Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Ono, Hirokazu
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.140 - 143, 2024/12
In the geological disposal of high-level radioactive waste, after emplacement of an EBS, the near-field environment is affected by processes such as heat release from the waste, groundwater infiltration into the EBS, swelling and deformation of the buffer material, and chemical reactions between groundwater and minerals. It is crucial to develop simulation codes to evaluate such coupled thermal-hydraulic-stress-chemical (THMC) processes for safety assessment of geological disposal. The full-scale vertical-emplacement EBS experiment (Horonobe EBS experiment) has been undertaken in the 350 m gallery of the Horonobe Underground Research Laboratory (URL) with the Horonobe geological environment. In the Horonobe EBS experiment, various sensors were installed in the buffer and backfill material to obtain the data required to evaluate coupled THMC processes in near-field. In Task C of the Horonobe International Project (HIP), the dismantling experiment of the Horonobe EBS experiment will be carried out and the data obtained from this experiment will be used to understand the coupled processes and to evaluate the simulation code.
Hayano, Akira
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.134 - 139, 2024/12
In the design and construction of a repository for high-level radioactive waste, it is considered to set criteria for the rational locating of disposal tunnels and holes, taking into account the effects of faults and fractures distributed in the host rock at the tunnel to pit scale and excavation damaged zones (EDZs) that occur after tunnel excavation on the workability of the disposal tunnels and the long-term stability of the engineered barriers. In addition, tunnel sealing technologies such as tunnel backfilling and hydraulic plugs will be considered to prevent short-circuit flow of radionuclides through the excavated tunnels and the surrounding EDZs. In Task B of the HIP, we will attempt to establish criteria for the layout of disposal tunnels and holes, and the systematic integration of technical options related to the design, construction, operation and closure of the repository, using the investigation and construction at the Horonobe URL for Neogene sedimentary rocks as a case study. Based on information provided by the participating organisations and existing case studies from Japan and overseas, the current focus is on the reduction of the mechanical strength of the rock mass, the effects of water inflow on disposal tunnels and holes, or the effects on engineered barriers, in relation to the locating of disposal tunnels and boreholes and the emplacement of engineered barriers, and is currently working on analyses to predict features associated with these. Investigation, construction and testing of the 500 m niches No. 8 and No. 9 to confirm the validity of these predictions, and full-scale tunnel backfilling and hydraulic plug installation test in the 350 m Niche No. 6, will be carried out in Phase 2 of the HIP.
Miyakawa, Kazuya; Ishii, Eiichi; Imai, Hisashi*; Hirai, Satoru*; Ono, Hirokazu; Nakata, Kotaro*; Hasegawa, Takuma*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.82 - 95, 2024/12
no abstracts in English
Aoyagi, Kazuhei; Tachi, Yukio
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.124 - 127, 2024/12
Japan Atomic Energy Agency launched "Horonobe International Project (HIP)" utilizing the Horonobe Underground Research Laboratory. Currently, 11 organizations from 8 countries/regions are joining this project. The main objective of this project is to develop and demonstrate advanced technologies to be used in repository design, operation and closure and a realistic safety assessment in deep geological disposal, and to encourage and train the next generation of engineers and researchers. The research tasks consist of 1) Solute transport experiment with model testing, 2) Systematic integration of repository technology options, and 3) Full-scale EBS dismantling experiment. In these tasks, experimental galleries will be excavated and in situ experiments will be performed at these galleries, then the analysis and investigation methods will be validated. This is a unique and original aspect of the HIP and three research tasks described above are challenging from an international perspective. Thus, HIP can be a good practice of international collaboration utilizing the underground facility.
Mitsuguchi, Takehiro; Okabe, Nobuaki*; Kokubu, Yoko; Matsuzaki, Hiroyuki*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.96 - 110, 2024/12
Geological disposal of high-level radioactive waste requires not only selecting sites appropriate for the waste repository, where its isolation ability would not be damaged by natural phenomena for several tens of thousands of years, but also rationally constructing the disposal system depending on site-specific geological environments and their anticipated long-term variability. Recently, elemental/isotopic compositions of underground fluids (deep groundwaters, hot/cold spring waters, brines associated with oil and natural gas reservoirs, and so on) in Japan have been studied for evaluating the long-term stability of the geological environments of this country. Iodine and its radioactive isotope 
I (half-life = 15.7 million years) are included in the subjects of the study. The current review paper provides overviews of (i) the iodine content and iodine-129/127 ratio (I/
I ratio) of various materials in Earth's surface layers, (ii) relevant sample pretreatments and measurements, and (iii) I/I data of the underground fluids in Japan, then gives (iv) some interpretations of the fluid I/I data, along with their problems and uncertainties, and (v) some implications towards evaluating the long-term stability of geological environments.
