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Osawa, Hideaki
Gijutsushi "Chubu", (15), p.40 - 47, 2025/03
This paper introduces the history of the development of borehole investigation techniques at the Tono Geoscience Center of the Japan Atomic Energy Agency (JAEA), which started in 1986, as one of the research of geological environmental characteristics.
Aoyagi, Kazuhei; Ozaki, Yusuke; Ono, Hirokazu; Ishii, Eiichi
Dai-16-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), p.269 - 274, 2025/01
We investigated the development of the excavation damaged zone (EDZ) induced by the excavation of modeled disposal pit which was excavated as a part of the full-scale engineering barrier experiment at 350 m depth. Seismic and electric tomography surveys, observation of rock core samples, borehole televiewer surveys and three-dimensional excavation analysis were performed to evaluate the extent of the EDZ around the pit. It was clarified that the EDZ was developed 0.8 to 1.6 m from the wall of the pit at a relatively shallower depth caused by the effect of the EDZ induced around the floor of the gallery. The extent of the EDZ was gradually reduced along the depth, and the maximum extension was 0.3 m from the wall of the pit at the deeper section.
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.
Niunoya, Sumio*; Hata, Koji*; Aoyagi, Kazuhei; Matsui, Hiroya
Tonneru Kogaku Hokokushu (CD-ROM), 34, p.IV-1_1 - IV-1_6, 2024/12
A multi-optical measurement probe consisting of an optical fiber AE sensor, a pore pressure sensor, and a thermometer was installed at a depth from 350 to 370 m of the East access shaft. Using this measurement system, we continuously monitored the EDZ around the shaft and changes in pore water pressure. In this report, we summarized the measured AE and pore pressure data during the maintenance period after the completion of excavation to a depth of 350 m, and analyze the waveform data when earthquake occurred. We also investigated whether the measurement system can capture the effect of seismic motion to the EDZ. As a result, the AE count was slightly increased and pore pressure was slightly changed owing to the seismic motion, however, there is little impact to the EDZ.
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.
Aoyagi, Kazuhei; Sugawara, Kentaro*; Kamemura, Katsumi*; Nago, Makito*
International Journal of Rock Mechanics and Mining Sciences, 178, p.105776_1 - 105776_11, 2024/06
Times Cited Count：0 Percentile：0.00(Engineering, Geological)A method for estimating the stress state during the construction of underground facilities such as deep geological disposal repositories is necessary to enhance the reliability of their design, construction, and long-term performance. For this purpose, numerous in situ measurements of variables such as hydraulic fracturing or the stress relief method have been typically performed to estimate the stress state. However, it is difficult in some cases to validate the stress state, particularly in sedimentary rock, because of the variation related to heterogeneous rock masses and topography. This study developed a new method for reliably estimating the in situ stress state of rocks using the measured initial elastic displacement of the loop gallery at 350 m depth in the Horonobe Underground Research Laboratory (URL), Japan. The estimated magnitudes of the maximum and minimum horizontal stresses are 11.25 and 6.25 MPa, respectively, which are similar to the stresses measured using the hydraulic fracturing method performed before excavating the facility. Although the proposed method could only be applied after excavation of the gallery in the studied case, it yielded an estimate of the stress state over a region of hundreds of square meters with high accuracy, as assessed by comparison with measured results. We conclude that the method can be applied to optimizing the design, construction, and performance of large underground facilities, such as deep geological repositories.
Mitsui, Seiichiro
NUMO-TR-24-02, p.29 - 31, 2024/06
The Power Reactor and Nuclear Fuel Development Corporation (reorganized into the Nuclear Fuel Cycle Development Agency in 1998, merged with the Japan Atomic Energy Research Institute, and since 2005 has become the Japan Atomic Energy Agency) has been conducting natural analogue studies on the geological disposal system of radioactive waste since JFY1986. Here, we will provide an overview of the natural analogue studies on the long-term behavior of engineered barriers.
