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JAEA Reports

Models of Cement-Water Interaction of Associated Thermodynamic Datand North America

D.Savag*; K.Lemke*; Sasamoto, Hiroshi; Shibata, Masahiro; Randolp*; 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

QA issues for site hydrochemical data used for groundwater evolution models

Sasamoto, Hiroshi; Yui, Mikazu; D.Savag*; 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.

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