, Tomoyuki*
Nuclear Technology, 205(5), p.646 - 654, 2019/05
Times Cited Count：4 Percentile：35.53(Nuclear Science & Technology)Hidaka, Akihide; Himi, Masashi*; Addad, Y.*
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 4 Pages, 2019/05
no abstracts in English
Hidaka, Akihide
Genshiryoku No Ima To Ashita, p.264 - 265, 2019/03
no abstracts in English
Hidaka, Akihide; Yokoyama, Hiroya
Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2017 (AWC 2017) (USB Flash Drive), p.29 - 42, 2017/09
no abstracts in English
I and Cs releases during late phase of Fukushima Daiichi NPP accident by using I/Cs ratio of source terms evaluated reversely by WSPEEDI code with environmental monitoring data, J. Nucl. Sci. Technol. 2017, Corrected vertical axis of Figure 6Hidaka, Akihide; Yokoyama, Hiroya
Journal of Nuclear Science and Technology, 54(8), P. i, 2017/08
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)no abstracts in English
I and Cs releases during late phase of Fukushima Daiichi NPP accident by using I/Cs ratio of source terms evaluated reversely by WSPEEDI code with environmental monitoring dataHidaka, Akihide; Yokoyama, Hiroya
Journal of Nuclear Science and Technology, 54(8), p.819 - 829, 2017/08
Times Cited Count：13 Percentile：74.20(Nuclear Science & Technology)To clarify what happened during the Fukushima accident, the phenomena within RPV and the discussion of ties with the environmental monitoring are very important. However, the previous study has not necessarily advanced until the present that passed almost six years from the accident. The present study investigated I and Cs release behaviors during the late phase of the accident based on I/Cs ratio of the source terms that were recently evaluated backward by WSPEEDI code based on environmental monitoring data. The I release from the contaminated water in the basement of 1F2 and 1F3 reactor buildings was evaluated to be about 10% of I source term. The increase in Cs release from March 21 to 23 and from March 30 to 31 could be explained by the release of CsBO which is formed as a result of chemical reactions of Cs with BC due to re-ascension of the core temperature caused by slight shortage of the core cooling water.
Yamaguchi, Mika; Hidaka, Akihide; Ikuta, Yuko; Murakami, Kenta*; Tomita, Akira*; Hirose, Hiroya*; Watanebe, Masanori*; Ueda, Kinichi*; Namaizawa, Ken*; Onose, Takatoshi*; et al.
JAEA-Review 2017-002, 60 Pages, 2017/03
JAEA-Review-2017-002.pdf:9.41MB
Since 2010, IAEA has held the NEM School to develop future leaders who plan and manage nuclear energy utilization in their county. Since 2012, JAEA together with Japan Nuclear HRD Network, University of Tokyo, Japan Atomic Industrial Forum and JAIF International Cooperation Center have cohosted the school in Japan in cooperation with IAEA. Since then, the school has been held in Japan every year. In 2006, Japanese nuclear technology and experience, such as lessons learned from the Fukushima Daiichi Nuclear Power Plant accident, were provided to offer a unique opportunity for the participants to learn about particular cases in Japan. Through the school, we contributed to the internationalization of Japanese young nuclear professionals, development of nuclear human resource of other countries including nuclear newcomers, and enhanced cooperative relationship with IAEA. Additionally, collaborative relationship within the network was strengthened by organizing the school in Japan.
Hidaka, Akihide; Nakano, Yoshihiro; Watanabe, Yoko; Arai, Nobuyoshi; Sawada, Makoto; Kanaizuka, Seiichi*; Katogi, Aki; Shimada, Mayuka*; Ishikawa, Tomomi*; Ebine, Masako*; et al.
JAEA-Review 2016-011, 208 Pages, 2016/07
JAEA-Review-2016-011-01.pdf:33.85MBJAEA-Review-2016-011-02.pdf:27.68MB
JAEA has been conducting the Instructor Training Program (ITP) since 1996 under the auspices of MEXT to contribute to human resource development in currently 11 Asian countries in the field of radiation utilization for seeking peaceful use of nuclear energy. ITP consists of Instructor Training Course (ITC), Follow-up Training Course (FTC) and Nuclear Technology Seminars. In the ITP, trainings or seminars relating to technology for nuclear utilization are held in Japan by inviting nuclear related people from Asian countries to Japan and after that, the past trainees are supported during FTC by dispatching Japanese specialists to Asian countries. News Letter is also prepared to provide the broad range of information obtained through the trainings for local people near NPPs in Japan. The present report describes the activities of FY2014 ITP and future challenges for improving ITP more effectively.
Hidaka, Akihide
Enerugi Rebyu, 35(9), p.20 - 24, 2015/09
Operation of nuclear power plant causes accumulation of radionuclides in fuel rods as a result of nuclear fission of uranium and plutonium. During severe accidents, large amount of radionuclides are released from fuel and transport in the reactor coolant system and/or the containment. When the containment fails or its confinement function is lost, radionuclides could be released into the environment. Meanwhile, radionuclides can be removed by condensation onto wall, natural deposition such as gravitational settling, the engineered safety features (ESF) such as containment spray and so on. After various processes described above, the species, amounts and timing of radionuclide released into the environment is called source terms. The behavior of radionuclide can be described mechanistically by condensation or evaporation of gaseous radionuclide, deposition, growth and removal of aerosol by ESF. Present paper summarizes the radionuclide behavior during severe accidents.
