Imai, Hisashi*; Amemiya, Kiyoshi*; Matsui, Hiroya; Sato, Toshinori; Saegusa, Hiromitsu; Watanabe, Kunio*
Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 69(3), p.285 - 296, 2013/07
The more accurate understanding and appropriate control of unsaturated area around tunnel excavated in deep rock-mass are required, for the geological isolation of radioactive waste project and also underground rock cavern storage project of liquefied petroleum gas. The numerical simulation of seepage flow is usually conducted to understand and evaluate the unsaturated zone around tunnel. The unsaturated parameters (such as moisture characteristic curve and relative permeability) and appropriate control of boundary condition are indispensable for the simulation. Authors developed methodology to measure unsaturated parameters utilizing the measuring method conventionally applied to soils and showed the efficiency of the method via a laboratory experiment. The idea of combining seepage face condition and flow rate fixed condition was derived, and the efficiency was shown in an model simulation. The two developments enabled the accurate estimation and understanding the evolution of unsaturated zone around tunnel.
Suzuki, Hideaki; Nakama, Shigeo; Fujita, Tomo; Imai, Hisashi; Sazarashi, Masami
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 19(2), p.39 - 50, 2012/12
For the safety assessment of a geological disposal system for high-level radioactive waste, it is necessary to quantify coupled thermo-hydro-mechanical-chemical (THMC) processes in the near-field. The current study investigated the geochemical changes arising from the infiltration of groundwater into the bentonite buffer under a thermal regime of radiogenic heating arising from the vitrified waste with the computer simulated assistance of a developed THMC model. In the case of infiltration by a saline groundwater, sulfate precipitates as gypsum around the overpack in the bentonite buffer and the Na-type bentonite changes to Ca-type by exposure to Ca ions released from concrete supports. In addition, the temporal evolution of the bentonite buffer porewater composition can be obtained to assess its contribution to the corrosion of the overpack.
Niizato, Tadafumi; Imai, Hisashi*; Maekawa, Keisuke; Yasue, Kenichi; Kurikami, Hiroshi; Shiozaki, Isao*; Yamashita, Ryo*
Proceedings of 19th International Conference on Nuclear Engineering (ICONE-19) (CD-ROM), 10 Pages, 2011/10
A critical issue for building confidence in the long-term safety of geological disposal is to demonstrate the stability of the geosphere, taking into account its likely future evolution. This study aims to establish comprehensive techniques for characterising the overall evolution of coastal sites through studying the palaeohydrogeological evolution in the coastal system around the Horonobe area, Hokkaido, northern Japan. Information on natural events and processes related to the palaeohydrogelogical evolution of the area have been integrated into the conceptual models that indicates the temporal and spatial sequences of the events and processes, such as climatic and sea-level changes, palaeogeography, and geomorphological and geological evolution in the area. The groundwater flow simulation, which is based on the conceputualisation of the long-term geosphere evolution, shows the sensitivities of natural events and processes on groundwater flow properties in a coastal setting.
Imai, Hisashi*; Yamashita, Ryo*; Shiozaki, Isao*; Urano, Kazuhiko*; Kasa, Hiroyoshi*; Maruyama, Yoshio*; Niizato, Tadafumi; Maekawa, Keisuke
JAEA-Research 2009-001, 116 Pages, 2009/03
Evaluation of long-term geological evolution and its impact on groundwater flow is one of the major themes within the frame of Horonobe Underground Research Laboratory Project. For the purpose of development of a groundwater flow modeling methodology considering the effects of long-term geological evolution, following three items were studied: (1) Upgrade of SMS (Sequential Modeling System of geo-environmental evolution impact on groundwater flow) which was developed in 2006 FY; (2) Groundwater flow simulation under more realistic conditions of geological structures and hydrogeological conditions; and (3) Sensitivity study of geo-environmental evolution impacts on groundwater flow. The studies showed following suggestive results. (1) Development of a precise time step setting enabled to narrow the gaps in simulated head between time steps in which the model configuration used to deformed. (2) Several aspects have been found from studies on impact factors such as deposition on pore pressure, recharge rate and difference in density of saline groundwater. For evaluation of pore pressure induced by deposition, it is necessary to model the porosity and permeability variation considering the exceed pore pressure change. The setting of recharge rate during the Ice Age influence the characteristics of groundwater flow in coastal and hilly areas. The density of groundwater is not so influential as topological potential factors, however it is effective for the characteristics of groundwater flow in coastal area and intrusion of recharge water from ground surface. (3) The sensitivity study on faulting characteristics indicated that the two types of fault configuration and the hydraulic conductivity setting considered are not influential on the nature of groundwater flow above the depth of 500 m.
