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Nakayama, Masashi; Tanai, Kenji
JAEA-Review 2019-032, 32 Pages, 2020/02
JAEA-Review-2019-032.pdf:1.84MB
There are various types of monitoring in the geological disposal of high-level radioactive waste, such as monitoring for confirmation of construction quality and the status of engineered barrier, and monitoring to help manage construction, operation and closure activities, etc. Among these monitoring methods, monitoring related to the confirmation of the state of engineered barrier has been studied in international joint research on monitoring concepts and specific methods. Since monitoring equipment is affected by temperature, humidity, pressure, radiation, water quality, etc., it is important to consider geological environmental conditions and radiation effects. This report compares the radiation resistance of the materials used in the monitoring equipment with the absorbed dose in the buffer material obtained by analysis, and qualitatively examines the effects of radiation on the monitoring equipment. As a result of the examination, it was estimated that the dose did not affect the monitoring equipment. However, it is necessary to verify the possibility of reliable data acquisition by irradiation tests for monitoring devices with built-in electronic components.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2019-029, 36 Pages, 2020/02
JAEA-Review-2019-029.pdf:2.33MB
JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 "Development of Gel Filler that Facilitates Fuel Debris Retrieval". When gel materials such as polymer, silicate and clay minerals with adjusted viscosity are used in the process of debris retrieval, the gel would not leak down from the damaged parts, resulting in the reduction of surrounding air dose rate. In addition, gel materials can reduce the diffusion and scattering of dust that is produced by cutting. For these reasons, we propose a method where inside of a containment vessel is filled by gel materials in order to simplify the debris retrieval.
Abe, Hironobu; Hatakeyama, Nobuya; Yamazaki, Masanao; Okuzono, Akihiko*; Sakai, Tetsuo*; Inoue, Masahiro*
JAEA-Research 2009-019, 192 Pages, 2020/02
JAEA-Research-2009-019.pdf:8.07MB
Construction of the underground facility is on going at the Horonobe Underground Research Center, a division of the Japan Atomic Energy Agency. The facility is consisted of three shafts and horizontal drifts at the completion of construction and it is excavated in geological environment with methane gas, so it is important to secure the workers and visitors security in case of fire in the underground. However, it is known that the fire gas such as methane shows a complicated behavior by drift effect and so on and very difficult to predict its behavior, even if under enforced ventilation. In order to construct new prediction method of the fire gas behavior, the model scaled experiments were conducted by using the basic model which consists of shafts and drifts. As a results, fundamental data of the fire gas behavior was grasped and complicated behavior of the fire gas such as three-dimensional backflow and main flow inversion phenomena at the underground structure were ascertained. A new fire gas behavior analysis system has been designed and a prototype system has been programmed which is able to simulate the phenomena noted above. Coupling analysis method is adapted to the system, which consists of mainly one-dimensional ventilation network analysis and simplified computational fluid dynamics program named M-CFD. To minimize calculation time, M-CFD was designed as two-dimensional calculation with simulators multi area analysis system. Using the prototype system, several experimented models representing typical behavior of fire gas have been simulated for model scaled experiments. The system qualitatively reappeared the phenomena such as back flow or main flow inversion, and most of calculations completed in expected time. This indicates appropriateness of the prototype system, but some upgrade such as heat conductivity analysis in the wall rock mass transfer calculation, user friendly interface system and others will be required.
Tobita, Minoru*; Haraga, Tomoko; Sasaki, Takayuki*; Seki, Kotaro*; Omori, Hiroyuki*; Kochiyama, Mami; Shimomura, Yusuke; Ishimori, Kenichiro; Kameo, Yutaka
JAEA-Data/Code 2019-016, 72 Pages, 2020/02
JAEA-Data-Code-2019-016.pdf:2.67MB
In the future, radioactive wastes which generated from research and testing reactors in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. Therefore, it is required to establish the method to evaluate the radioactivity concentrations of radioactive wastes by the time it starts disposal. In order to contribute to this work, we collected and analyzed the samples generated from JRR-2, JRR-3 and Hot laboratory facilities. In this report, we summarized the radioactivity concentrations of 25 radionuclides (
H, 
C, 
Cl, 
Co, 
Ni, 
Sr, 
Nb, 
Mo, 
Tc, 
Ag, 
Sn, 
I, 
Cs, 
Eu, 
Eu, 
U, 
U, 
U, Pu, 
Pu, 
Pu, 
Pu, Am, 
Am, 
Cm) which were obtained from radiochemical analysis of those samples.
Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi
JAEA-Data/Code 2019-014, 56 Pages, 2020/02
JAEA-Data-Code-2019-014.pdf:6.56MB
JAEA-Data-Code-2019-014-appendix(CD-ROM).zip:5.81MB
Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Groundwater pressure and geochemical parameters such as pH and oxidation-reduction potential in the deep groundwater have been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the data of groundwater pressure which have been obtained by the monitoring systems installed at the 350 m gallery. The data obtained from April 1, 2016 until March 31, 2019 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.
