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Journal Articles

A Systematic radionuclide migration parameter setting approach for potential siting environments in Japan

Hamamoto, Takafumi*; Ishida, Keisuke*; Shibutani, Sanae*; Fujisaki, Kiyoshi*; Tachi, Yukio; Ishiguro, Katsuhiko*; McKinley, I. G.*

Proceedings of 2019 International High-Level Radioactive Waste Management Conference (IHLRWM 2019) (USB Flash Drive), p.77 - 82, 2019/04

Journal Articles

Assessment of sorption and diffusion in the rock matrix in the NUMO safety case

Hamamoto, Takafumi*; Shibutani, Sanae*; Ishida, Keisuke*; Fujisaki, Kiyoshi*; Yamada, Motoyuki*; Tachi, Yukio

Proceedings of 6th East Asia Forum on Radwaste Management Conference (EAFORM 2017) (Internet), 6 Pages, 2017/12

NUMO has developed a generic safety case to demonstrate the feasibility and safety of geological disposal of HLW and TRU in Japan and to provide a basic structure for the safety case which will be applicable to any potential site. In this safety case, the safety assessment was carried out for the repositories tailored to site descriptive models developed for three representative rock groups (plutonic, Neogene sedimentary and Pre-Neogene sedimentary rocks). Radionuclide migration parameters in rocks, i.e. distribution coefficients (Kds) and effective diffusion coefficients (Des), were derived to allow safety analysis for a range of scenarios. In this generic stage, the values of these parameter were given as the statistical values derived from laboratory data for certain rock types. The data were extracted from the latest database, with interpretation based on radionuclide speciation derived from relevant groundwater thermodynamic modelings.

Journal Articles

Engineered barrier experiments and analytical studies on coupled thermal-hydraulic-chemical processes in bentonite buffer material

Suzuki, Hideaki; Fujisaki, Kiyoshi*; Fujita, Tomo

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 16(1), p.43 - 56, 2009/12

The numerical analysis model was developed that understand the coupled thermal - hydraulic - mechanical - chemical (THMC) processes in the near field of high-level radioactive waste (HLW) repository after emplacement of the engineered barrier system (EBS). This paper is focusing on measured data of the experiments and calculated results of the THC model which were carried out for the period of 830 days. It was found that the information about the geochemical reaction and the mass transfer in the buffer material was obtained; pH distribution of pore water, precipitation of the secondary mineral etc. It was also indicated that the temperature and water content in the buffer material and mineral dissolution/precipitation in a contact surface of buffer material and mortar could be represented by the developed numerical model.

JAEA Reports

Developing confidence in a coupled TH model based on the results of experiment by using engineering scale test facility, "COUPLE"

Fujisaki, Kiyoshi; Suzuki, Hideaki; Fujita, Tomo

JAEA-Research 2008-020, 62 Pages, 2008/03

JAEA-Research-2008-020.pdf:24.3MB

In evaluating the behavior of near-field after emplacement of engineered barriers, it is necessary to understand quantitative changes of near-field over time and space. However, the coupled phenomena in near-field are complicated because thermo-, hydro-, mechanical, chemical process will interact, so that no comparison with real behavior will make it possible to find out if the applied model will represent the coupled behavior adequately or not. Hence, it is necessary to validate the model, based on the result of coupled behavior experiment in laboratory or in site. In this report, authors evaluated the applicability of coupled T-H model under the condition of simulated near-field, based on the results of coupled experiment in room. As a result, it has shown that the model which improved the fit to the measured data, is reasonable under this condition.

JAEA Reports

Coupled hydro-transport analysis study of geochemical reaction due to unsaturated around the disposal tunnel; Application of the coupled Thermo-Hydro-Mechanical and Chemical (THMC) processes model/analysis code in the geological disposal for the high-level radioactive waste

Suzuki, Hideaki; Fujisaki, Kiyoshi; Fujita, Tomo

JAEA-Research 2008-003, 48 Pages, 2008/03

JAEA-Research-2008-003.pdf:2.07MB

The development of excavation disturbed zone (EDZ) around the disposal tunnel affects such as the corrosive environment of the over-pack and environmental condition of the nuclear species migration on the geological disposal for the high-level radioactive waste (HLW). It is necessary to consider aftermath of EDZ in initial condition of the realistic numerical simulation of the long-term behavior of near-filed HLW repository after emplacement of engineered barrier system. This report presents the analysis assessment geochemical reaction with the development of the unsaturated zone around the disposal tunnel by developed the coupled Thermo-Hydro-Mechanical and Chemical (THMC) processes model / analysis code. As a result, the THMC processes analysis model apply a change of the solution composition by degasification of the carbon dioxide gas to the pore water and the change of the oxidation-reduction potential due to unsaturated zone around the disposal tunnel.

