Iwatsuki, Teruki; Arthur, R. C,*
Thermodynamics, Solubility and Environmental Issues, p.153 - 168, 2007/04
Maximum uranium concentrations in groundwaters associated with a uranium ore deposit in Japan appear to be controlled by the solubility of the amorphous hydrous oxide, UO(am). This conclusion is supported by calculated saturation indices for this mineral using geochemical data characterizing the deposit and its surroundings. The conclusion that UO(am) appears to be solubility controlling in a natural system that has evolved over long periods of time supports the assumption adopted in many international studies that the solubility of this phase would limit the aqueous concentrations of U released from a deep geologic repository for nuclear wastes over similar time scales. Natural systems can thus provide a useful framework for testing assumptions and models used in repository safety assessments.
Sasao, Eiji; Ota, Kunio; Iwatsuki, Teruki; Niizato, Tadafumi; Arthur, R. C,*; Stenhouse, M. J.*; Zhou, W.*; Metcalfe, R.*; Takase, Hiroyasu; MacKenzie, A. B.*
Geochemistry; Exploration, Environment, Analysis, 6(1), p.5 - 12, 2006/02
The present natural analogue study of the Tono uranium deposit (Tono Natural Analogue Project) was started in 2001 with the main aim of studying a worst case scenario for safety assessment. The project has involved characterising the geology, hydrogeology, geochemistry and microbiology of the deposit and obtaining quantitative information about specific times in the past, as a means for developing, and building confidence in, conceptual and numerical models. Some recent results from site investigations, such as depositional age of the host sedimentary sequence and fault activity, are presented in this paper and in other papers in the series.
Oda, Chie; Sasaki, Ryoichi; Honda, Akira; Savage, D.*; Arthur, R. C,*
JNC TN8400 2005-020, 39 Pages, 2005/09
The multiple scenarios of bentonite alteration were ideveloped based on the possible mineralogical changes derived from knowledge of both experiments and observation of natural systems. It was focused that the mineral reaction involving hyperalkaline fluid thermodynamically depends on the variable chemical condition in bentonite buffer and that kinetics is important as well as thermodynamic stability in controlling their occurrence, i.e., the kinetic controls operate to remain metastable minerals over the long term. The mineralogical consequences of the interaction between clays and alkaline fluid are summarized as follows. / -Clay and gel illite / -Clay and gel metastable zeolite stable zeolite and feldspar / -Clay and gel stable zeolite and feldspar The typical minerals for each category (illite group, metastable zeolite group and stable zeolite and feldspar group) were selected. The scenarios give the range of potential secondary minerals occurring in chemical schemes of the bentonite alteration by cement pore fluids, and thus reasonable assumptions on the simulation of the chemical and mineralogical evolutions of geological disposal system for TRU waste.
Arthur, R. C,*; Sasamoto, Hiroshi; Oda, Chie; Honda, Akira; Shibata, Masahiro; Yoshida, Yasushi*; Yui, Mikazu
JNC TN8400 2005-010, 234 Pages, 2005/07
This report describes three thermodynamic databases for minerals, gases, aqueous species and reactions of relevance to bentonite and cement barriers in geologic repositories for transuranic (TRU) and other nuclear wastes. The databases support calculations using the SUPCRT, PHREEQC and GWB geochemical codes, and are referred to as SPRONS.TRU (SUPCRT), JNC-TDB.TRU (PHREEQC) and THERMO_ JNCTRU (GWB). The reliability of these databases should be considered in the context of basic limitations in current conceptual models of clay-bearing, high-pH systems. Minerals that are important in such systems tend to be complex, possibly metastable solid solutions having highly variable compositions that have not been well characterized experimentally or thermodynamically. There is also considerable uncertainty regarding important aqueous species in such systems due to the paucity of relevant experimental data presently available. With these limitations in mind, the databases developed in this study are considered to be reliable insofar as they include data for minerals that are known to be important or representative of hyperalkaline, argillaceous systems, and because the data are in general demonstrably accurate in cases where comparisons can be made between calculated values and their experimental counterparts. The databases may not meet the ideal standard of an internally consistent database because more weight has been given in this study to the accuracy and completeness of the data than to their internal consistency. An approach recommended for future improvements and revisions of the databases described in this report includes the development of a consistent set of empirical methods permitting routine estimation of thermodynamic properties in cases where reliable experimental data are lacking, combined with uncertainty analyses to assess the importance of conceptual and parameter uncertainties on models of the long-term behavior of bentonite and cementitious barriers.
Sasamoto, Hiroshi; Yui, Mikazu; Arthur, R. C,*
Proceedings of 2nd International Meeting on Clays in Natural and Engineered barriers for Radioactive Waste Confinement (TOURS 2005) (CD-ROM), p.259 - 260, 2005/03
Saline type groundwaters with oil, gas and coal fields are identified in the JNC's extensive database of groundwater samples from throughout Japan. Groundwater data in the Mobara area (a marine based argillaceous rock) located in the well-known
Yui, Mikazu; Sasamoto, Hiroshi; Arthur, R. C,*
Geochemical Journal, 38(1), p.33 - 42, 2004/00
Arthur, R. C,*
JNC TJ7400 2003-007, 52 Pages, 2003/03
In this research, the following three items have been considered for the purpose of construction of the geochemical model which can express the chemical reaction in groundwater correctly. Evaluation of the quality of the previous analytical data in the Tono region, Grasp of the chemical character of groundwaters, Consideration about the influence between Eh, pH and CO2(g) parameter, and which the change has.