Mitsukai, Akina; Haraga, Tomoko; Ishimori, Kenichiro; Kameo, Yutaka
JAEA-Data/Code 2019-012, 70 Pages, 2020/02
JAEA-Data-Code-2019-012.pdf:3.86MB
It is necessary to establish practical evaluation methods to determine radioactivity concentration of radioactive wastes which generated from research and testing reactors in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. Therefore, it is required to establish the method to evaluate the radioactivity concentrations of radioactive wastes by the time it starts disposal. In order to contribute to this work, we collected and analyzed the samples generated from Post Irradiation Examination Facility. In this report, we summarized the radioactivity concentrations of 19 radionuclides which were obtained from radiochemical analysis of those samples.
Kaburagi, Masaaki; Torii, Tatsuo; Ogawa, Toru
JAEA-Review 2019-031, 251 Pages, 2020/01
JAEA-Review-2019-031.pdf:57.36MB
There is high expectation for advanced remote technology and robotics to reduce the radiation exposure for workers in harsh nuclear environments such as the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). However, the radiation tolerance of state-of-the-art key components, sensors and electronic devices, for remote operation is still limited. In order to extend the application of robotics in nuclear energy, it is pertinent to develop "Radiation hardness" of components and "Radiation smartness" in operation procedures. Furthermore, developments of "Radiation measurement" and "Technology to recognize the location and to grasp the surrounding environment", including the radiation imaging of the high dose-rate fields inside the FDNPS and the detection of nuclear fuel debris, are necessary for the future nuclear fuel debris retrieval. This Fukushima Research Conference aims to share the future vision for advancing the remote technology among experts from diverse fields.
Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*
JAEA-Review 2019-027, 70 Pages, 2020/01
JAEA-Review-2019-027.pdf:5.18MB
JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 "Development of Technology for Rapid Analysis of Strontium-90 with Low Isotopic Abundance Using Laser Resonance Ionization". In this study, we will develop a rapid analysis technique for strontium-90 using diode laser-based resonance ionization with elemental and isotopic selectivity. Strontium-90 is one of the major difficult-to-measure nuclides released into the environment due to the accident at Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi Nuclear Power Station. Our method is particularly intended for real samples which contain high concentrations of strontium stable isotopes such as marine samples.
Collaborative Laboratories for Advanced Decommissioning Science; Tokyo Institute of Technology*
JAEA-Review 2019-026, 51 Pages, 2020/01
JAEA-Review-2019-026.pdf:2.8MB
JAEA/CLADS had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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. Among the adopted proposals in FY2018, this report summarizes the research results of the "Establishment of Measurement System for Radiation-dependent Mutation in Organ Tissue Cells Derived from Human iPS Cells". The purpose of the present study is to establish an experimental system to evaluate the difference in radiation-dependent mutation among tissues. In previous studies, unified evaluation of the difference in radiation-dependent mutation among tissues has been difficult because the mutation rate among tissues had been evaluated using cell lines taken from different individuals. Recent biotechnological innovation in stem cell field represented by iPS cells has become enable to induce differentiation of tissue cells from a single cell. In the present study, Tokyo Institute of Technology produce tissue cells in nervous, dermal, blood and circulatory systems by unifying these new technologies. Using these tissue cells, we measure the mutation rate for each tissue after the radiation exposure, and aim to establish an experimental system to evaluate the difference in mutation depending on tissues by constructing a mathematical model.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2019-025, 36 Pages, 2020/01
JAEA-Review-2019-025.pdf:2.57MB
CLADS, JAEA, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 "Development of Technology to Simultaneously Measure Viscosity and Surface Tension of Molten Materials in Reactor Core". Since (U,Zr)O
and boride, molten materials in reactor core, exist at extremely high temperature, chemical reactions between the vessel and these molten materials are unavoidable. Therefore, it is difficult to measure the thermophysical property of these materials. In the present study, droplets are produced by heating and melting the samples levitated by a gas levitation method, then the droplets are collided with a substrate. From the instant behavior of the collision, a new technology to simultaneously derive the viscosity and surface tension will be developed.
Collaborative Laboratories for Advanced Decommissioning Science; Okayama University*
JAEA-Review 2019-024, 61 Pages, 2020/01
JAEA-Review-2019-024.pdf:2.22MB
CLADS, JAEA, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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". In the present study, the effect of alpha-ray emission in human body on the surrounding cells is estimated, and biological response to alpha-ray exposure is investigated at the whole organism level, by the evaluation method for radiation effects using radon that is an alpha-ray emitting nuclide, because there have been extensive studies on radon so far. From the obtained results, a model to evaluate the effect of internal exposure by alpha-ray emitting nuclides on health is constructed. Through these studies, we aim to form a research base by the interdisciplinary organic collaboration among research organizations.