JAEA Reports

Study on simulation of salt accumulation (Joint research)

Fujita, Tomo; Yui, Mikazu; Suzuki, Hideaki*; Fujisaki, Kiyoshi; Sazarashi, Masami*

JAEA-Research 2007-017, 47 Pages, 2007/03

JAEA-Research-2007-017.pdf:9.27MB

This report describes the results of a joint research entitled "Study on Simulation of Salt Accumulation" which was conducted under the collaboration between the Institute of Research and Innovation and the Japan Atomic Energy Agency. In the experiments for salt accumulation, accumulation of ${it Na$_{2}$SO$_{4}$}$ and ${it CaSO$_{4}$}$ was observed near the heater surface. Based on the facts from experiments, we have made hypothesis for mechanism of salt accumulation, and developed the model for it. Then, we conducted numerical simulations for salt accumulation phenomena under the saturated condition using the geochemical code "PHREEQC". It became clear that salt accumulation behavior can be evaluated qualitatively from these simulations, but quantitative evaluation requires more realistic modeling. Moreover we evaluated salt accumulation phenomena by simulations using coupled thermo - hydro - mechanical and chemical model / code assuming the unsaturated and / or saturated condition. A series of simulations were conducted focusing on accumulation of gypsum, and the result showed that tendency of salt accumulation phenomena was in agreement with that of experiments, but the profile of distribution of accumulated gypsum was not in agreement. In conclusion, it became clear that more realistic boundary condition should be considered and problems on coupled model / code were identified for further study.

Journal Articles

Experimental studies on the coupled THMC processes by couple equipment

Fujisaki, Kiyoshi; Suzuki, Hideaki*; Fujita, Tomo; Ito, Akira*; Oda, Yoshihiro

Proceedings of 2nd International Conference on Coupled T-H-M-C Processes in Geo-systems; Fundamentals, Modeling, Experiments and Applications (GeoProc 2006), p.213 - 219, 2006/05

An important part of the safety assessments of near field in a geological disposal system of high-level radioactive waste consists an assessment of the coupled thermal-hydraulic-mechanical and chemical (THMC) phenomena. In order to validate the newly developed THMC model, the engineered scale experimental studies on the coupled THMC processes by COUPLE equipment have been carried out with a simulated engineered barrier surrounded by a mortar block. In this experiment, temperature at heater and side surface of mortar block was controlled at constant temperature, respectively. And high-pH water reacted with mortar infiltrates into the buffer material. This paper presents the results of measured data by various sensors during the experiment and sampling data of pH and leaching cations in buffer material after the experiment, in COUPLE equipment. And also the results of preliminary simulations on coupled T-H processes and chemical process in the experiment are described.

Journal Articles

Study of long-term behavior of engineered and geological barrier system

Aoyanagi, Shigeo; Oda, Yoshihiro; Sasamoto, Hiroshi; Shibata, Masahiro; Tanai, Kenji; Taniguchi, Naoki; Nishimura, Mayuka; Fujisaki, Kiyoshi; Kikuchi, Hirohito*; Matsumoto, Kazuhiro*

Hoshasei Haikibutsu Anzen Kenkyu Nenji Keikaku (Heisei-13-Nendo$$sim$$Heisei-17-Nendo) Kenkyu Seika Hokokushu, p.179 - 203, 2006/03

no abstracts in English

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, Tomo; 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.

Oral presentation

Coupled Thermo-Hydro-Mechanical and Chemical (THMC) process analysis COUPLE equipment

Suzuki, Hideaki*; Fujisaki, Kiyoshi; Fujita, Tomo; Yui, Mikazu

no journal, , 

The research for numerical experiments on the coupled Thermo-Hydro-Mechanical and Chemical (THMC) process in the near-field of a high-level radioactive waste repository has been initiated, in order to understand and predict the near-field long-term evolution. As a part of this research, the engineered scale experimental studies on the coupled THMC processes by COUPLE equipment have been carried out. The simulation of COUPLE equipment was carried out in order to verify THMC analysis code. As a result, the geochemical reaction of buffer material was a precipitation reaction of calcite, and the analysis result of temperature distribution, re-wetting and pore water pH of buffer material were in agreement with the experimental result.

