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JAEA Reports

Waste acceptance criteria for waste waste package destined fot trench-type disposal facilities for waste generated from Research, Industrial and Medical Facilities; No harmful void

Nakata, Hisakazu; Takao, Hajime*; Chijimatsu, Masakazu*; Noma, Yasutaka*; Amazawa, Hiroya; Sakai, Akihiro

JAEA-Technology 2018-014, 43 Pages, 2019/03

JAEA-Technology-2018-014.pdf:5.91MB

Japan Atomic Energy Agency plans to install disposal facilities for radioactive waste arising from research institutes. One relevant technical standard by the safety regulation is that the disposal facility shall be performance so as not to be left with harmful voids after backfilling with soil. Additionally no harmful void needs to exist in the waste packed in metal containers. The harmful void is supposed to result in the collapse of the disposal facility after structural materials of the container deteriorate and then become a state that can not retain the structure on its own. That leads to have an adverse impact on the facility such that the shape of cover soil deforms the way in which stagnant water is likely to occure. For which reason, a waste acceptance criteria relating to the quantity of voidage in a waste package needs to be defined quantitatively, which is preliminary less than 20% in a volum ratio based on this study.

Journal Articles

Numerical simulations and analysis for the $"A$sp$"o$ pillar stability experiment, 1; Continuum based approaches using finite element method and comparison with other analysis model

Chijimatsu, Masakazu*; Koyama, Tomofumi*; Shimizu, Hiroyuki*; Nakama, Shigeo; Fujita, Tomoo

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.437 - 442, 2013/01

DECOVALEX-2011 is an international cooperation project for enhancing the numerical models of radioactive waste repositories. In Task B of DECOVALEX-2011 project, the failure mechanism during excavation, heating and destressing processes observed in the $"A$sp$"o$ pillar stability experiment (APSE), which carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB), were simulated using Finite Element Method. When the calibrated parameters were used, simulation results agree qualitatively well with the experimental results. Therefore, it can be said that the spalling phenomenon is expressible even by the application with the continuum model by the use of the suitable parameters.

Journal Articles

Numerical simulations and analysis for the $"A$SP$"O$ pillar stability experiment, 2; Discontinuum based approaches using distinct element method

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.443 - 448, 2013/01

DECOVALEX-2011 is an international cooperation project for enhancing the numerical models of radioactive waste repositories. In Task B of DECOVALEX-2011 project, the failure mechanism during excavation, heating and destressing processes observed in the $"A$sp$"o$ pillar stability experiment (APSE), which carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB), were simulated using two dimensional Distinct Element Method. As a result, it is found that the simulated crack generation and propagation during the destressing process by 2D-DEM agree qualitatively well with the observation at site.

Journal Articles

Distinct element analysis for mechanical behavior in HLW disposal tunnel considering pre-existing cracks

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Doboku Gakkai Rombunshu, A2 (Oyo Rikigaku) (Internet), 68(2), p.I_477 - I_486, 2012/00

In this paper, the coupled thermal-mechanical processes in the $"A$sp$"o$ pillar stability experiments (APSE) were simulated using Distinct Element Method (DEM). By considering pre-existing cracks in the rock model, mechanical response of the rock during excavation phase and heating phase were successfully represented by DEM. Simulation results agree qualitatively well with the experimental results. However, the microcracks in the simulation were widely distributed around the heater and exfoliation of rock surfaces observed in the ${it in-situ}$ experiment was not formed accurately. To simulate more realistically the experimental results by the DEM models, the calibration of the microscopic parameters considering the model scale should be done. Moreover, more detailed discussion on the excavation damaged zone around the borehole and the distribution of pre-existing cracks are required.

Journal Articles

Distinct element modeling for Class II behavior of rock and hydraulic fracturing

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Murata, Sumihiko*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