Collaborative Laboratories for Advanced Decommissioning Science; University of Tsukuba*
JAEA-Review 2019-023, 33 Pages, 2020/01
JAEA-Review-2019-023.pdf:1.97MB
CLADS, JAEA, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 'Upgrading of Recovery Method for Radioactive Microparticles by Heavy Liquid Separation Aiming to Volume Reduction of Contaminated Soil'. After the accident of the Fukushima Daiichi Nuclear Power Station, radioactive cesium has been heterogeneously distributed in surface soil due to the existence of radioactive microparticles and clay minerals. Therefore, the selective removal of these microparticles will lead to the volume reduction of contaminated soil. The present study examines methods for selectively removing radioactive microparticles from soil. Also, in order to reduce the volume of contaminated soil, we search a possibility to practically apply the separation method that uses the difference in specific gravity of particles (heavy liquid separation method).
Collaborative Laboratories for Advanced Decommissioning Science; Tokyo Polytechnic University*
JAEA-Review 2019-022, 35 Pages, 2020/01
JAEA-Review-2019-022.pdf:2.71MB
CLADS, JAEA, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. 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 Development of Semantic Survey Map Building System Using Semi-autonomous Mobile Robots for Surveying of Disaster Area and Gathering of Information in Nuclear Power Station. The objective of the present study is to research and develop semi-autonomous mobile robot systems (multi-sensor fusion system, semantic simultaneous localization and mapping (SLAM), system for traversable-route learning and safe traversable-route presentation, etc.) that simply, safely, and rapidly make semantic survey maps including multiple information (air dose rate, temperature, obstacles, etc.). The system will be applied to the investigation of the situation inside the building of the nuclear power station where people cannot access at the time of disaster.
Saiga, Atsushi
JAEA-Review 2019-018, 122 Pages, 2020/01
JAEA-Review-2019-018.pdf:10.52MB
The Horonobe Underground Research Laboratory Project is planned to extend over a period 20 years. The investigations will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction Phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). This report summarizes the results of the investigations for the 2018 fiscal year (2018/2019). The investigations, which are composed of "Geoscientific research" and "R&D on geological disposal technology", were carried out according to "Horonobe Underground Research Laboratory Project Investigation Program for the 2018 fiscal year". The results of these investigations, along with the results which were obtained in other departments of Japan Atomic Energy Agency (JAEA), are properly offered to the implementations and the safety regulations. For the sake of this, JAEA has proceeded with the project in collaboration with experts from domestic and overseas research organizations.
HPC Technology Promotion Office*
JAEA-Review 2019-017, 182 Pages, 2020/01
JAEA-Review-2019-017.pdf:11.11MB
Japan Atomic Energy Agency (JAEA) conducts research and development (R&D) in various fields related to nuclear power as a comprehensive institution of nuclear energy R&Ds, and utilizes computational science and technology in many activities. As shown in the fact that about 20 percent of papers published by JAEA are concerned with R&D using computational science, the supercomputer system of JAEA has become an important infrastructure to support computational science and technology. In FY2018, the system was used for R&D aiming to restore Fukushima (environmental recovery and nuclear installation decommissioning) as a priority issue, as well as for JAEA's major projects such as research and development of fast reactor cycle technology, research for safety improvement in the field of nuclear energy, and basic nuclear science and engineering research. This report presents a great number of R&D results accomplished by using the system in FY2018, as well as user support, operational records and overviews of the system, and so on.
Geological Disposal Research and Development Department
JAEA-Evaluation 2019-010, 69 Pages, 2020/01
JAEA-Evaluation-2019-010.pdf:2.54MBJAEA-Evaluation-2019-010-appendix(CD-ROM).zip:13.88MB
Japan Atomic Energy Agency (JAEA) consulted the advisory committee, "Evaluation Committee on Research and Development (R&D) Activities for Geological Disposal of High-Level Radioactive Waste", for an interim review of R&D activities on high-level radioactive waste disposal in accordance with "General Guideline for the Evaluation of Government Research and Development (R&D) Activities" by the Cabinet Office, Government of Japan, "Guideline for Evaluation of R&D in Ministry of Education, Culture, Sports, Science and Technology" and JAEA's "Regulation on Conduct for Evaluation of R&D Activities". In response to JAEA's request, the Committee reviewed mainly the progress of the R&D project on geological disposal, the relevance of the project outcome during the period of FY2015-2018. This report summarizes the results of the assessment by the Committee with the Committee report attached.