Ozaki, Yusuke
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.128 - 133, 2024/12
Task A of the Horonobe International Project (HIP) aims to investigate the characteristics of solute transport of the Koetoi Formation at 250 m stage of the Horonobe underground research laboratory (URL). The objective of this task is to develop a modeling approach of solute transport considering actual phenomena occurring in the rock based on in-situ tracer experiments along with the discussion on transferability of data and modeling approach from different geological environment. Phase 1 of task A is divided into four subtasks of planning of in situ experiments, laboratory experiments, field experiments, and modeling. These subtasks are tackled by participating organizations as collaborative research, and I present the current situation of each subtask and our cooperation.
Kikuchi, Hirohito*; Uda, Toshiaki*; Hayashi, Daisuke*; Emori, Minoru*; Kimura, Shun
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(1), p.11 - 20, 2024/06
no abstracts in English
Takeda, Masaki; Ishii, Eiichi
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(1), p.3 - 10, 2024/06
Uunderstanding nuclide transport characteristics in the EDZ of disposal and access tunnels is an essential issue in the safety assessment of geological disposal of high-level radioactive waste. Although tracer tests are effective in evaluating the transport of nuclides in rock masses, the transport properties of EDZ in sedimentary rock, to our best knowledge, have not been investigated by in situ tracer tests. The authors conducted cross-hole tracer tests on EDZ fractures at the Horonobe Underground Research Laboratory to evaluate their longitudinal dispersibility. One-dimensional advection-dispersion analyses based on the tracer test data were performed, and the longitudinal dispersibility was estimated to be 0.12 m for the test scale of 4.2 m. This longitudinal dispersibility is 1/100 to 1/10 of the test scale, comparable with the empirical relationship between the test scale and longitudinal dispersibility for natural fractures and rock matrices. The series of tracer tests and analyses reported in this paper demonstrate that advection-dispersion occurs also in EDZ fractures similarly to natural fractures and rock matrices, and that longitudinal dispersibility in EDZ fractures can be assessed also by conventional in situ tracer test methods.
Takiya, Hiroaki
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 30(2), p.66 - 71, 2023/12
A half of unclear facilities in Japan Atomic Energy Agency (JAEA) has been transferred to decommissioning phase because of achieving the expected goals for the research and development, aging of buildings and equipment, etc. JAEA must safely, efficiently, and rationally implement back-end measures related to decommissioning, from the dismantling of nuclear facilities to the processing and disposal of radioactive waste generated by dismantling. The decommissioning and radioactive waste management head office collaborates with each JAEA's site to plan and promote comprehensive back-end measures and promote near surface disposal of low-level radioactive waste generated from research, medical, and industrial facilities, and to work on research and development aimed at solving common issues related to back-end measures, human resource development, etc. Since decommissioning is a long-term project, it is important to secure specialized human resources for the future. This article presents a summary of human resource development for decommissioning.
Sakamoto, Yoshiaki
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 30(1), p.15 - 18, 2023/06
The entire process of nuclear power generation is called the nuclear fuel cycle, and each process generates various types of radioactive waste. These radioactive wastes are generated from the operation and decommissioning of these facilities, and are treated and disposed of appropriately according to their radioactivity concentrations and properties. This paper describes the basic outline of the nuclear fuel cycle and the fundamentals of the treatment and disposal of radioactive waste (including radioactive waste from the use of radioactive materials in facilities other than the nuclear fuel cycle), called the back end of the nuclear fuel cycle.
Yotsuji, Kenji*; Tachi, Yukio; Sakuma, Hiroshi*; Kawamura, Katsuyuki*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.63 - 81, 2022/12
The understanding of the swelling phenomenon of montmorillonite is essential to predict the physical and chemical behavior of clay-based barriers in radioactive waste disposal systems. This study investigated the key factors controlling crystalline swelling behavior of montmorillonite with different interlayer counter-ions by molecular dynamics (MD) simulations. On the basis of the comparisons between MD simulated and experimental results, the water content in the interlayer in five homoionic (Na
, K, Cs, Ca and Sr) montmorillonite was strongly correlated to the hydration number and the preference of an outer- or inner-sphere complex of each counter-ion. The detailed analysis for these results offer insights that the hydration number is controlled by the hydration free energy, the volume and the distribution of each interlayer counter-ion. The systematic MD simulations with virtually variable parameters clarified that the hydration free energy and the charge of interlayer counter- ions compete as influencing factors, and the control the formation rate of an outer-sphere complex of each counter-ion. The empirical relationships between these key factors will allow essential insights into predicting the swelling behavior of montmorillonite with different interlayer counter-ions.
