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Journal Articles

Using natural systems evidence to test models of transformation of montmorillonite

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

 Times Cited Count:1 Percentile:0.02(Chemistry, Physical)

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.

Journal Articles

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

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

 Times Cited Count:5 Percentile:57.36(Chemistry, Physical)

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 140$$^{circ}$$C, 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 60$$^{circ}$$C to that for illite + quartz at higher temperatures. However, even over very long timescales ($$gg$$ 1 Ma), smectite does not transform to illite under thermodynamically-favourable conditions at temperatures less than 80$$^{circ}$$C.

Journal Articles

A Comparative study of the modelling of cement hydration and cement-rock laboratory experiments

Savage, D.*; Soler, J. M.*; Yamaguchi, Kohei; Walker, C.; Honda, Akira; Inagaki, Manabu; Watson, C.*; Wilson, J.*; Benbow, S.*; Gaus, I.*; et al.

Applied Geochemistry, 26(7), p.1138 - 1152, 2011/07

 Times Cited Count:16 Percentile:48.84(Geochemistry & Geophysics)

The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for rad wastes creates potential issues concerning chemical reactivity. From a long term safety perspective, it is desirable to be able model these interactions and changes quantitatively. As part of the LCS (Long-term Cement Studies) project programme, a modelling inter-comparison has been conducted, involving the modelling of two experiments describing cement hadration and cement-rock reaction, with teams representing the NDA (UK), Posiva (Finland), and JAEA. This modelling exercise showed that the dominant reaction pathways in the two experiments are fairly well understood and are consistent between the different modelling teams, although significant differences existed amongst the precise parameterisation. Future modelling exercises of this type should focus on a suitable natural or industrial analogue that might aid assessing mineral-fluid reactions at these longer timescales.

Journal Articles

Natural systems evidence for the alteration of clay under alkaline conditions; An Example from Searles Lake, California

Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*; Ono, Kaori*; Oda, Chie; Honda, Akira

Applied Clay Science, 47(1-2), p.72 - 81, 2010/01

 Times Cited Count:28 Percentile:68.95(Chemistry, Physical)

Mudstones containing smectite have been altered under mildly alkaline conditions (9 $$<$$ pH $$<$$ 10) at Searles Lake, California over a 3 million-year time period. This natural alteration has been simulated incorporating time-dependent boundary conditions of sedimentation and fluid composition, a Pitzer model for activities of aqueous species, and a coupled hydrogeological model for time-dependent flow in the sediment layers. Kinetic dissolution of detrital smectite under alkaline conditions was described using one of two models based on departure from thermodynamic equilibrium or by an empirical rate dependent upon aqueous Si concentrations. The zonal pattern of smectite dissolution observed at Searles Lake was reproduced reasonably well by the "Cama-TST" model of montmorillonite dissolution. This assessment provides a test of the accuracy and reliability of published data in the application of models of smectite dissolution in the long-term.

JAEA Reports

Multiple Scenarios of Bentonite Alteration

Oda, Chie; Sasaki, Ryoichi; Honda, Akira; Savage, D.*; Arthur, R. C,*

JNC TN8400 2005-020, 39 Pages, 2005/09

JNC-TN8400-2005-020.pdf:3.16MB

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 $$rightarrow$$ illite / -Clay and gel $$rightarrow$$ metastable zeolite $$rightarrow$$ stable zeolite and feldspar / -Clay and gel $$rightarrow$$ 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.

Journal Articles

An Analysis of the interaction between bentonite and hyperalkaline fluids with regard to mineral paragenetic uncertainty

Oda, Chie; Sasaki, Ryoichi; Takase, Hiroyasu*; Savage, D.*; Honda, Akira

Proceedings of International Workshop on Waste Management in Sapporo, p.163 - 165, 2005/08

The uncertainty in our understanding of the precise mineral paragenetic sequences of the interaction of bentonite with hyperalkaline fluids in the long-term still remains. In order to reflect this uncertainty, multiple scenarios of bentonite alteration were investigated based on the possible mineralogical changes derived from knowledge of both experiments and observation of natural systems.