Takahashi, Rieko*; Taniguchi, Naoki
Zairyo To Kankyo, 73(6), p.153 - 163, 2024/06
Carbon steel is one of the candidate materials for overpacks in geological disposal of high-level radioactive waste, and is known to susceptible to stress corrosion cracking(SCC) depending on the condition in carbonate environment. In order to understand the influence of temperature on the SCC susceptibility of carbon steel, slow strain rate test (SSRT) of rolled steel were performed in NaHCO
aqueous solution with varying temperature in the range of 303-393K for conditions of 0.1-0.5 mol/dm
, which is assumed to be the upper limit of carbonate concentration in groundwater in a geological disposal environment. As the results, no obvious influence of temperature on mechanical properties such as fracture strain ratio and reduction area ratio were observed, but SCC susceptibility based on SCC fracture ratio increased at relatively low temperatures of 303K and 323K. It was suggested that the reason for the higher SCC sensitivity at lower temperatures was due to slower repassivation at lower temperatures. Regarding the type of SCC, intergranular SCC was dominant at low temperatures and tended to transition to intergranular SCC at higher temperatures. Transgranular SCC tended to be observed at lower potentials than those at which intergranular SCC was observed.
Yamaguchi, Masaaki; Suzuki, Yuji*; Kabasawa, Satsuki; Kato, Tomoko
JAEA-Data/Code 2024-001, 21 Pages, 2024/03
JAEA-Data-Code-2024-001.pdf:3.45MB
JAEA-Data-Code-2024-001-appendix(CD-ROM).zip:8.0MB
Model catchments have developed for use in testing various assessment models that can consider specific surface environmental conditions such as topography, riverine systems, and land use in the biosphere assessment of HLW geological disposal. The model catchments consist of the topography and riverine system of the catchment area created using existing tools, as well as land use and population distribution, river discharge, sediment flux data set by algorithms from topographical data. Datasets of three types of model watersheds (Types 1 to 3, watershed area: 730 to 770 km
) with different topographical characteristics have released as raster data that can be handled by geographic information systems (GIS). Since the model catchments were created virtually reflecting as much as possible the main characteristics of Japan's surface environment, they can be used as a test bed for conducting hydraulic/mass transport analysis to set the GBI and compartment model.
Kumagai, Yuta
Hoshasen (Internet), 49(1), p.15 - 17, 2024/03
Water radiolysis induces oxidative dissolution of uranium oxides. Understanding of this process is a chemical basis for safety assessment of the deep geological repository of spent fuel and would serve as knowledge for retrieval and storage of fuel debris after a severe accident of nuclear power reactors. In order to evaluate the release rate of radioactive elements from the UO
matrix of spent nuclear fuel, several chemical kinetic models have been developed. However, the conventional reaction models were found out to be simplistic based on new insights obtained recent experimental studies. Therefore, the reaction mechanism of surface oxidation and dissolution of uranium is now a subject of revisit. Here, a few recent studies regarding the reaction mechanism are introduced.
Aoyagi, Kazuhei; Ishii, Eiichi
Environmental Earth Sciences, 83(3), p.98_1 - 98_15, 2024/02
Times Cited Count：2 Percentile：60.01(Environmental Sciences)The long-term geological disposal of high-level radioactive waste relies on predictions of future changes in a disposal facility's hydro-mechanical characteristics to assess potential leakage through fractures in the excavation damaged zone (EDZ) after backfilling the facility. This study evaluated the transmissivity of EDZ fractures using in situ hydraulic tests around the area of a full-scale, experimental, engineered barrier system in the Horonobe Underground Research Laboratory, Hokkaido, Japan. After their installation, the buffer blocks swelled, altering the stresses within the EDZ fractures. The effects of these changing stresses on the fractures' transmissivity were assessed over a period of 4 years. The transmissivity continuously decreased in this period to about 41% of its value measured prior to the swelling. Using the Barton-Bandis normal-stress-dependent fracture-closure model, the decrease in transmissivity is quantitatively attributed to closure of the EDZ fractures, which was caused by the swelling pressure increasing up to 0.88 MPa. Evidence of fracture closure came from seismic tomography surveying, which revealed a slight increase in seismic velocity in the study area with increasing swelling pressure. The results show that EDZ fractures were closed by swelling of the full-scale buffer material. They also demonstrate the applicability of the Barton-Bandis model to preliminary estimation of the long-term transmissivity of EDZ fractures in facilities for the geological disposal of radioactive waste.
Matsueda, Makoto
Chino To Joho, 35(4), P. 88, 2023/11
Radioactive waste is what contains radioactive materials generated through nuclear activities, radiopharmacy, research and development. The treatment and disposal of the waste are one of the key challenges facing people. This glossary describes the classification of radioactive waste, the challenges and the current efforts of its disposal and current efforts, and so on.