International Journal of the JCRM (Internet), 7(1), p.33 - 36, 2011/09

In this research, newly developed numerical approaches using the Distinct Element Method (DEM) were presented, and a series of DEM simulations were performed for better understanding the physical phenomena and mechanism for the following two fundamental issues in rock engineering field. The first issue is the Class II behavior of the brittle rocks under uniaxial compression. The radial strain control method for uniaxial compression tests was introduced in the DEM codes and the Class II behavior of rocks was simulated. The simulation results suggest that the DEM can reproduce the Class II behavior of the rock successfully and revealed that the loading condition of rocks will play an important role for the Class II behavior. The second issue is the hydraulic fracturing behavior in rocks. A series of simulations for hydraulic fracturing in rock was performed by using the flow-coupled DEM code. Simulation results clearly show that the fluid infiltration behavior depends on the fluid viscosity. The fluid infiltrates into the fracture immediately, when a low viscosity fluid is used and the fluid infiltrates slowly into the cracks after the fracture generation and propagation, when a high viscosity fluid is used. Moreover, the tensile cracks are dominantly generated in the DEM simulations as expected in the conventional theory. However, the energy released from tensile cracks becomes smaller due to the fact that the tensile strength of rock is usually smaller than the compressive one. Such a small AE events is not distinguishable from noise and hard to recognize during laboratory experiments. Therefore, in AE measurements, shear type AE events with large energy are dominantly observed.

Journal Articles

Simulation of the spalling phenomena at the $"A$sp$"o$ Pillar Stability Experiment by the coupled T-H-M analysis using the damage model

Chijimatsu, Masakazu*; Koyama, Tomofumi*; Kobayashi, Akira*; Shimizu, Hiroyuki*; Nakama, Shigeo

Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 13 Pages, 2011/07

The experiment was performed at the $"A$sp$"o$ Hard Rock Laboratory facility owned by the Swedish Nuclear Fuel and Waste Management Co. For the experiment an oval shape tunnel was excavated in which two large holes, $$phi$$ 1.75 m and depth 6.5 m, were excavated. The holes were placed so that a 1 m wide vertical pillar was created between them. The pillar volume was then heated to increase the tangential stress so that yielding could propagate along the borehole wall. Analysis of the coupled thermal, hydraulic and mechanical processes is carried out with the computer code named THAMES. In order to evaluate the spalling phenomena, the damage model was included in the computer code. In the damage mechanics, the change in mechanical behavior due to the growth of damage (cracks) in material is considered. The parameters of this damage model were determined by the unconfined compression test. When the parameters determined by laboratory test were used, the damage did not occur. This is because the parameters were determined from the experiment of the rock core, and it is thought that the parameter of actual bedrock is inferior to that of the rock core. Therefore, the calibration of the damage parameters was performed. When the calibrated parameters were used, simulation results agree qualitatively well with the experimental results. During the simulation of excavation, generating of damage is seen to similar to the observation by the in-situ experiment. Furthermore, temperature change during heating after the excavation of borehole also shows the good agreement between the measured and simulated results. Therefore, it can be said that the spalling phenomenon is expressible even by the application with the continuum model by the use of the suitable parameters.

Journal Articles

Numerical simulations for the coupled thermal-mechanical processes in $"A$sp$"o$ Pillar Stability Experiment; Continuum and discontinuum based approaches

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Kobayashi, Akira*; Nakama, Shigeo; Fujita, Tomoo

Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 11 Pages, 2011/07

In this paper, the coupled thermal-mechanical processes in the pillar stability experiments carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both Finite Element Method (FEM) and Distinct Element Method (DEM) with particles. The main purpose for in-situ experiment is to investigate the yielding strength of crystalline rock and the formation and growth of the excavation disturbed/damaged zone (EDZ) during excavation and heating processes. For the 3-D numerical simulations using FEM (called THAMES), the measured in-situ stress and its time evolutions (stress re-distribution) due to the tunnel and two borehole excavations, pressurize in one of the borehole as well as heating process were considered. On the other hand, in 2-D DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface (spalling phenomena). The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculation results such as stress distribution, displacements as well as temperature distribution were compared with the in-situ observation and measurements. The simulation results from 3-D FEM shows good agreement with the data obtained from the measurements. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The findings obtained from two different types of numerical simulations can be used for the performance and safety assessment of nuclear waste disposal.

Journal Articles

Coupled thermo-mechanical simulations for HLW disposal tunnel using distinct element method

Shimizu, Hiroyuki; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Zairyo, 60(5), p.470 - 476, 2011/05

In this study, the thermal calculation algorism was newly developed and introduced to the original distinct element code, and the coupled thermo-mechanical behavior of rock mass around the HLW disposal tunnel was simulated. For the simulations, the experimental data was obtained from the pillar stability experiments with mechanical loading and heating at Aspo HRL (hard rock underground laboratory), Sweden and simulation results were compared with the measuring and observation results. The crack propagation process during heating can be successfully simulated and simulation results agree well with the measuring and observation results at the site. However, for the better agreement quantitatively, the further bonding parameter as a function of heat will be necessary.

