Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio
Applied Clay Science, 195, p.105741_1 - 105741_11, 2020/09
Safety functions for the clay buffer in a repository for high-level radioactive waste (HLW) are fulfilled if the presence of montmorillonite with high swelling capacity and low permeability is maintained in the long-term. The transformation of montmorillonite to the non-swelling mineral likely illite is addressed in most safety assessments by using simple semi-empirical kinetic models, but this approach contrasts with more complex reactive-transport simulations. In the present study, reactive-transport simulations are compared with simple semi-empirical kinetic models. Results suggest that reactive-transport simulations err on the side of conservatism, but may produce unrealistic estimates of illitization. This comparison demonstrates that reactive-transport models may be carefully applied to simulate the long-term evolution of near field environment for HLW disposal.
Nakayama, Masashi; Saiga, Atsushi; Kimura, Shun; Mochizuki, Akihito; Aoyagi, Kazuhei; Ono, Hirokazu; Miyakawa, Kazuya; Takeda, Masaki; Hayano, Akira; Matsuoka, Toshiyuki; et al.
JAEA-Research 2019-013, 276 Pages, 2020/03
The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The present report summarizes the research and development activities of these 3 important issues carried out during 3rd Medium to Long-term Research Phase.
Miyakawa, Kazuya; Mezawa, Tetsuya*; Mochizuki, Akihito; Sasamoto, Hiroshi
JAEA-Data/Code 2020-001, 41 Pages, 2020/03
Development of technologies to investigate properties of deep geological environment and model development of geological environment have been pursued in "Geoscientific Research" in the Horonobe Underground Research Laboratory (Horonobe URL) project. A geochemical model which is a part of geological environment model requires the data of groundwater chemistry around the Horonobe URL for the development. This report summarizes the data obtained for 3 years from the fiscal year 2017 to 2019, especially for the results for measurement of physico-chemical parameters and analysis of groundwater chemistry, in the Horonobe URL project.
Mochizuki, Akihito; Ishii, Eiichi; Miyakawa, Kazuya; Sasamoto, Hiroshi
Engineering Geology, 267, p.105496_1 - 105496_11, 2020/03
The mechanical and hydraulic properties of rocks around mine drifts change significantly during the construction and operation of a radioactive-waste repository, with air intrusion causing the oxidation of rock and groundwater in excavation-damaged zones (EDZ). Redox conditions in such zones associated with niches excavated in mudstone at the Horonobe Underground Research Laboratory (URL), which is believed to be generally representative of conditions that could exist in the EDZ of a repository, were studied with the aim of improving our understanding of factors that control redox conditions in such rock-groundwater systems. Groundwater Eh values around the niches have reducing values of less than -150 mV. The SO concentration, regarded as an oxidation indicator, is consistently as low as 1 mol L. Gas occupies more than 50% of zone volumes, including CH and CO with traces of N and O. Cores drilled from host rock around a URL gallery were analyzed, with no pyrite dissolution or precipitation of calcium sulfates being found. It is concluded that oxidizing conditions do not exist in the excavation-damaged zones, which is attributed to the suppression of air intrusion by the release of CH and CO from groundwater as pressures decreased and their accumulation in fractures. The modeling of oxygen diffusion into host rock further indicates that a reducing environment is maintained around the URL drifts.
Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi
JAEA-Data/Code 2019-014, 56 Pages, 2020/02
Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Groundwater pressure and geochemical parameters such as pH and oxidation-reduction potential in the deep groundwater have been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the data of groundwater pressure which have been obtained by the monitoring systems installed at the 350 m gallery. The data obtained from April 1, 2016 until March 31, 2019 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.
Miyakawa, Kazuya; Aoyagi, Kazuhei; Sasamoto, Hiroshi; Akaki, Toshifumi*; Yamamoto, Hajime*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
The construction and operation of geological repositories require excavation and ventilation of galleries, with significant groundwater drainage. Desaturation of rock around galleries is unavoidable and may affect hydraulic properties and redox conditions. This study used numerical modeling to assess the influence of dissolved gas on the degree of saturation of rock surrounding excavated galleries, focusing on siliceous mudstone rock in the 140 m, 250 m, and 350-m-deep galleries of the Horonobe Underground Research Laboratory, Japan. Based on previous electrical survey, the degree of saturation in the 250 m gallery was higher than that in the 140 m and 350 m galleries. In the Horonobe area, deep groundwater contains high concentrations of dissolved methane, and exsolution of this methane from pore water can affect desaturation. Simple numerical modeling, including simulation of multiphase flows, was undertaken for each gallery to confirm the effect of dissolved gas and rock permeability on desaturation. A sensitivity analysis was performed by varying dissolved gas contents and permeability. Results indicate that the dissolved gas content affects both the degree of saturation and its spatial extent, whereas rock permeability affects only the latter. Higher dissolved gas concentrations result in lower degrees of saturation with a greater spatial extent of desaturation, and higher permeability leads to greater extents of desaturation. It is therefore likely that gas content, rather than rock permeability, caused the observed variations in the saturation degree.
Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio
Applied Clay Science, 179, p.105146_1 - 105146_10, 2019/10
Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability was evaluated. Thermodynamic modeling using three different TDBs shows that stability fields for montmorillonite exist from 0 to 140C, but at low values of silica activity, a stability field for illite replaces that for montmorillonite. Pore fluid chemical and mineralogical data for sediments from ODP sites from offshore Japan show a trend from montmorillonite + amorphous silica stability at temperatures up to 60C to that for illite + quartz at higher temperatures. However, even over very long timescales ( 1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80C.
Mochizuki, Akihito; Sasamoto, Hiroshi; Mezawa, Tetsuya*; Miyakawa, Kazuya
Chikasui Gakkai-Shi, 61(1), p.3 - 20, 2019/02
Redox potential of deep groundwater in the Horonobe area, Hokkaido, was measured, and uncertainty of the measurement and thermodynamic interpretation was evaluated. The redox potential of groundwater obtained using monitoring units in the Underground Research Laboratory ranged between -250 and -100 mV, and the effect of the excavation of drifts on the redox potential is considered to be small in spite of its temporal variation. The redox potential is controlled by the reaction of chemical pairs of SO/FeS, SO/HS and CO(aq)/CH(aq). The comparison between the equilibrium potential for these reactions and the measured redox potentials suggests that 50 mV of uncertainty for the measurement of the redox potential is appropriate.
Sasamoto, Hiroshi; Onda, Shingo*
Geological Society Special Publications, 482, 13 Pages, 2018/09
Colloid concentration is an important parameter in models of colloid-facilitated transport. The purpose of present study is to characterize colloid concentrations and colloid stability in natural groundwater from the Horonobe Underground Research Laboratory (URL) as for development of a procedure. The particle sizes of colloids in groundwaters from the Horonobe URL range from several nm to ca. 500 nm, with a mode particle size of ca. 120 nm. Evaluation of colloid stability by DLVO theory suggests that larger colloids (i.e., 100 nm in diameter) would be more stable than smaller colloids in some groundwaters. The estimated colloid particle concentrations ranged from 2.3310 to 1.1210 pt/mL, and mass concentrations were estimated to range from 45 to 1540 g/L for diameters greater than 100 nm. Colloids in Horonobe groundwaters appear to be less stable, with a moderate potential for transport, than colloids investigated in similar international studies. This reduced stability may be due to relatively higher ionic strengths and moderate dissolved organic concentrations in Horonobe groundwaters compared to their international counterparts.
Sasamoto, Hiroshi; Sato, Hisao*; Arthur, R. C.*
Journal of Geochemical Exploration, 188, p.318 - 325, 2018/05
Ammonium is potentially an important constituent of deep groundwater under reducing condition. The retention of cesium by sorption in geological formations may have an important role ensuring the long-term safety of high-level radioactive waste. Cesium sorption will be affected by competing effects due to dissolve cation likely ammonium in groundwater, however. In the present study, a possible reaction to control of ammonium in deep groundwater was evaluated based on the data selected in the Horonobe as a test case in Japan. Results of investigation of mineralogy, thermodynamic evaluation of groundwaters and the Electron Probe Micro Analysis (EPMA) to identify nitrogen distribution on minerals suggest that the clay minerals bearing potassium, particularly smectite, illite and interstratified illite/smectite, appear to control the ammonium concentration in groundwaters by ion exchange reactions. Additionally, the selected groundwaters in the Horonobe seem to resemble to the gas and oil fields groundwater in the screened dataset in Japan in terms of ammonium distribution.