Oral presentation

Case study development on the coupled Thermo-Hydro-Mechanical and Chemical (THMC) process, 2; Demonstration analisys for near field of HLW repository

Suzuki, Hideaki; Fujisaki, Kiyoshi; Fujita, Tomo; Naito, Morimasa; Yui, Mikazu

no journal, , 

The expected processes in the near-filed of a High-Level Radioactive (HLW) repository after emplacement of engineered barrier system are the coupled Thermo-Hydro- Mechanical and Chemical (THMC) processes. In order to validate the newly developed THMC model, the engineered scale experiment studies on the coupled THMC processes by COUPLE equipment have been carried out with a simulated engineered barrier. This paper presents the result of simulation on couple THC process in the COUPLE experiment and case study analysis for near field of HLW repository.

Oral presentation

Model development on the coupled Thermo-Hydro-Mechanical and Chemical (THMC) process, 1; Validation of coupled T-H model based on the results of in-room experiment

Fujisaki, Kiyoshi; Suzuki, Hideaki; Fujita, Tomo; Naito, Morimasa; Yui, Mikazu

no journal, , 

Near a high-level radioactive waste repository after emplacement of engineered barriers, coupled thermo-, hydro-, mechanical, and chemical (T-H-M-C) processes will occur. To predict these phenomena quantitatively and improve reliability in assessing the design and the long term performance of engineered barriers, JAEA has developed a coupled thermo-, hydro-, mechanical, and chemical (T-H-M-C) analysis model / code. In this report, authors evaluated the applicability of coupled T-H model under the condition of simulated near-field, based on the results of in-room coupled experiment. As a result, it has shown that the model which improved the fit to the measured data, is reasonable under this condition.

Oral presentation

Coupled hydro-transport analysis study on geochemical environmental change caused by tunnel excavation using geological data obtained from the Horonobe URL project

Suzuki, Hideaki; Fujita, Tomo; Fujisaki, Kiyoshi*

no journal, , 

The development of excavation disturbed zone (EDZ) around the disposal tunnel affects such as the corrosive environment of the over-pack and environmental condition of the nuclear species migration on the geological disposal for the high-level radioactive waste (HLW). It is necessary to consider affect of EDZ in the realistic numerical simulation of the long-term behavior of near-filed HLW repository after emplacement of engineered barrier system. This study presents the results on the analysis assessment on geochemical reaction with the evolution of the unsaturated zone around the tunnel with consideration of Horonobe area geological environment, using the developed coupled Thermo-Hydro-Mechanical and Chemical (THMC) processes analysis model. As a result, this model is applied a change of the solution composition by degasification of the carbon dioxide gas to the pore water and the change of the oxidation-reduction potential due to unsaturated zone around the tunnel.

Oral presentation

Application tests of the sensor for measurement of water content in the buffer material

Nakama, Shigeo; Fujisaki, Kiyoshi*; Suzuki, Hideaki; Fujita, Tomo; Chijimatsu, Masakazu*

no journal, , 

no abstracts in English

Oral presentation

Development of simulation technology for salt condensation and segregation in compacted bentonite

Nagatani, Mutsumi; Fujisaki, Kiyoshi*; Sazarashi, Masami; Fujita, Tomo; Chijimatsu, Masakazu*

no journal, , 

no abstracts in English

Oral presentation

The Project for grouting technology development for the high level radioactive waste repository, 11; Development of assessment technology for grouting effects

Sasamoto, Hiroshi; Yui, Mikazu; Naito, Morimasa; Walker, C.; Fujisaki, Kiyoshi*; Takase, Hiroyasu*

no journal, , 

Development of a method to evaluate applicability of cementitious materials based on the implications for long-term safety has been performed considering the use of cementitious grout materials for reduction of water leakage during the stages of drilling of drift and implementation. In this study, an approach to evaluate the effects on alteration behavior of rock, the status of development of necessary model and database and a test case for evaluation are presented.