Journal Articles

Discrete and continuum approaches for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository

Shimizu, Hiroyuki; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.248 - 253, 2011/01

This paper reports on the results of the numerical simulations for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository using Finite Element Method (FEM) and Distinct Element Method (DEM). The FEM approach provides quantitative information of the change of stress and strain during excavation and heating process. On the other hand, the DEM approach shows the crack propagation process at the borehole surface, and this result agrees qualitatively well with the experimental observation. By comparing these results obtained from both approaches, quantitative and qualitative insights into various aspects of the processes occurred in the near field can be obtained.

Journal Articles

Distinct element analysis for Class II behavior of rocks under uniaxial compression

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

International Journal of Rock Mechanics and Mining Sciences, 47(2), p.323 - 333, 2010/02

Journal Articles

Impacts of thermo-hydro-mechanical experiments on the microbial activity in compacted bentonite at the Kamaishi Mine, northeast Japan

Aoki, Kazuhiro; Sugita, Yutaka; Chijimatsu, Masakazu*; Tazaki, Kazue*

Applied Clay Science, 47(1-2), p.147 - 154, 2010/01

 Times Cited Count:1 Percentile:93.86(Chemistry, Physical)

Microbial activity has been investigated for the bentonite buffer and surrounding host rock (granodiorite) at Kamaishi Mine in Iwate. For the host rock, total number of bacteria and viable microorganisms were enumerated for deep groundwater in granodiorite. Presence of sulphate-reducing bacteria and denitrifying bacteria were also confirmed. The coupled thermo-hydro-mechanical (T-H-M) experiments named" engineered barrier experiments" were carried out to examine the in situ performance of buffer material. At the end of the heating and cooling phases, bentonite samples were taken for microbial analysis to determine if the naturally present microbial population in the buffer material survived the conditions in a simulated vault environment. The results confirmed the existence of heterotrophs, which disappeared in bentonite samples with low water content. These results suggest that microbial activity is severely limited near waste container in the vault for some time after disposal, due to desiccation as a result of the heat output of the waste container. Such knowledge will be useful in assessing the potential effects of microbial activity on deep geological disposal of high level radioactive waste.

Journal Articles

Assessing the long-term behavior of a radioactive waste disposal tunnel with a damage model incorporating chemical degradation effects

Kobayashi, Akira*; Chijimatsu, Masakazu*; Fujita, Tomoo; Yamamoto, Kiyohito*

Proceedings of 3rd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2008), p.621 - 628, 2008/06

To examine the effect of the degradation of rock on the behavior of near field of the repository of high-level radioactive waste disposal, the degradation of rock was examined by submerging the rock sample into saline water for 90 days. By using the damage parameters obtained from the degraded sample, the behavior of the near field was simulated with the varying boundary conditions for one million years. The model used for the analysis was called the damage expansion model considering the volumetric expansion due to damage. It was observed from the analyzed results that the damage would be developed locally at the spring line and crown of repository tunnel. After about one hundred years, the damage evolution would be finished even if the degradation progressed so much.

Journal Articles

Hydraulic modelling of unsaturated zones around three openings at the argillaceous Tournemire site (France)

Uehara, Shinichi*; Kobayashi, Akira*; Chijimatsu, Masakazu*; Onishi, Yuzo*; Fujita, Tomoo; Rejeb, A.*

Proceedings of 3rd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2008), p.419 - 425, 2008/06

Journal Articles

Influence of excavation of disposal tunnel on the near-field coupled thermal, hydraulic and mechanical phenomena

Chijimatsu, Masakazu*; Tsukada, Yasuhiro*; Kobayashi, Akira*; Fujita, Tomoo

Proceedings of 3rd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2008), p.381 - 390, 2008/06

Journal Articles

Development of stress conditions around a tunnel excavated in argillaceous rock related to change of saturation conditions

Uehara, Shinichi*; Kobayashi, Akira*; Chijimatsu, Masakazu*; Onishi, Yuzo*; Fujita, Tomoo

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.738 - 743, 2006/05

This paper reports the results of calculations about coupled hydro-mechanical process in the domain around excavations at clay rock site at Tournemire, France. We operated the numerical modelling by using a Finite Element Method code named THAMES, on the assumption that swelling pressure is parallel to saturation ratio. The results of modelling indicated that saturation ratio changes seasonally at the domain within several tens cm from tunnel wall. This extension is similar to that of damage zone observed in the tunnel at Tournemire site in 1881, which supports the idea that the saturation-desaturation cycles has decreased the rock strength and caused damage zone extension. The modelling results also suggested that the consideration of swelling pressure could affect evolution of stress state abruptly.