Aihara, Jun; Goto, Minoru; Ueta, Shohei; Tachibana, Yukio
JAEA-Data/Code 2019-018, 22 Pages, 2020/01
JAEA-Data-Code-2019-018.pdf:1.39MB
Concept of Pu-burner high temperature gas-cooled reactor (HTGR) was proposed for purpose of more safely reducing amount of recovered Pu. In Pu-burner HTGR concept, coated fuel particle (CFP), with ZrC coated yttria stabilized zirconia (YSZ) containing PuO (PuO-YSZ) small particle and with tri-structural isotropic (TRISO) coating, is employed for very high burn-up and high nuclear proliferation resistance. ZrC layer is oxygen getter. On the other hand, we have developed Code-B-2.5.2 for prediction of pressure vessel failure probabilities of SiC-tri-isotropic (TRISO) coated fuel particles for HTGRs under operation by modification of an existing code, Code-B-2. The main purpose of modification is preparation of applying code for CFPs of Pu-burner HTGR. In this report, basic formulae are described.
Morita, Yasuji; Tsubata, Yasuhiro
JAEA-Data/Code 2019-015, 45 Pages, 2020/01
JAEA-Data-Code-2019-015.pdf:2.09MB
Decay heat from radioactive elements in high-level liquid waste (HLLW) and separated solutions in partitioning process was evaluated as a basic data for safety assessment of partitioning process. In the evaluation of HLLW from spent UO fuel burned-up to 45 GWd/t in light water reactor, decay heat value from fission products decreased as the cooling period become longer but heat from actinides, Am and Cm, was almost constant until 50-year cooling. Decay heat density in solutions of Am, Cm and rare earth elements and of Am and Cm without concentration for volume reduction does not exceed the heat density of HLLW, but the concentration should be required to minimize the scale of the partitioning process. Separated solution of Am and Cm must be concentrated to convert the two elements to a solid state to make fuel for transmutation, and the decay heat density of the concentrated solution of Am and Cm is 10 times higher compared with the Pu solution of same element concentration. Higher burn-up UO fuel and MOX fuel in light water reactor and minor-actinide-recycled MOX fuel in fast reactor were also considered and the evaluated decay heat was compared among the spent fuels.
Miyara, Nobukatsu; Matsuoka, Toshiyuki
JAEA-Data/Code 2019-013, 8 Pages, 2020/01
JAEA-Data-Code-2019-013.pdf:1.45MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)1.zip:239.91MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)10.zip:346.69MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)11.zip:237.95MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)12.zip:335.05MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)13.zip:335.0MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)2.zip:433.26MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)3.zip:360.88MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)4.zip:292.24MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)5.zip:315.31MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)6.zip:426.42MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)7.zip:286.49MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)8.zip:187.61MBJAEA-Data-Code-2019-013-appendix(DVD-ROM)9.zip:826.1MB
As part of the research and development program on the geological disposal of high-level radioactive waste (HLW), the Horonobe Underground Research Center, a division of the Japan Atomic Energy Agency (JAEA), is implementing the Horonobe Underground Research Laboratory Project (Horonobe URL Project) with the aim at investigating sedimentary rock formations. This data collection is a compilation of Earthquake observation data acquired in the Horonobe Underground Research Project (Phase II).
Sugino, Kazuteru; Takino, Kazuo
JAEA-Data/Code 2019-011, 110 Pages, 2020/01
JAEA-Data-Code-2019-011.pdf:3.37MB
A deterministic discrete ordinates method (SN method) transport calculation code for three-dimensional hexagonal geometry has been developed as the MINISTRI code (Ver. 7.0). MINISTRI is based on the triangle-mesh finite difference method, which can perform neutron transport calculations with high accuracy for cores of fast power reactors and assemblies of the Russian BFS critical facility. The present study has derived a proper scheme for remarkably improving the convergence of MINISTRI by investigating the issue of previous MINISTRI (Ver. 1.1), which sometimes plays a poor convergence performance in calculations for large-scale power reactor cores. The verification test of improved MINISTRI has been carried out for various cores by setting the reference result as the multi-group Monte-Carlo calculation with the same cross-sections as used in MINISTRI. As a result, it is found that the agreements are within 0.1% for eigenvalues and within 0.7% for power distributions. Thus, the satisfying accuracy of MINISTRI has been confirmed. In order to reduce the calculation time, the initial diffusion calculation scheme and the parallel processing have been implemented. As a result, the calculation time is reduced to the approximately one tenth compared with previous MINISTRI. Furthermore, adoption of the treatment of the anisotropic cell streaming effect, preparation of the perturbation calculation tool, implementation of the function for specification of the triangle-mesh-wise material and merging of the hexagonal-mesh calculation code MINIHEX have been carried out. Thus, the versatility of MINISTRI has been enhanced.