Mezawa, Tetsuya; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi
JAEA-Data/Code 2018-001, 55 Pages, 2018/03
Japan Atomic Energy Agency has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Geochemical parameters of groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater has been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the physico-chemical parameters of groundwater which have been obtained by the monitoring systems installed at the 140 m, 250 m and 350 m gallery. The data obtained until March 31, 2017 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.
Nakata, Kotaro*; Hasegawa, Takuma*; Oyama, Takahiro*; Ishii, Eiichi; Miyakawa, Kazuya; Sasamoto, Hiroshi
Geofluids, 2018, p.7823195_1 - 7823195_21, 2018/01
A groundwater scenario is one of the scenario for safety assessment of geological disposal of high-level radioactive waste. In the safety assessment for groundwater scenario, the slow groundwater flow for a long-term should be an important factor. In the present study, study on stability of groundwater in the Koetoi and Wakkanai formations of Neogene marine based sedimentary rock at the Horonobe area, Hokkaido was performed by investigating the isotopes of chlorine and helium, and the stable isotopes of water. As the results, the stability of groundwater in deeper part of the Wakkanai formation was suggested due to no direct evidence of meteoric water intrusion during the uplift since ca. 1 Ma. Contrary, the groundwater both in the Koetoi formation and the upper Wakkanai formation would be unstable because the meteoric water intrusion was suggested by paleohydrogeological condition and the results of groundwater dating. Likely the Horonobe area, the accurate dating of groundwater would be difficult due to the complex effects of upward and mixing water derived from diagenesis in the thick sediment formation. However, a comparative procedure using both the results of groundwater dating and paleohydrogeological information would be useful for general evaluation of groundwater flow conditions for the long-term (i.e., check the possibility for long-term stability of groundwater).
Miyakawa, Kazuya; Mezawa, Tetsuya; Mochizuki, Akihito; Sasamoto, Hiroshi
JAEA-Data/Code 2017-012, 60 Pages, 2017/10
Development of technologies to investigate properties of deep geological environment and model development of geological environment have been pursued in "Geoscientific Research" in the Horonobe Underground Research Laboratory (Horonobe URL) project. A geochemical model which is a part of geological environment model requires the data of groundwater chemistry around the Horonobe URL for the development. This report summarizes the data obtained for 3 years from the fiscal year 2014 to 2016, especially for the results for measurement of physico-chemical parameters and analysis of groundwater chemistry, in the Horonobe URL project.
Mezawa, Tetsuya; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi
JAEA-Data/Code 2017-010, 63 Pages, 2017/06
Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Geochemical parameters of groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater has been continuously monitored by the monitoring system which was developed in the Horonobe URL Project. This report presents the data of groundwater pressure which have been obtained by the monitoring system installed at the 140 m and 350 m gallery. The data obtained until March 31, 2016 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.
Sato, Toshinori; Sasamoto, Hiroshi; Ishii, Eiichi; Matsuoka, Toshiyuki; Hayano, Akira; Miyakawa, Kazuya; Fujita, Tomoo*; Tanai, Kenji; Nakayama, Masashi; Takeda, Masaki; et al.
JAEA-Research 2016-025, 313 Pages, 2017/03
The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formations at Horonobe, northern Hokkaido. This report summarizes the results of the Phase II investigations carried out from April 2005 to June 2014 to a depth of 350m. Integration of work from different disciplines into a "geosynthesis" ensures that the Phase II goals have been successfully achieved and identifies key issues that need to made to be addressed in the Phase II investigations Efforts are made to summarize as many lessons learnt from the Phase II investigations and other technical achievements as possible to form a "knowledge base" that will reinforce the technical basis for both implementation and the formulation of safety regulations.
Sasamoto, Hiroshi; Isogai, Takeshi*; Kikuchi, Hirohito*; Sato, Hisao*; Svensson, D.*
Clay Minerals, 52(1), p.127 - 141, 2017/03
Compacted bentonite has been considered as a candidate of engineering barrier material in many countries for the safe disposal of high-level radioactive waste. SKB set up an in situ experiment (named ABM project) to compare the stability of different bentonites under the conditions exposed to an iron source and elevated temperature (up to 130C as maximum) at the sp Hard Rock Laboratory, Sweden. Results for the Japanese bentonite (Kunigel V1) are summarized in the present paper. Mineralogical investigation using X-ray diffraction (XRD) and X-ray spectroscopy (SEM-EDX) suggested that no indication of smectite transformation or newly formed clay phases were observed. However, a distinct change of exchangeable cations of smectite was indicated (i.e., from Na type to Fe type) in the bentonite at the vicinity of the steel heater. Physical investigation by measurements of hydraulic conductivity and swelling property suggested that no significant change occur in the bentonite even at the vicinity of the steel heater. Such results might be considered due to the limited portion affected by the iron-bentonite interactions and partially occurred ion exchange reactions. Chemical investigation based on the measurements of methylane blue (MB), cation exchange capacity (CEC) and exchangeable cations showed that the lateral distribution for these parameters were basically constant without the significant gradient.
