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Sugita, Yutaka; Ono, Hirokazu; Beese, S.*; Pan, P.*; Kim, M.*; Lee, C.*; Jove-Colon, C.*; Lopez, C. M.*; Liang, S.-Y.*
Geomechanics for Energy and the Environment, 42, p.100668_1 - 100668_21, 2025/06
The international cooperative project DECOVALEX 2023 focused on the Horonobe EBS experiment in the Task D, which was undertaken to study, using numerical analyses, the thermo-hydro-mechanical (or thermo-hydro) interactions in bentonite based engineered barriers. One full-scale in-situ experiment and four laboratory experiments, largely complementary, were selected for modelling. The Horonobe EBS experiment is a temperature-controlled non-isothermal experiment combined with artificial groundwater injection. The Horonobe EBS experiment consists of the heating and cooling phases. Six research teams performed the THM or TH (depended on research team approach) numerical analyses using a variety of computer codes, formulations and constitutive laws.
Wilson, J.*; Sasamoto, Hiroshi; Tachi, Yukio; Kawama, Daisuke*
Applied Clay Science, 275, p.107862_1 - 107862_15, 2025/05
Times Cited Count:0High-Level Radioactive Waste (HLW) repositories include iron or steel-based containers/overpack and bentonite buffers. Over the last 25 years or so, research efforts have attempted to elucidate the nature of iron-bentonite interactions, especially the potential for the deleterious alteration of the swelling clay component (smectite), to iron-rich layer silicates, some of which lack the capacity for intracrystalline swelling. This could result in a reduction or loss in swelling pressure in the bentonite buffer which is designed to protect waste containers from shear forces and also acts to restrict water and solute transport, as part of an engineered barrier system. Most data on iron-bentonite interactions come from experimental and geochemical modelling studies, as natural analogue data are lacking. The data suggests that there is the potential for the development of an iron-rich bentonite alteration zone with smectite (generally present as the aluminous montmorillonite type) undergoing alteration to iron-rich solids, including layer silicates and steel corrosion products such as green rust or magnetite. The evidence available is complex, arguably incomplete, with many potential complex couplings. Many uncertainties remain despite efforts taken over the last 25 years, but plausible scenarios for iron-bentonite interactions have been identified and possible implications for buffer properties have been suggested.
Taniguchi, Takumi; Matsumoto, Saori; Hiraki, Yoshihisa; Sato, Junya; Fujita, Hideki*; Kaneda, Yoshihisa*; Kuroki, Ryoichiro; Osugi, Takeshi
JAEA-Review 2024-059, 20 Pages, 2025/03
The basic performance required for solidifying waste into cement, such as fluidity before curing and strength after curing, is expected to be affected by the chemical effects of substances and components contained in the waste. The fluidity before curing and the strength properties after curing are greatly influenced by the curing speed of the cement. We investigated existing knowledge with a focus on chemical substances that affect the curing speed of cement. In this report, chemical substances that affect fluidity are broadly classified into inorganic substances such as (1) anion species, (2) metal elements such as heavy metals, (3) inorganic compounds as cement admixtures, and (4) organic compounds as cement admixtures. Based on the investigation, we actually added chemicals and measured the setting time. As a result, it was found that there are multiple mechanisms contributing to accelerated hardening. We investigated chemical substances that inhibit the curing reaction of cement, and were able to compile information to consider ingredients that are contraindicated in cement curing.
Metcalfe, R.*; Benbow, S. J.*; Kawama, Daisuke*; Tachi, Yukio
Science of the Total Environment, 958, p.177690_1 - 177690_17, 2025/01
Uplifting fractured granitic rocks occur in substantial areas of countries such as Japan. A repository site would be selected in such an area only if it is possible to make a safety case, accounting for the changing conditions during uplift. The safety case must include robust arguments that chemical processes in the rocks around the repository will contribute sufficiently to minimise radiological doses to biosphere receptors. To provide confidence in the safety arguments, numerical models need to be sufficiently realistic, but also parameterised conservatively (pessimistically). However, model development is challenging because uplift involves many complex couplings between groundwater flow, chemical reactions between water and rock, and changing rock properties. The couplings would affect radionuclide mobilisation and retardation, by influencing diffusive radionuclide fluxes between groundwater flowing in fractures and effectively immobile porewater in the rock matrix and radionuclide partitioning between water and solid phases, via: (i) mineral precipitation/dissolution; (ii) mineral alteration; and (iii) sorption/desorption. It is difficult to represent all this complexity in numerical models while showing that they are parameterised conservatively. Here we present a modelling approach, illustrated by simulation cases for some exemplar radioelements, to identify realistically conservative process conceptualisations and model parameterisations.