Sasao, Eiji
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.142 - 147, 2022/12
Japan Atomic Energy Agency (JAEA) has been engaged in research and development (R&D) on deep geological disposal of high-level radioactive waste over the years. In this paper, the current status of R&D activities is presented. JAEA is the only research organization in Japan that has underground research facilities, and this paper focuses on the underground research laboratory projects at the facility. R&D on deep geological disposal was initiated in 1976 in Japan and has been performed by JAEA and other R&D organizations. This paper also briefly summarizes the history of R&D and introduces the basic concept of geological disposal in Japan.
Takayama, Yusuke; Sato, Daisuke*; Kikuchi, Hirohito*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.101 - 111, 2022/12
Swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. It has been reported that the swelling pressure obtained by swelling pressure test increases monotonically or temporarily decreases after increasing with the passage of the time depending on the initial water content. In this study, swelling pressure tests were conducted under several different initial water content conditions, and the change in wet density distribution inside the specimen during the swelling pressure tests was observed by X-ray CT measurement. It was confirmed that the presence or absence of collapse behavior and its magnitude affect the shape of the change in swelling pressure. When the collapse deformation was large, the amount of temporary decrease in swelling pressure was large. On the other hand, swelling pressure increased monotonically when there was no deformation due to collapse.
Sasao, Eiji
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.112 - 118, 2022/12
Since fractures in granite act as pathways for groundwater flow and mass transport, understanding of fracture distribution is an important subject for the disposal of high-level nuclear waste. Fracture data obtained through the borehole investigation from ground surface contains errors due to the crossing angle between boreholes and fractures. I studied method of borehole investigation that can effectively characterize the fracture distribution based on fracture information obtained from geological investigation of shaft wall at the Mizunami Underground Research Laboratory. As a result, it was found that inclined boreholes captured larger number of fractures than vertical boreholes. Therefore, inclined boreholes are preferable for efficient characterization of the fractures. Fracture orientation at surface exposure is well concordant with that at the shaft, which implies that the drilling direction should be determined based on the result of surface fracture mapping.
Yamaguchi, Masaaki
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(1), p.38 - 41, 2022/06
This presentation outlined the framework and background of Japan's geological disposal research that has been underway since the 1970s and outlined research and development on the engineering technology of geological disposal and the performance assessment of geological disposal systems in the research and development fields. Specific assessment methods used in both R&D fields and recent research topics were also explained.
Seki, Misaki; Fujita, Yoshitaka; Fujihara, Yasuyuki*; Zhang, J.*; Yoshinaga, Hisao*; Sano, Tadafumi*; Hori, Junichi*; Nagata, Hiroshi; Otsuka, Kaoru; Omori, Takazumi; et al.
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(1), p.2 - 9, 2022/06
no abstracts in English
Sakai, Akihiro
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(1), p.48 - 54, 2022/06
no abstracts in English
Osawa, Hideaki; Matsui, Hideki
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 28(2), p.18 - 25, 2021/12
The Japan Atomic Energy Agency had offered visitor's tour to the underground and surface facilities of the Mizunami Underground Research Laboratory (URL) at the Tono Geoscience Center in order to promote the understanding of the R&D of geological disposal technology and geological disposal for the public. We analyzed questionnaires distributed after visiting these facilities from FY2010 to FY2019, except for FY2016, in the hopes of using risk communication for geological disposal. Results suggest that visiting these facilities is a valuable experience to understand geological disposal because some people, knew even just a little bit about it, have positively evaluated appropriateness of geological disposal by a tour of the Mizunami URL. While some people who have negatively evaluated safety of geological disposal are highly interested in issues of nuclear power and site selection, some people who have positively evaluated safety of geological disposal are highly interested in public understanding of geological disposal. Furthermore, both these groups believe that long-term safety is a technical issue.
Sugiura, Yuki
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 28(1), p.5 - 7, 2021/06
no abstracts in English
Kitamura, Akira; Akahori, Kuniaki; Nagata, Masanobu*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(2), p.83 - 93, 2020/12
Direct disposal of spent nuclear fuel (SNF) in deep underground repositories (hereafter "direct disposal") is a concept that disposal canisters stored fuel assemblies dispose without reprocessing. Behavior of radionuclide release from SNF must be different from that from vitrified glass. The present study established a methodology on determination of instant release fraction (IRF) of radionuclides from SNF, which is the one of the parameters on radionuclide release based on the latest safety assessment reports in other countries, especially for IRF values proportional to a fission gas release ratio (FGR). Recommended and maximum values of FGR have been estimated using the fuel performance code FEMAXI-7 after collecting FGR values on Japanese SNFs. Furthermore, recommended and maximum values of IRF for Japanese SNFs used in a pressurized water reactor (PWR) have been estimated using the presently obtained FGR values and experimentally obtained IRF values on foreign SNFs. The recommended and maximum IRF values obtained in the present study have been compared with those of the latest safety assessment reports in other countries.