Journal Articles

An Analysis of Bentonite-Cement Interaction and Evolution of Pore Water Chemistry

Oda, Chie; Honda, Akira; Sasaki, Ryoichi; Savage, D.*

Extended Abstractof International Workshop on Bentonite-Cement Interaction in Repository Environments, 7 Pages, 2004/04

The possible multiple scenarios of chemical-mineralogical evolution in Bentonite buffer were considered on the basis of the information of both experimental results and observations of natural systems. The range of variable chemical conditions according to each scenario was examined in terms of the potential for locally-attained chemical equilibrium and kinetics. These analyses have been intended to provide reasonable assumptions on simulations using chemistry-transport-hydrology coupling models that aims at estimating the possible evolution of hydraulic condition of bentonite in a TRU waste repository.

JAEA Reports

Sensitivity analysis to the geochemical parameters of the groundwater

Metcalfe, R.*; Savage, D.*; Bath, A. H.*; Walker, C.*

JNC TJ7400 2004-013, 148 Pages, 2004/03

JNC-TJ7400-2004-013.pdf:6.11MB

This report describes calculations of the solubilities of elements that are relevant to Performance Assessment in the groundwaters of the Tono area.

JAEA Reports

Models of Cement-Water Interaction and a Compilation of a Associated Thermodynamic Data

Savage, D.*; Lemke, K.*; Sasamoto, Hiroshi; Shibata, Masahiro; Arthur, R. C,*; Yui, Mikazu

JNC TN8400 2000-004, 30 Pages, 2000/01

JNC-TN8400-2000-004.pdf:1.26MB

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 ...

JAEA Reports

Geochemical Site-Selection Criteria for HLW Repositories in Europe and North America

Savage, D.*; Arthur, R. C,*; Sasamoto, Hiroshi; Shibata, Masahiro; Yui, Mikazu

JNC TN8400 2000-003, 56 Pages, 2000/01

JNC-TN8400-2000-003.pdf:1.96MB

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.

JAEA Reports

QA issues for site hydrochemical data used for groundwater evolution models

Sasamoto, Hiroshi; Yui, Mikazu; Savage, D.*; Bille, B.*

JNC TN8400 99-025, 32 Pages, 1999/06

JNC-TN8400-99-025.pdf:1.94MB

Groundwater data used for modelling site or repository evolution need to be assessed for their quality and whether they are "fit for purpose", prior to utilization. This report discuss factors and issues which impinge upon the quality of such data. It is recommended that geochemical modelleres : (1)are aware of how groundwater samples were collected, whether during drilling, during hydraulic testing, or thereafter, by in-situ measurement, pumped from boreholes, or by pressurised sampler ; (2)are aware of what procedures (if any) were used to "correct" samples for drill fluid contamination and what errors were associated with those methods ; (3)are aware of whether samples were subject to de-pressurisation during sampling, and whether geochemical modelling techniques were applied to correct the compositions of samples for that process ; (4)request different measures of redox activity (e.g., electrode measurements of Eh, concentrations of different redox-sensitive aqueous species) to be applied to key groundwater samples to investigate the extent of redox equilibrium ; (5)are aware of how groundwater samples were filtered and preserved for off-site analysis ; (6)ensure that adequate methods of groundwater filtration ($$<$$ 0.1$$mu$$m) and chemical analysis are applied to ensure accurate and reproducible analyses for dissolved aluminum at low levels of concentration (generally less than 0.2 mg/L) ; (7)are aware of elemental errors and detection limits in chemical analysis of groundwater samples and assess the quality of groundwater analyses via ion exchange balances and via a comparison of measured and calculated values for total dissolved solids contents. (8)ensure that detailed mineralogical analysis is carried out on rock samples from locations where key groundwater samples have been extracted.