Metcalfe, R.*; Tachi, Yukio; Sasao, Eiji; Kawama, Daisuke*
Science of the Total Environment, 957, p.177375_1 - 177375_17, 2024/12
A safety case for an underground radioactive waste repository must show that groundwater will not in future transport radionuclides from the repository to the near-surface environment (the biosphere) in harmful quantities. Safety cases are developed step-wise throughout a programme to site and develop a repository. At early stages, before a site is selected, safety cases are generic and based on simplified safety assessment models of the disposal system that have conservative parameter values. Later, when site-specific conditions are known, more realistic models are needed for the long-term geo-environmental evolution and their impacts on radionuclide migration/retention. Uplift is one such environmental change, which may be particularly important in countries near active tectonic plate boundaries, such as Japan. Here we review the state of knowledge about how the properties of fractured granitic rocks evolve during uplift, based on studies in Japan. Hence, we present conceptual models and a generic scenario for mass transport and retardation processes in uplifting granitic rocks as a basis for realistic numerical models to underpin safety assessment.
Walker, C. S.*; Arthur, R. C.*; Anraku, Sohtaro; Sasamoto, Hiroshi; Mihara, Morihiro
Applied Geochemistry, 175, p.106086_1 - 106086_17, 2024/11
Times Cited Count:0 Percentile:0.00(Geochemistry & Geophysics)The thermodynamic properties and revised Helgeson-Kirkham-Flowers equation of state (r-H-K-F EoS) parameters of the hydrated (Si(OH)(aq), SiO(OH)
and SiO
(OH)
) and fictive dehydrated (SiO
(aq), HSiO
and SiO
) monomeric silicon species are used extensively to describe the pH, composition, temperature, and pressure dependence of formation/breakdown reactions of all silicon-bearing compounds globally. Experimental log10 equilbrium constant, K values describing the formation reactions of the hydrated and dehydrated monomeric silicon species were therefore compiled from the literature, extrapolated to zero ionic strength by specific ion interaction theory as required and used to derive their thermodynamic properties and r-H-K-F EoS parameters. Consideration of all formation reactions in the same study provides a collective, internally consistent update to the thermodynamic properties and r-H-K-F EoS parameters of the monomeric silicon species that can provide a satisfactory match to the experimental log10 K values at
= 0.01-600
C,
= 1-3000 bars,
= 0.35-1.1 g cm
, and zero ionic strength. These temperature and pressure limits comfortably bracket t=0.01-100
C and P =1-270 bars relecant to the geological disposal of radioactive wastes at depths of up to 1 km.
Takayama, Yusuke; Sato, Daisuke*; Sugita, Yutaka
Kansai Geo-Symposium 2024; Chikasui Jiban Kankyo, Bosai, Keisoku Gijutsu Ni Kansuru Shinpojiumu Rombunshu, p.115 - 119, 2024/11
During the initial phases after closure of a high-level radioactive waste repository, the temperature of the buffer material will increase. Therefore, fundamental properties regarding the temperature dependence of bentonite, which is the main material of the buffer material, have been tested. The number of tests for the temperature dependence of displacement behavior is less than the number of tests for the temperature dependence of swelling pressure and permeability. In this paper, two tests were conducted using a consolidation test device that can control temperature conditions. One is a cyclic loading and unloading test under temperature conditions from room temperature to 80 C. The second is a temperature rise and fall test from room temperature to 80
C under stable loading condition. It was clarified that large deformations occur in the specimen under high temperature conditions, that the deformation associated with temperature changes is affected by the past stress path, and that irreversible deformation occurs under normal consolidation conditions.
