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Journal Articles

Identification of carbon in glassy cesium-bearing microparticles using electron microscopy and formation mechanisms of the microparticles

Hidaka, Akihide

Nuclear Technology, 208(2), p.318 - 334, 2022/02

 Times Cited Count:0 Percentile:0.01(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.

JAEA Reports

Development of methodology combining chemical analysis technology with informatics technology to understand perspectives property of debris and tie-up style human resource development (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Fukushima University*

JAEA-Review 2021-035, 89 Pages, 2021/12

JAEA-Review-2021-035.pdf:6.37MB

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 "Development of methodology combining chemical analysis technology with informatics technology to understand perspectives property of debris and tie-up style human resource development" conducted in FY2020. The present study aims to Goal of this study is to implement a research plan relate to a development of combinational technology of new chemical analysis with informatics, and the aim is to develop new system for whole image estimation system using small quantities of information. Conducting the collaboration study with JAEA researchers (tie-up style) make connect to the development of human resource from master's course student to post-doctoral researchers who are progress in the local-based and/or many academics

JAEA Reports

Estimation of the in-depth debris status of Fukushima Unit-2 and Unit-3 with Multi-physics modeling (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Waseda University*

JAEA-Review 2021-034, 107 Pages, 2021/12

JAEA-Review-2021-034.pdf:6.08MB

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 (1F), 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 "Estimation of the in-depth debris status of Fukushima Unit-2 and Unit-3 with multi-physics modeling" conducted in FY2020. Continuous update on understanding of the damaged 1F reactors is important for safe and efficient decommissioning of the reactors. This study aims to estimate the in-depth debris status of the damaged 1F Unit-2 and Unit-3 through multi-physics modeling, which comprises of MPS method, simulated molten debris relocation experiment and high-temperature melt property data acquisition in the three-year project from FY2019.

Journal Articles

Revaporization behavior of cesium and iodine compounds from their deposits in the steam-boron atmosphere

Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Gou$"e$llo, M.*

ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12

Journal Articles

Validation of ATDMs at early after the lF accident using air dose rate estimated by airborne concentration and surface deposition density

Moriguchi, Yuichi*; Sato, Yosuke*; Morino, Yu*; Goto, Daisuke*; Sekiyama, Tsuyoshi*; Terada, Hiroaki; Takigawa, Masayuki*; Tsuruta, Haruo*; Yamazawa, Hiromi*

KEK Proceedings 2021-2, p.21 - 27, 2021/12

no abstracts in English

Journal Articles

Evaluation of fixed absorber reactivity measurement in the prototype fast reactor Monju

Ohgama, Kazuya; Katagiri, Hiroki; Takegoshi, Atsushi*; Hazama, Taira

Nuclear Technology, 207(12), p.1810 - 1820, 2021/12

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

Journal Articles

Tree cutting approach for domain partitioning on forest-of-octrees-based block-structured static adaptive mesh refinement with lattice Boltzmann method

Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki

Parallel Computing, 108, p.102851_1 - 102851_12, 2021/12

The aerodynamics simulation code based on the lattice Boltzmann method (LBM) using forest-of-octrees-based block-structured local mesh refinement (LMR) was implemented, and its performance was evaluated on GPU-based supercomputers. We found that the conventional Space-Filling-Curve-based (SFC) domain partitioning algorithm results in costly halo communication in our aerodynamics simulations. Our new tree cutting approach improved the locality and the topology of the partitioned sub-domains and reduced the communication cost to one-third or one-fourth of the original SFC approach. In the strong scaling test, the code achieved maximum $$times1.82$$ speedup at the performance of 2207 MLUPS (mega- lattice update per second) on 128 GPUs. In the weak scaling test, the code achieved 9620 MLUPS at 128 GPUs with 4.473 billion grid points, while the parallel efficiency was 93.4% from 8 to 128 GPUs.

Journal Articles

Influence of distant scatterer on air kerma measurement in the evaluation of diagnostic X-rays using Monte Carlo simulation

Tominaga, Masahide*; Nagayasu, Yukari*; Sasaki, Motoharu*; Furuta, Takuya; Hayashi, Hiroaki*; Oita, Masataka*; Nishiyama, Yuichi*; Haga, Akihiro*

Radiological Physics and Technology, 14(4), p.381 - 389, 2021/12

Due to recent advance of diagnostic radiology, the increase of diagnostic radiation exposure to patient becomes problem. Diagnostic Reference Levels has been released to optimized the radiation exposure to patients in Japan recently. The evaluation of entrance surface dose (ESD) is recommended to assess the dose level for general X-ray examination. The ESD can be easily evaluated by multiplying the backscatter factor of the patient body on the free-in-air air kerma. The air kerma free-in-air value used to estimate ESD may contain X-rays scattered from obstacles located at the time of measurement, which may induce non-minor error in assessments. We therefore studied the influence of scattered X-rays on air kerma measurement under various environments (distances, field sizes, and materials). It was found that the dependence on the X-ray energy and field size was different for different materials. The X-ray contamination can be ignored for all the materials when the distance to the scatterer exceeds 35 cm.