Oral presentation

Alteration scenario for bentonite under hyperalkaline conditions with regard to mineral paragenetic uncertainty

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.

Oral presentation

Natural analogue in relation to alkaline alteration of clayey buffer material; An Example from the Searles Lake, California, 2; A Geochemical-transport modelling

Oda, Chie; Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*

no journal, , 

An natural clay alteration at Searles Lake, California has been investigated using reaction-transport modelling with the computer code employing time-dependent boundary conditions of sedimentation and fluid composition. The evidence in natural systems can demonstrate that alkaline alteration will be controlled by kinetic-geochemical reaction and transport coupling process, and that advective fluid flow and the salinity of the pore fluid eill be important factors.

Oral presentation

Groundwater patterns in a Playa Lake Basin, California; Analogue studies for geological disposal

Gallardo, A.*; Savage, D.*; Benbow, S.*; Takase, Hiroyasu*; Oda, Chie

no journal, , 

A numerical model was constructed to understand the groundwater flow dynamics and salinity distribution in the Searles Lake, California, a dry and alkaline playa lake, as a natural analogue for processes in a potential geological repository. The result shows that vertical flow would prevail at the center of the lake, and under this condition, salts would be dissolved from shallow evaporitic horizons being redistributed downwards and away from the lake surface. Concentrations up to 220 g/L would occur within an area approximately 6 by 4 km, extending to a depth of 200 m after 200,000 years. Although several uncertainties remain, the model is consistent with many observations, and provides a framework to address geochemical processes in the basin.

Oral presentation

Natural analogue in relation to alkaline alteration of clayey buffer material; An Example from the Searles Lake, California

Oda, Chie; Yamaguchi, Kohei; Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*

no journal, , 

Mudstones containing smectite have been altered under mildly alkaline conditions (9 $$<$$ pH $$<$$ 10) at Searles Lake. This natural alteration has been investigated using reaction-transport modelling. These data demonstrate that smectite alteration will be controlled by the kinetics of dissolution-precipitation reaction and the salinity of the pore fluid.

Oral presentation

Reactive transport modelling of iron-bentonite interface evolution

Wilson, J.*; Watson, C.*; Benbow, S.*; Savage, D.*; Sasamoto, Hiroshi

no journal, , 

Iron steel overpack will be surrounded by bentonite buffer as a engineering barrier system for the high-level radioactive waste disposal. It is concerned that iron-bentonite interactions result in the alteration of montmorillonite to non-swelling Fe-rich minerals. In the present study, reactive transport modeling of iron-bentonite interface evolution has been conducted to evaluate the long-term behavior of bentonite stability. A number of model cases were produced in order to assess which processes are likely to dominate at iron-bentonite interfaces.

Oral presentation

Using natural systems data to test models of transformation of montmorillonite

Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio

no journal, , 

Safety functions for the clay buffer in a repository for HLW are fulfilled if the presence of montmorillonite is maintained in the long-term. Its transformation to non-swelling minerals (e.g. illite) is addressed in most safety assessments by using semi-empirical kinetic models. However, this approach contrasts with all other near-field geochemical modelling activities that employ complex reaction-transport simulations. Here we investigate the consistency of these two approaches by modelling the montmorillonite to illite transformation in the marine sediment profile penetrated by the Ocean Drilling Program (ODP) Site 1174. Illitisation of smectite at Site 1174 using the semi-empirical approach has been modeled by previous studies, and shown to provide a reasonable match to the gradual change of illite content with depth. In comparison, the initial results of reaction-transport simulations showed rapid (conservative) conversion of montmorillonite to illite. The cause of this rapid conversion appears to be the transformation of amorphous silica to quartz over a similar timescale. Subsequent simulations have focused on alternative mechanisms for mineral growth that may explain the discrepancies between the semi-empirical and reaction-transport approaches.

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