Hanamachi, Yuji*; Walker, C.*; Anraku, Sohtaro; Sasamoto, Hiroshi
NIMS Bisai Kozo Kaiseki Purattohomu Riyo Hokokusho (Internet), 4 Pages, 2024/10
no abstracts in English
Sugiura, Yuki; Ishidera, Takamitsu; Aoyagi, Noboru; Mei, H.; Saito, Takumi*; Tachi, Yukio
Applied Clay Science, 258, p.107476_1 - 107476_10, 2024/09
Times Cited Count:2 Percentile:51.28(Chemistry, Physical)Ito, Shinji*; Shimizu, Hiroyuki*; Ono, Shintaro*; Takayama, Yusuke
Doboku Gakkai Rombunshu (Internet), 80(8), p.24-00030_1 - 24-00030_18, 2024/08
In the design consideration of a geological disposal facility for radioactive waste, it is essential to perform a mechanical evaluation that takes into account phenomena that may occur from construction and operation to post-closure. With this background, we have developed the long-term mechanical analysis system MACBECE. In this research, we have built an analysis system that can consistently evaluate the mechanical behavior considering the thermal and hydraulic evolution after the closure of the repository by incorporating the constitutive model for unsaturated soils and coupling with the thermal-hydraulic analysis. As a validation, a mechanical analysis was conducted for the in-situ experiment for full-scale engineered barrier system performance experiment at Horonobe URL. Despite some discrepancies due to constraints in two-dimensional analysis, the extended functionality of the analysis code was confirmed to effectively repro-duce the measured data.
Kimuro, Shingo; Taneichi, Yayoi; Iwata, Hajime; Ishidera, Takamitsu; Kitamura, Akira; Tachi, Yukio; Tanaka, Takeru*; Hirano, Kana*; Hieda, Manami*; Miyabe, Shunsuke*; et al.
Journal of Solution Chemistry, 53(6), p.854 - 868, 2024/06
Times Cited Count:0 Percentile:0.00(Chemistry, Physical)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.
Yuan, X.*; Hu, Q. H.*; Fang, X.*; Wang, Q. M.*; Ma, Y.*; Tachi, Yukio
Sedimentary Geology, 465, p.106633_1 - 106633_14, 2024/05
Times Cited Count:0 Percentile:0.00(Geology)Yamaguchi, Masaaki; Suzuki, Yuji*; Kabasawa, Satsuki; Kato, Tomoko
JAEA-Data/Code 2024-001, 21 Pages, 2024/03
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.
Saito, Yuki*; Ishiwata, Tobimaru*; Horiuchi, Misato*; Nishiki, Yuto*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro; Sato, Tsutomu*
Shigen, Sozai Koenshu (Internet), 11(1), 7 Pages, 2024/03
no abstracts in English
Hanamachi, Yuji*; Walker, C.*; Sasamoto, Hiroshi; Mihara, Morihiro
NIMS Bisai Kozo Kaiseki Purattofuomu Riyo Hokokusho (Internet), 2 Pages, 2023/12
A High-volume Fly ash Silica fume Cement (HFSC) has been considered as the use of concrete support of drift in deep disposal of radioactive wastes. JAEA has been carried out experiments and modeling studies to evaluate chemical stability of C-A-S-H gel synthesized which would be believed as the dominant component of the HFSC. For the modeling purpose, it is necessary to evaluate the chemical composition both of C-A-S-H gel synthesized and accompanied minerals in the experiment. In the year of 2020, Al and
Si NMR measurement were performed to identify Al and Si distribution in the sample and chemical composition of C-A-S-H gel was derived. However, it was impossible to derive the C-A-S-H gel composition having the expected Al/Si molar ratio since there were several accompanied minerals produced in the experiment due to the short term of immersion. This time similar approach to derive C-A-S-H gel composition is adopted using NMR measurement for the sample of longer time (6 months).
Soler, J. M.*; Kekl
inen, P.*; Pulkkanen, V.-M.*; Moreno, L.*; Iraola, A.*; Trinchero, P.*; Hokr, M.*;
ha, J.*; Havlov
, V.*; Trpko
ov
, D.*; et al.
Nuclear Technology, 209(11), p.1765 - 1784, 2023/11
Times Cited Count:4 Percentile:73.39(Nuclear Science & Technology)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
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.
Takayama, Yusuke; Yamamoto, Yoichi*; Goto, Takahiro*
Jiban Kogaku Janaru (Internet), 18(3), p.317 - 330, 2023/09
It has been reported that the deformation greatly increased in the secondary consolidation process in the past long-term consolidation test of 1.8 years on Na-type bentonite/sand mixed soil. Therefore, we analyzed potential contributing factors in this behavior. A long-term consolidation test for about 10 years on bentonite and kaolinite was started using the test equipment with countermeasures against these factors. In this paper, the secondary consolidation behavior of bentonite was investigated based on the long-term consolidation test data for 2.7, 3.7 and 4 years. The results were generally consistent with the conventional findings on soil mechanics that the deformation due to secondary consolidation progresses linearly with respect to logarithm of time. This test will be continued for about 10 years and longer-term secondary consolidation behavior will be investigated.