Kurikami, Hiroshi; Yasue, Kenichi; Niizato, Tadafumi; Imai, Hisashi*; Shiozaki, Isao*; Yamashita, Ryo*
Chikasui Ryudo Kaiseki To Moderuka Ni Kansuru Shimpojium Happyo Rombunshu, p.59 - 66, 2007/01
no abstracts in English
Chijimatsu, Masakazu*; Fukudome, Kazuto*; Urano, Kazuhiko*; Imai, Hisashi*; Sasaki, Hajime*; Amemiya, Kiyoshi*
JNC TJ8400 2004-027, 87 Pages, 2005/02
This study investigates the methodology for the engineered barriers performance confirmation. First of all the investigation about the monitoring concept in foreign countries were performed and the monitoring aiming was fixed at the performance confirmation of the engineered barriers. The monitoring item and the element of engineered barriers were set as followings, namely temperature, hydraulic pressure, water contents, pH, Eh and the chemistry of solutions. The indirect measuring method of items both providing the engineered barriers performance and varying with exhibition of performance from the rock around the engineered barriers is proposed for the engineered barriers performance confirmation monitoring.
Imai, Hisashi*; Shiozaki, Isao*
JNC TJ5440 2004-001, 80 Pages, 2004/11
To understand the deep underground geological environment around the Horonobe Underground Research Laboratory, and to estimate the underground facility construction effect on the geological environment, renewal of the existing hydrogeological model and groundwater flow simulations were carried out.
Chijimatsu, Masakazu*; Imai, Hisashi*; Sasaki, Hajime*; Moro, Yoshiji*
JNC TJ8400 2003-090, 116 Pages, 2004/02
This study investigates the methodology for the engineered barriers performance confirmation. First of all the investigation about the monitoring concept in foreign countries were performed and the monitoring aiming was fixed at the performance confirmation of the engineered barriers. The monitoring item and the element of engineered barriers were set as followings, namely temperature, hydraulic pressure, water contents, pH, Eh and the chemistry of solutions. The indirect measuring method of items both providing the engineered barriers performance and varying with exhibition of performance from the rock around the engineered barriers is proposed for the engineered barriers performance confirmation monitoring. Finally the problems to be solved for the future monitoring program are clarified, and the plan of R&D for sensing methods in the performance assessment, and the in-situ experimental plan in the Horonobe deep underground research center are proposed.
Chijimatsu, Masakazu*; Imai, Hisashi*; Fukudome, Kazuto*; Kayukawa, Koji*; Sasaki, Hajime*; Moro, Yoshiji*
JNC TJ8400 2003-089, 354 Pages, 2004/02
After emplacement of the engineered barrier system (EBS), it is expected that the near-field environment will be impacted by phenomena such as heat dissipation by conduction and other heat transfer mechanisms, infiltration of groundwater from the surrounding rock in to the engineered barrier system, stress imposed by the overburden pressure and generation of swelling pressure in the buffer due to water infiltration. In order to recognize and evaluate these coupled thermo-hydro-mechanical (THM) phenomena, it is necessary to make a confidence of the mathematical models and computer codes. Evaluating these coupled THM phenomena is important in order to clarify the initial transient behavior of the EBS within the near field. DECOVALEX project is an international co-operative project for the DEvelopment of COupled models and their VALidation against EXperiments in nuclear waste isolation and it is significance to participate this project and to apply the code for the validation. Therefore, we tried to apply the developed numerical code against the subjects of DECOVALEX. We carried out the simulation against the Task1 (simulation of FEBEX in-situ full-scale experiment), Task 3 BMT1 (Bench Mark Test against the near field coupling phenomena) and Task3 BMT2 (Bench Mark Test against the up-scaling of fractured rock mass). This report shows the simulation results against these tasks. Furthermore, technical investigations about the in-situ full-scale experiment (called Prototype Repository Project) in Aspo HRL facility by SKB of Sweden were performed. In order to evaluate the coupled phenomena in the engineered barrier, we use the new swelling model based on the theoretical approach. In this paper, we introduce the modeling approach and applicability about the new model.