JAEA Reports

Report of the design examination and the installation work for the radiation shield at the beam injection area in the 3 GeV synchrotron

Nakanoya, Takamitsu; Kamiya, Junichiro; Yoshimoto, Masahiro; Takayanagi, Tomohiro; Tani, Norio; Kotoku, Hirofumi*; Horino, Koki*; Yanagibashi, Toru*; Takeda, Osamu*; Yamamoto, Kazami

JAEA-Technology 2021-019, 105 Pages, 2021/11

JAEA-Technology-2021-019.pdf:10.25MB

Since a user operation startup, the 3 GeV synchrotron accelerator (Rapid-Cycling Synchrotron: RCS) gradually reinforced the beam power. As a result, the surface dose rate of the apparatus located at the beam injection area of the RCS, such as the magnet, vacuum chambers, beam monitors, etc., increases year by year. The beam injection area has many apparatuses which required manual maintenance, so reducing worker's dose is a serious issue. To solve this problem, we have organized a task force for the installation of the shield. The task force has aimed to optimize the structure of the radiation shield, construct the installation procedure with due consideration of the worker's dose suppression. As the examination result of the shield design, we have decided to adopt removal shielding that could be installed quickly and easily when needed. We carried out shield installation work during the 2020 summer maintenance period. The renewal work required to install the shielding has been carried out in a under high-dose environment. For this reason, reducing the dose of workers was an important issue. So, we carefully prepared the work plan and work procedure in advance. During the work period, we implemented various dose reduction measures and managed individual dose carefully. As a result, the dose of all workers could be kept below the predetermined management value. We had installed removal shielding at the beam injection area in the 2020 summer maintenance period. We confirmed that this shield can contribute to the reduction of the dose during work near the beam injection area. It was a large-scale work to occupy the beam injection area during almost of the summer maintenance period. However, it is considered very meaningful for dose suppression in future maintenance works.

JAEA Reports

Interdisciplinary evaluation of biological effect of internal exposure by inhaling alpha-ray emitting nuclides represented by radon (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Okayama University*

JAEA-Review 2021-028, 57 Pages, 2021/11

JAEA-Review-2021-028.pdf:1.94MB

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 FY2018, this report summarizes the research results of the "Interdisciplinary evaluation of biological effect of internal exposure by inhaling alpha-ray emitting nuclides represented by radon" conducted from FY2018 to FY2020. Since the final year of this proposal was FY2020, the results for three fiscal years were summarized. The present study aims to evaluate the influence of radiation exposure to alpha-ray emitting dusts generated in decommissioning of the nuclear reactors. Radon is used here as a surrogate nuclide because it is an alpha-ray emitter and there have been extensive studies on it so far. The effect of alpha-ray emitted from a certain cell on its surrounding cells is estimated, and also biological response to alpha-ray exposure is investigated at the tissue and

Journal Articles

Comparisons between passive RCCSS on degree of passive safety features against accidental conditions and methodology to determine structural thickness of scaled-down heat removal test facilities

Takamatsu, Kuniyoshi; Matsumoto, Tatsuya*; Liu, W.*; Morita, Koji*

Annals of Nuclear Energy, 162, p.108512_1 - 108512_10, 2021/11

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

The objectives of this study are as follows: to understand the characteristics, degree of passive safety features for heat removal were compared for RCCSs based on atmospheric radiation and based on atmospheric natural circulation under the same conditions. Next, simulations on accidental conditions, such as increasing average heat-transfer coefficient via natural convection due to natural disasters, were performed with STAR-CCM+, and methodology to control the amount of heat removal was discussed. As a result, a new RCCS based on atmospheric radiation is recommended because of the excellent degree of passive safety features/conditions, and the amount of heat removal by heat transfer surfaces which can be controlled. Finally, methodology to determine structural thickness of scaled-down heat removal test facilities for reproducing natural convection and radiation was developed, and experimental methods by using pressurized and decompressed chambers was also proposed.

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.