Arthur, R. C,*; Savage, D.*; Sasamoto, Hiroshi; Shibata, Masahiro; Yui, Mikazu
JNC TN8400 2000-005, 61 Pages, 2000/01
Kinetic data, including rate constants, reaction orders and activation energies, are compiled for 34 hydrolysis reactions involving feldspars, sheet silicates, zeolites, oxides, pyroxenes and amphiboles, and for similar reactions involving calcite and pyrite. The data are compatible with a rate law consistent with surface reaction control and transition-state theoly, which is incorporated in the geochemieal software package EQ3/6 and GWB. Kinetic data for the reactions noted above are strictly compatible with the transition-state rate law only under far-from-equilibrium conditions. It is possiblethat the data are conceptually consistent with this rate law under both far-from-equilibrium and near-to-equilibrium conditions, but this should be confirmed whenever possible through analysis of original experimental results, Due to limitations in the availability of kinetic data for mineral-water reactions, and in order to simplify evaluations of geochemical models of groundwater evolution, it is convenient to assume local-equilibrium in such models whenever possible. To assess whether this assumption is reasonable, a modeling approach accounting for coupled fluid flow and water-rock interaction is described that can be used to estimate spatial and temporal scale of local equiliblium. The approach is demonstrated for conditions involving groundwater flow in fractures at JNC's Kamaishi in-situ tests site, and is also used to estimate the travel time necessary for oxidizing surface waters to migrate to the level of a HLW repository in crystalline rock. The question of whether local equilibrium is a reasonable assumption must be addressed using an appropriate modeling approach. To be appropriate for conditions at the Kamaishi site using the modeling approach noted above, the fracture fill must closely approximate a porous medium, groundwater flow must be purely advective and diffusion of solutes across the fracture-host rock boundary must not occur. Moreover, the ...
Savage, D.*; Lemke, K.*; Sasamoto, Hiroshi; Shibata, Masahiro; Arthur, R. C,*; Yui, Mikazu
JNC TN8400 2000-004, 30 Pages, 2000/01
Modeling approaches that have been proposed for cement-water system are reviewed in this report, and relevant supporting thsrmodynamic data are compiled. The thermodynamic data include standard molal thermodynamic properties of minerals and related compounds comprising cements, and equilibrium constants for associated hydrolysis reactions. Similar data for minerals that are stable in hyperalkaline geologic environments (e.g., zeolites) are also included because these minerals could be formed as hyperalkaline fluids emanating from cementitious matelials in a repository for radioactive wastes interact with the surrounding host rock. Standard molal properties (i.e., standard molal Gibbs free energies and enthalpies of formation and standard molal entropies), and/or equilibrium constants for associated hydrolysis reactions, are included for. (1)cement minerals and related compounds (Reardon, 1992; Glasser et al., 1999) (2)calcium-silicate hydrate minerals (Sarkar et al., 1982), and (3)zeolites (calorimetric and estimated values from various sources) All these data are accepted at face value, and it is therefore cautioned that the data, considered as a whole, may not be internally consistent. It is also important to note that the accuracy of these data have not been evaluated in the present study. Several models appropriate for cement-water systems have been proposed in recent years. Most are similar in the sense that they represent empirical fits to laboratory data for the CSH gel-water system, and therefore not thermodynamically defensible. An alternative modeling approach based on thermodynamic principles of solid-solution behavior appropriate for CSH gel has recently been proposed, however. It is reviewed in the present study, and evaluated in relation to experimental results obtained by JNC on cement-water interactions. The solid-solution model is based upon a thermodynamically- and structually-justifiable description of CSH gel in terms of a non-ideal ...
Savage, D.*; Arthur, R. C,*; Sasamoto, Hiroshi; Shibata, Masahiro; Yui, Mikazu
JNC TN8400 2000-003, 56 Pages, 2000/01
Geochemical as well as socio-economic issues associated with the selection of potential sites to host a high-level nuclear waste repository have received considerable attention in repository programs in Europe (Belgium, Finland, France, Germany, Spain, Sweden, Switzerland and the U.K.) and North America (Canada and the United States), The objective of the present study is to summarize this international experience with particular emphasis on geochemical properties that factor into the adopted site-selection strategies. Results indicate that the geochemical properties of a site play a subordinate role, at best, to other geotechnical properties in the international site-selection approaches. In countries where geochemical properties are acknowledged in the site-selection approach, requirements are stated qualitatively and tend to focus on associated impacts on the stability of the engineered barrier system and on radionuclide transport. Site geochemical properties that are likely to control the lomg-term stability of geochemical conditions and radionuclide migration behavior are unspecified, however. This non-prescriptive approach may be reasonable for purposes of screeing among potential sites, but a better understanding of site properties that are most important in controlling the long-term geochemical evolution of the site over a range of possible scenarios would enable the potential sites to be ranked in terms of their suitability to host a repository.