Oral presentation

Effect of interaction between carbon steel and simulated glass on glass dissolution behavior

Goto, Takahiro*; Matsubara, Ryuta*; Hamamoto, Takafumi*; Fujisaki, Kiyoshi*; Mitsui, Seiichiro; Taniguchi, Naoki

no journal, , 

For the purpose of improvement of long-term glass corrosion model, we conducted immersion tests with specimens of carbon steel and simulated waste glass at 50$$^{circ}$$C and 80$$^{circ}$$C under nitrogen gas atmosphere. We also conducted control immersion tests with a specimen of carbon steel or simulated waste glass under the same conditions. After the immersion tests, we determined glass corrosion rates and secondary phases on the surface of carbon steel specimen. Glass corrosion rates for the immersion tests with specimens of carbon steel and simulated waste glass were three times larger than those for the control immersion tests with simulated waste glass specimen. With X-ray diffraction, several peaks associated with an iron silicate mineral were identified. This observation is consistent with the results of geochemical calculation based on solution data and published study using carbon steel and simulated waste glass.

Oral presentation

Corrosion behavior of simulated high-level waste glass in the presence of carbon steel

Goto, Takahiro*; Matsubara, Ryuta*; Hamamoto, Takafumi*; Fujisaki, Kiyoshi*; Mitsui, Seiichiro; Taniguchi, Naoki

no journal, , 

To improve long-term glass corrosion model, immersion tests with specimens of carbon steel and simulated waste glass were conducted at 50$$^{circ}$$C and 80$$^{circ}$$C under nitrogen gas atmosphere for 131 days. Control tests with a specimen of carbon steel or glass under the same conditions were also conducted. After the tests, the element concentration in the solution was analyzed to determine glass corrosion rates. We also analyzed the surface of specimens with XRD and TEM/ED (electron diffraction)/EDX to identify secondary phases. Glass corrosion rates for the tests with specimens of carbon steel and glass were two times larger than those for the control tests with glass specimen. With XRD and TEM/ED/EDX, we determined iron silicates on the surface of both carbon steel and glass. These observations are consistent with the results of geochemical calculation and published studies. The results indicate that glass corrosion could be enhanced by the precipitation of iron silicates.

Oral presentation

Diffusion behavior of iodide and cesium ions in hardened cement paste

Kawato, Takaya*; Ishida, Keisuke*; Yamamoto, Takeshi*; Minato, Daisuke*; Fujisaki, Kiyoshi*; Hamamoto, Takafumi*; Mihara, Morihiro

no journal, , 

no abstracts in English

Oral presentation

Progress of R&D for geological disposal of vitrified waste

Matsubara, Ryuta*; Fujisaki, Kiyoshi*; Ishida, Keisuke*; Ishiguro, Katsuhiko*; Inagaki, Yaohiro*; Okubo, Takahiro*; Mitsui, Seiichiro; Iwata, Hajime; Sekine, Nobuyuki*

no journal, , 

Restriction of radionuclide release by low dissolution rate is expected for the vitrified waste as a one of safety functions of the geological disposal system. In order to assess the performance of vitrified waste, it is important to understand how its safety function works under the environmental condition of a deep geological repository. This presentation provides the recent progress on the R&D to improve the current understanding of the key processes affecting glass dissolution rate and the predictive modeling of long-term behavior of the vitrified waste.

Oral presentation

R&D program of operational model of long-term performance for vitrified high-level radioactive waste

Matsubara, Ryuta*; Fujisaki, Kiyoshi*; Ishida, Keisuke*; Ishiguro, Katsuhiko*; Inagaki, Yaohiro*; Okubo, Takahiro*; Mitsui, Seiichiro; Iwata, Hajime; Sekine, Nobuyuki*

no journal, , 

Since the performance of vitrified High-level Radioactive Waste depends on thermal, hydraulic, mechanical, and chemical (THMC) conditions, NUMO, as the implementer of geological disposal, has been promoting R&D of operational model the long-term performance of vitrified High-level Radioactive Waste in consideration of THMC conditions. NUMO has identified R&D issues regarding the glass dissolution and planed the R&D program through FEP (Features, Events, and Processes) analysis and parametric study with numerical model to evaluate relative importance of relevant processes. At present, three R&D programs are ongoing as joint researches with JAEA and two universities: long term glass dissolution experiment to understand evolution of glass dissolution kinetics, glass dissolution experiment at various environmental conditions to assess the performance under several potential repository conditions with the time evolution, and molecular dynamics simulation to understand elemental migration at the interface between glass surface and groundwater. The current status of R&D programs will be introduced in this presentation.

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