Imai, Hisashi*; Fukudome, Kazuto*; Kayukawa, Koji*; Sasaki, Hajime*; Chijimatsu, Masakazu*; Moro, Yoshiji*
JNC TJ5400 2003-009, 223 Pages, 2004/02
In order to search for an appropriate methodology of the regional groundwater flowanalysis for sedimentary rock mass area, the following four studies were carried out: 1) Two simulation region setting and data set arrangement of the two region for numerical simulation of groundwater flow 2) Evaluation of regional groundwater flow characteristics in the Horonobe Project site using the results of the numerical simulation and obtained field data 3) Estimation of the shaft excavation effect on the groundwater flow such as the inflow rate of groundwater into the shafts, the chroline contents of groundwater flowing into the shafts and the hydraulic head evolution around the shafts 4) Proposal of desirable investigations for the next stage : the methodology of evaluating groundwater flow characteristics
Imai, Hisashi*; *; Yamashita, Ryo*; *; Amemiya, Kiyoshi*; Chijimatsu, Masakazu*
JNC TJ1400 2002-004, 357 Pages, 2002/03
Imai, Hisashi*; Yamashita, Ryo*; Amemiya, Kiyoshi*; Shiozaki, Isao*
JNC TJ1410 2001-002, 318 Pages, 2001/08
Yamashita, Ryo*; Imai, Hisashi*; *; *; Amemiya, Kiyoshi*; *
JNC TJ1420 2000-008, 176 Pages, 2000/03
Imai, Hisashi*; Amemiya, Kiyoshi*
JNC TJ7412 98-005, 35 Pages, 1998/03
Imai, Hisashi*; Nishida, Kaoru*; *; Amemiya, Kiyoshi*; Lin, Weiren*
PNC TJ1449 98-004, 231 Pages, 1998/02
Imai, Hisashi*; Amemiya, Kiyoshi*; Nishida, Kaoru*; Lin, Weiren*; *
PNC TJ1449 97-002, 261 Pages, 1997/03
no abstracts in English
Imai, Hisashi*; Amemiya, Kiyoshi*; Nishida, Kaoru*; Lin, Weiren*; *; Senna, Shigeki*
PNC TJ1449 96-005, 76 Pages, 1996/03
Amemiya, Kiyoshi*; Imai, Hisashi*; Chijimatsu, Masakazu*; Nishida, Kaoru*; Lin, Weiren*; Senna, Shigeki*
PNC TJ1449 95-006, 69 Pages, 1995/03
no abstracts in English
; ; Koide, Kaoru; Imai, Hisashi*; Yanagizawa, Koichi
PNC TN7410 94-029, 60 Pages, 1994/05
An extensive study program has been carried out by PNC to estimate hydrogeological characteristics of deep underground in Japan. As a part of this program, groundwater flow analyses in Northeast Japan were conducted. For the analyses of Northeast Japan area (300 500km 10 km deep), a hydrogeological model expressing topography, distribution of hydraulic conductivity was developed with information available from open literature. By the use of this model, steady state three-dimensional groundwater flow under a saturated-unsaturated condition was calculated by means of finite element method. The results are as follows : (1)Distribution of piezometric head corresponds with topography in the study area. (2)Piezometric head distribution is hydrostatic below E,L. -1000 m in thc study area. (3)Hydraulic gradient in the study area is less than 0.04 below E.L. -500 m. (4)Analytical seepage points appear in principal catchment areas. (5)Difference of boundary conditions such as permeable or impermeable at the shore side of this model does not affect the results of the analyses. (6)In case of setting higher hydraulic conductivity to Holocene and Pleistocene scdimentary rocks than that to Pliocene sedimentary rocks, the results of the analysis are as same as the inverse case while discharge rate decreases.