Journal Articles

Model calibration of small and large-scale laboratory THM experiments of the MX-80 bentonite

Chijimatsu, Masakazu*; B$"o$rgesson, L.*; Fujita, Tomoo; Hernelind, J.*; Jussila, P.*; Nguyen, T. S.*; Rutqvist, J.*; Jing, L.*

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.254 - 260, 2006/05

In Task A of DECOVALEX-THMC, five research teams study the influence of THM coupling on the safety of the near-field of a typical geological repository for high-level radioactive waste. In order to refine the analyses, the teams calibrated their models with laboratory experiments, including: swelling pressure tests, water uptake tests, thermally gradient tests, and the CEA mock-up THM experiment. This paper describes the mathematical models used by the teams, and compares the results of their calibration with the experimental data.

Journal Articles

Influence of coupled THM phenomena on the safety of a spent fuel repository; A Near-field study

Nguyen, T. S.*; B$"o$rgesson, L.*; Chijimatsu, Masakazu*; Fujita, Tomoo; Hernelind, J.*; Jussila, P.*; Rutqvist, J.*; Jing, L.*

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.141 - 149, 2006/05

In order to demonstrate the feasibility of geological disposal of spent CANDU fuel in Canada, a safety assessment was performed for a hypothetical repository in the Canadian Shield. The assessment shows that such repository would meet international criteria for dose rate; however, uncertainties in the assumed evolution of the repository were identified. Such uncertainties could be resolved by the consideration of coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes. In Task A of the DECOVALEX-THMC project, THM models will be refined and used to perform near-field simulations of the evolution of the repository in order to address the above uncertainties. This paper presents the definition and rationale of Task A and the preliminary results.

Journal Articles

Changes in intact rock damage parameters due to chemical effects and their influence on failure phenomena

Kobayashi, Akira*; Yamamoto, Kiyohito*; Aoyama, Shigeyasu*; Chijimatsu, Masakazu*; Fujita, Tomoo

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.281 - 286, 2006/05

To investigate the effect of the chemical degradation on the mechanical behavior, the rock samples preserved in the 10 % salt water and distilled water for 90 days are subjected to the unconfined compression test. The rock samples were obtained from $"A$sp$"o$ HRL in Sweden. The damage parameters were identified from the unconfined compression tests for two types of rock samples. Beforehand, the characteristics of the effect of each damage parameter on the mechanical behavior were investigated by numerical simulation. By investigating the change in the damage parameters of the chemically degraded rock, the effect of the chemical degradation was tried to infer through the results of parametric study. Moreover, the 3-D finite element simulation was carried out to examine the effect of change in the damage parameters due to chemical effect in detail.

Journal Articles

Development on computer system of the coupled thermo-hydro-mechanical and chemical process in the near-field of the high-level radioactive waste repository

Fujita, Tomoo; Fujisaki, Kiyoshi; Suzuki, Hideaki*; Kawakami, Susumu; Yui, Mikazu; Chijimatsu, Masakazu*; Neyama, Atsushi*; Ishihara, Yoshinao*; Hishiya, Tomoyuki*

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.416 - 421, 2006/00

We have initiated a research on the coupled Thermo-Hydro-Mechanical-Chemical (THMC) processes and are trying to carry out numerical experiments on the coupled THMC processes in order to predict the near-field long-term evolution. This paper describes the modified THMC model to add on the function of de-gases and gases diffusion, accumulation and dilution phenomena for mass transport analysis, and of ionic exchange, surface reaction and kinetic reaction for geochemical analysis. And also the results of demonstration study with THMC code are shown.

JAEA Reports

Study on the Monitoring Methods for Engineered Barriers Performance Confirmation (II)

Chijimatsu, Masakazu*; Fukudome, Kazuto*; Urano, Kazuhiko*; Imai, Hisashi*; Sasaki, Hajime*; Amemiya, Kiyoshi*

JNC-TJ8400 2004-027, 87 Pages, 2005/02

JNC-TJ8400-2004-027.pdf:2.13MB

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.

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