Sasaki, Takayuki*; Kokami, Takayuki*; Kobayashi, Taishi*; Kirishima, Akira*; Murakami, Hiroaki; Amano, Yuki; Mizuno, Takashi; Iwatsuki, Teruki; Sasamoto, Hiroshi; Miyakawa, Kazuya
Journal of Nuclear Science and Technology, 54(3), p.373 - 381, 2017/03
Trace amounts of natural thorium and uranium in deep groundwater were investigated at two underground research laboratories situated at Horonobe and Mizunami, Japan. The groundwater was sampled from underground boreholes, and the colloid contribution was checked by in situ two size-fractionated ultrafiltration systems. A decrease in the concentration after in situ filtration suggested the presence of natural colloids and suspended matter that were carriers of a portion of the elements. The result of the Th and U concentrations in groundwater after 10 kDa filtration was analyzed thermodynamically using existing hydrogeological and geochemical data such as the mineral components in the groundwater at a given pH, ionic strength, concentration of co-existing ions, redox potential, and solid phase assumed. A crystalline solid phase made the solubility very low compared with that of the amorphous phase, and the solubility agreed well with the concentrations measured.
Murakami, Takuma; Sasamoto, Hiroshi; Mizuno, Takashi
Chikyu Kagaku, 50(4), p.299 - 317, 2016/12
Development of techniques for investigating the long-term migration of elements in deep underground is important with respect to safety assessment for the geological disposal of high-level radioactive waste. As one study of the migration of elements in deep underground, the distribution of REE, Th and U in sedimentary rock of Horonobe area in Hokkaido was investigated, and discussed whether the difference of hydrogeological structure and lithofacies influences on the distributions. As the results, it was considered that REE and Th were mainly retained in minerals originating from terrigenous clastic and secondary mineral occurred in early diagenesis, and their distributions were relatively homogenous in both the Koetoi and Wakkanai formations. Uranium was indicated to be maintained in the sedimentary rock until now after depositing in deep-sea sediment. It was considered that the U deposition was occurred by adsorption on organic matter and reductive precipitation with decomposition of organic matter. In addition, it was confirmed that the distributions of these elements were not influenced by the difference of hydrogeological and lithofacies.
Hama, Katsuhiro; Sasao, Eiji; Iwatsuki, Teruki; Onoe, Hironori; Sato, Toshinori; Fujita, Tomoo; Sasamoto, Hiroshi; Matsuoka, Toshiyuki; Takeda, Masaki; Aoyagi, Kazuhei; et al.
JAEA-Review 2016-014, 274 Pages, 2016/08
We synthesized the research results from the Mizunami/Horonobe Underground Research Laboratories (URLs) and geo-stability projects in the second midterm research phase. This report can be used as a technical basis for the Nuclear Waste Management Organization of Japan/Regulator at each decision point from siting to beginning of disposal (Principal Investigation to Detailed Investigation Phase).
Mezawa, Tetsuya; Miyakawa, Kazuya; Sasamoto, Hiroshi; Soga, Koichi*
JAEA-Technology 2016-003, 25 Pages, 2016/05
Development of the monitoring technique for hydro-geochemical conditions of groundwater in low permeable sedimentary rocks with high content of dissolved gases in the underground facility is one of key issues in the Underground Research Laboratory (URL) project in order to obtain the reliable geochemical data. Development of the monitoring system for the groundwater geochemistry was conducted previously at the 140m gallery in the Horonobe URL. Thereafter, improvement and development of the monitoring system have been performed at the 350m gallery as the course of development technology to monitor the hydro-geochemical conditions during the URL construction. In this report, the results including the improvement and development of the monitoring system for the groundwater geochemistry at the 350m gallery and the several examples of data acquisition are presented.