Oda, Chie; Arthur, R. C,*; Sasamoto, Hiroshi; Shibata, Masahiro; Yui, Mikazu; Neyama, Atsushi*
JNC TN8400 99-079, 287 Pages, 1999/09
Two thermodynamic databases for geochemical calculations supporting research and development on geological disposal concepts for high level radioactive waste are described in this report. One, SPRONS.JNC, is compatible with thermodynamic relations comprising the SUPCRT model and software, which permits calculation of the standard molal and partial molal thermodynamic properties of minerals, gases, aqueous species and reactions from 1 to 5000 bars and 0 to 1000C. This database includes standard molal Gibbs free energies and enthalpies of formation, standard molal entropies and volumes, and Maier-Kelly heat capacity coefficients at the reference pressure (1 bar) and temperature (25C) for 195 minerals and 16 gases. It also includes standard partial molal Gibbs free energies and enthalpies of formation, standard partial molal entropies, and Helgeson, Kirkham and Flowers (HKF) equation-of-state coefficients at the reference pressure and temperature for 1147 inorganic and organic aqueous ions and complexes. SPRONS.JNC extends similar databases described elsewhere by incorporating new and revised data published in the peer-reviewed literature since 1991. The other database, PHREEQE.JNC, is compatible with the PHREEQE series of geochemical modeling codes. It includes equilibrium constants at 25C and 1 bar for mineral-dissolution, gas-solubility, aqueous-association and oxidation-reduction reactions. Reaction enthalpies, or coefficients in an empirical log K(T) function, are also included in this database, which permits calculation of equilibrium constants between 0 and 100C at 1 bar. All equilibrium constants, reaction enthalpies, and logK(T) coefficients in PHREEQE.JNC are calculated usig SUPCRT and SPRONS.JNC, which ensures that these two databases are mutually consistent. They are also internally consistent insofar as all the data are compatible with basic thermodynamic definitions and functional relations in the SUPCRT ...
Sasamoto, Hiroshi; Yui, Mikazu; Arthur, R. C,*
JNC TN8400 99-033, 153 Pages, 1999/07
The results of hydrochemical investigations of groundwaters in the Kurihashi granodiorite at JNC's Kamaishi in-situ tests site indicate that these solutions are: (1)meteoric in origin, (2)chemically reducing (at depths greater than a few hundreds meters), (3)relatively young [residence times in the Kurihashi granodiorite generally less than about 40 years, but groundwaters older than several thousand years BP (before present) are also indicated by preliminary carbon-14 dating of samples obtained from the KH-1 borehole], (4)Ca-HCO type solutions near the surface, changing to Na-HCO type groundwaters with increasing depth. The evolution of groundwater compositions in the Kurihashi granodiorite is modeled assuming local equilibrium for selected mineral-fluid reactions, taking into account the rainwater origin of these solutions. Results suggest it is possible to interpret approximately the "real" groundwater chemistry (i.e., pH, Eh, total dissolved concentrations of Si, Na, Ca, K, AI, carbonate and sulfate) in the Kurihashi granodiorite if the following assumptions are adopted: (1)CO concentration in the gas phase contacting pore solutions in the overlying soil zone = 10 bar, (2)minerals in the rock zone that control the solubility of respective elements in the groundwater include; chalcedony (Si), albite (Na), kaolinite (Al), calcite (Ca and carbonate), microcline (K) and pyrite (Eh and sulfate). Discussions with international experts suggest a systematic approach utilizing reaction-path models of irreversible water-rock interactions in open systems may be needed to more realistically model groundwater evolution at the Kamaishi test site. Detailed information characterizing certain site properties (e.g., fracture mineralogy) may be required to adequately constrain such models, however.
Oda, Chie; Sasaki, Ryoichi; Arthur, R. C,*; Savage, D.*; Honda, Akira
no journal, ,
Bentonite materials are expected to be used as the main hydraulic barrier and cementitious materials are expected to be used for structure support in low level radioactive waste disposal systems. Interaction between bentonite and hyperalkaline fluids arising from cementitious materials has been recognized as a concern due to the close proximity of these materials in repository designs. The interaction could cause the alteration of mineralogy and associated hydraulic property of bentonite and have a deleterious influence on the function of bentonite as a hydraulic barrier, and may lead to adverse impact on the long-term safety of the repository. Many researches on such interaction have been performed to establish the bentonite alteration scheme, however, uncertainty in our understanding of the precise alteration scheme, especially mineral paragenetic sequences during the alteration, still remains. Therefore, it is important to take such uncertainty into account in estimating how the mineralogy and the hydraulic property of bentonite evolves subject to alteration by hyperalkaline fluids. In this work, multiple scenarios for mineralogical alteration of bentonite was investigated to limit the mineral paragenetic uncertainty and to identify appropriate assumption for numerical simulation of chemical and mineralogical evolution of bentonite under hyperalkaline conditions over the long-term.