JAEA Reports

Re-examinations of MA fuel composition for accelerator-driven system and its heat removal

Sugawara, Takanori; Moriguchi, Daisuke*; Ban, Yasutoshi; Tsubata, Yasuhiro; Takano, Masahide; Nishihara, Kenji

JAEA-Research 2021-008, 63 Pages, 2021/10

JAEA-Research-2021-008.pdf:4.43MB

This study aims to perform the neutronics calculations for accelerator-driven system (ADS) with a new fuel composition based on the SELECT process developed by Japan Atomic Energy Agency because the previous studies had used the ideal MA (minor actinide) fuel composition without uranium and rare earth elements. Through the neutronics calculations, it is shown that two calculation cases, with/without neptunium, satisfy the design criteria. Although the new fuel composition includes uranium and rare earth elements, the ADS core with the new fuel composition is feasible and consistent with the partitioning and transmutation (P&T) cycle. Based on the new fuel composition, the heat removal during fuel powder storage and fuel assembly assembling is evaluated. For the fuel powder storage, it is found that a cylindrical tube container with a length of 500 [mm] and a diameter of 11 - 21 [mm] should be stored under water. For the fuel assembly assembling, CFD analysis indicates that the cladding tube temperature would satisfy the criterion if the inlet velocity of air is larger than 0.5 [m/s]. Through these studies, the new fuel composition which is consistent with the P&T cycle is obtained and the heat removal with the latest conditions is investigated. It is also shown that the new fuel composition can be practically handled with respect to heat generation, which is one of the most difficult points in handling MA fuel.

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

Fast fault recovery scenarios for the JAEA-ADS linac

Yee-Rendon, B.; Tamura, Jun; Kondo, Yasuhiro; Nakano, Keita; Takei, Hayanori; Maekawa, Fujio; Meigo, Shinichiro

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.61 - 65, 2021/10

Japan Atomic Energy Agency (JAEA) is designing a 30 MW CW superconducting proton linac as a major component for the accelerator-driven subcritical system (ADS) project. The main challenge of the linac operation is the high reliability required to suppress thermal stress in the subcritical reactor. To this end, we implemented fault compensation schemes to enable a fast beam recovery; consequently, reducing the beam trip duration. This work presents strategies to increase the fault-tolerance capacity of the JAEA-ADS linac.

Journal Articles

Radiation shielding installation for beam injection section of 3GeV synchrotron

Nakanoya, Takamitsu; Kamiya, Junichiro; Yoshimoto, Masahiro; Takayanagi, Tomohiro; Tani, Norio; Kotoku, Hirofumi*; Horino, Koki*; Yanagibashi, Toru*; Takeda, Osamu*; Yamamoto, Kazami

Proceedings of 18th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.238 - 242, 2021/10

Since a user operation startup, the 3GeV synchrotron accelerator (Rapid-Cycling Synchrotron: RCS) gradually reinforced the beam power. As a result, the surface dose rate of the apparatus located at the beam injection area of the RCS increases year by year. The beam injection area has many apparatuses which required manual maintenance, so reducing worker's dose is a serious issue. To solve this problem, we have decided to adopt removal shielding that could be installed quickly and easily when needed. We carried out shield installation work during the 2020 summer maintenance period. The installation work of the shield has been carried out in a under high-dose environment. For this reason, reducing the dose of workers was an important issue. So, we carefully prepared the work plan and work procedure in advance. During the work period, we implemented various dose reduction measures and managed individual dose carefully. As a result, the dose of all workers could be kept below the predetermined management value. We had installed removal shielding at the beam injection area in the 2020 summer maintenance period. We confirmed that this shield can contribute to the reduction of the dose during work near the beam injection area.

Journal Articles

Formation of Type A glassy cesium-bearing microparticles from HEPA filter materials in Unit 3 during Fukushima Dai-ichi NPS accident; From viewpoint of similarity in silicate glass composition

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.

Journal Articles

Implications of the $$Z_{cs}$$(3985) and $$Z_{cs}$$(4000) as two different states

Meng, L.*; Wang, B.*; Wang, G.-J.*; Zhu, S.-L.*

Science Bulletin, 66(20), p.2065 - 2071, 2021/10

 Times Cited Count:0 Percentile:0.01(Multidisciplinary Sciences)

Two recently found tetraquark resonances $$Z_{cs}$$(3985) and $$Z_{cs}$$(4000) are studied in a solvable nonrelativistic effective field theory. We include the possible violations of heavy quark spin symmetry and SU(3) flavor symmetry in a comprehensive approach. Our results show that the decay rates can be used to judge whether these resonances can be different states or not.

Journal Articles

How the Cesium-bearing microparticles were generated?; Inference of an interdiscipinary researcher

Hidaka, Akihide

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 63(9), p.679 - 680, 2021/09

no abstracts in English

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