Tachi, Yukio
Kagaku To Kyoiku, 71(10), p.420 - 423, 2023/10
no abstracts in English
Sato, Hisashi*; Takayama, Yusuke; Suzuki, Hideaki*; Sato, Daisuke*
JAEA-Data/Code 2023-010, 47 Pages, 2023/09
JAEA-Data-Code-2023-010.pdf:1.45MB
When a high-level radioactive waste repository is constructed in a coastal area, it is necessary to fully evaluate the impact of seawater-based groundwater on engineered barriers, including buffer materials. In this report, one-dimensional saltwater infiltration tests were conducted to obtain data to understand the impact of seawater-based groundwater on the migration phenomena of water and solutes in the buffer material during the transient period. As a result, it was confirmed that the infiltration rate increased as the NaCl concentration in the infiltration solution increased. And it was confirmed that the water content ratio distribution changed as the NaCl concentration in the infiltration solution increased. As a result of analysis of the chloride ion concentration of the post-test specimens confirmed that chloride ion enrichment was occurred with infiltration. As a result of verifying the mechanism by which chloride ion enrichment occurs, it was confirmed that the phenomenon of chloride ion enrichment due to infiltration depends on the initial water content ratio.
Osawa, Hideaki
Gijutsushi "Chubu", (12), p.34 - 41, 2023/09
This introduces current status of Toki Geochronology Research Laboratory, Tono Geoscience Center, Japan Atomic Energy Agency.
Mitsui, Seiichiro
Kinzoku, 93(3), p.211 - 218, 2023/03
As part of research and development of geological disposal, "natural analogues" have been applied to validate concept of models and evaluation methodologies for performance assessment. By introducing our research results on natural analogues, this paper presents how we have utilized knowledge of excavated archaeological artifacts for geological disposal studies.
Yanagida, Akinobu*; Ura, Yoko*; Mitsui, Seiichiro; Ishidera, Takamitsu; Kawakita, Ryohei
Nara Bunkazai Kenkyujo Soritsu 70-Shunen Kinen Rombunshu; Bunkazai Ronso 5, p.843 - 856, 2023/03
To investigate chloride salt accumulation inside an iron artifact in soil, non-destructive analysis of three iron artifacts excavated from the Heijo Palace Site was conducted using elemental mapping by X-ray fluorescence analysis, micro-X-ray diffraction analysis, and X-ray computed tomography. Furthermore, the buried environments of the artifacts were presumed based on the previous reports of the environmental investigation at the Heijo Palace site. The results revealed the iron artifact's corrosion behavior was different individually- (1) the iron artifact that was presumed buried under oxidation environments had a goethite/magnetite corrosion layer and contained akageneite inside the corrosion layer. (2) the metal of the other iron artifacts buried under the oxidation environment had eluted absolutely and the artifacts had a rust layer formed by only goethite. (3) the other artifact buried in reduction environments had a rust layer composed of siderite. Accumulation of chloride salts inside an iron artifact was observed only in (1). Because each Cl
concentration measured in underground water observation holes at the Heijo Palace Site showed almost the same level concentrations, it was presumed that the accumulation of chloride salts depended on the environmental factor except for Cl concentration. Based on these results, there was a possibility that the occurrence of local corrosion attributed to the separation of anodic and cathodic regions through the formation of the goethite/magnetite rust layer caused chloride salts accumulation inside an iron artifact.
Geological Disposal Research and Development Department
JAEA-Evaluation 2022-007, 81 Pages, 2022/11
JAEA-Evaluation-2022-007.pdf:2.06MBJAEA-Evaluation-2022-007-appendix(CD-ROM).zip:37.06MB
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 post- and pre-review assessment 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 and the efficiency of the project implementation during the period of the current and next plan. This report summarizes the results of the assessment by the Committee with the Committee report attached.
Makino, Hitoshi; Semba, Takeshi; Shibata, Masahiro
NEA/RWM/R(2018)7 (Internet), p.315 - 322, 2022/11
This presentation summarize challenge on development of an advanced KMS by JAEA including the background to this initiative, the basic approach selected, a developed prototype of the JAEA KMS, and challenges and practical issues for introduction and also sustainable maintenance of the JAEA KMS.
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.
