Generic Natural Systems Evaluation - Thermodynamic Database Development and Data Management

Wolery, T W ; Sutton, M

Lawrence Livermore National Laboratory

关键词: Alloys;    54 Environmental Sciences;    Wipp;    Solubility;    Saturation;   

DOI  :  10.2172/1035958
RP-ID  :  LLNL-TR-500113
RP-ID  :  W-7405-ENG-48
RP-ID  :  1035958

美国|英语

来源: UNT Digital Library

【 摘 要 】

Thermodynamic data are essential for understanding and evaluating geochemical processes, as by speciation-solubility calculations, reaction-path modeling, or reactive transport simulation. These data are required to evaluate both equilibrium states and the kinetic approach to such states (via the affinity term or its equivalent in commonly used rate laws). These types of calculations and the data needed to carry them out are a central feature of geochemistry in many applications, including water-rock interactions in natural systems at low and high temperatures. Such calculations are also made in engineering studies, for example studies of interactions involving man-made materials such as metal alloys and concrete. They are used in a fairly broad spectrum of repository studies where interactions take place among water, rock, and man-made materials (e.g., usage on YMP and WIPP). Waste form degradation, engineered barrier system performance, and near-field and far-field transport typically incorporate some level of thermodynamic modeling, requiring the relevant supporting data. Typical applications of thermodynamic modeling involve calculations of aqueous speciation (which is of great importance in the case of most radionuclides), solubilities of minerals and related solids, solubilities of gases, and stability relations among the various possible phases that might be present in a chemical system at a given temperature and pressure. If a phase can have a variable chemical composition, then a common calculational task is to determine that composition. Thermodynamic modeling also encompasses ion exchange and surface complexation processes. Any and all of these processes may be important in a geochemical process or reactive transport calculation. Such calculations are generally carried out using computer codes. For geochemical modeling calculations, codes such as EQ3/6 and PHREEQC, are commonly used. These codes typically provide 'full service' geochemistry, meaning that they use a large body of thermodynamic data, generally from a supporting database file, to sort out the various important reactions from a wide spectrum of possibilities, given specified inputs. Usually codes of this kind are used to construct models of initial aqueous solutions that represent initial conditions for some process, although sometimes these calculations also represent a desired end point. Such a calculation might be used to determine the major chemical species of a dissolved component, the solubility of a mineral or mineral-like solid, or to quantify deviation from equilibrium in the form of saturation indices. Reactive transport codes such as TOUGHREACT and NUFT generally require the user to determine which chemical species and reactions are important, and to provide the requisite set of information including thermodynamic data in an input file. Usually this information is abstracted from the output of a geochemical modeling code and its supporting thermodynamic data file. The Yucca Mountain Project (YMP) developed two qualified thermodynamic databases to model geochemical processes, including ones involving repository components such as spent fuel. The first of the two (BSC, 2007a) was for systems containing dilute aqueous solutions only, the other (BSC, 2007b) for systems involving concentrated aqueous solutions and incorporating a model for such based on Pitzer's (1991) equations. A 25 C-only database with similarities to the latter was also developed for the Waste Isolation Pilot Plant (WIPP, cf. Xiong, 2005). The NAGRA/PSI database (Hummel et al., 2002) was developed to support repository studies in Europe. The YMP databases are often used in non-repository studies, including studies of geothermal systems (e.g., Wolery and Carroll, 2010) and CO2 sequestration (e.g., Aines et al., 2011).