EQ6, a computer program for reaction path modeling of aqueous geochemical systems: Theoretical manual, user`s guide, and related documentation (Version 7.0); Part 4

EQ6 is a FORTRAN computer program in the EQ3/6 software package (Wolery, 1979). It calculates reaction paths (chemical evolution) in reacting water-rock and water-rock-waste systems. Speciation in aqueous solution is an integral part of these calculations. EQ6 computes models of titration processes (including fluid mixing), irreversible reaction in closed systems, irreversible reaction in some simple kinds of open systems, and heating or cooling processes, as well as solve ``single-point`` thermodynamic equilibrium problems. A reaction path calculation normally involves a sequence of thermodynamic equilibrium calculations. Chemical evolution is driven by a set of irreversible reactions (i.e., reactions out of equilibrium) and/or changes in temperature and/or pressure. These irreversible reactions usually represent the dissolution or precipitation of minerals or other solids. The code computes the appearance and disappearance of phases in solubility equilibrium with the water. It finds the identities of these phases automatically. The user may specify which potential phases are allowed to form and which are not. There is an option to fix the fugacities of specified gas species, simulating contact with a large external reservoir. Rate laws for irreversible reactions may be either relative rates or actual rates. If any actual rates are used, the calculation has a time frame. Several forms for actual rate laws are programmed into the code. EQ6 is presently able to model both mineral dissolution and growth kinetics

Computer simulation of temperature-dependent equilibrium precipitation

The EQ3/EQ6 software package contains two computer codes (EQ3 and EQ6) and data files which form a useful tool in modeling precipitation from geothermal fluids caused by heating or cooling. The data files contain information on 140 aqueous species and nearly 150 minerals, and permit calculations over the temperature interval 0 to 350/sup 0/C. Assumption of homogeneous thermodynamic equilibrium in aqueous solution permits calculation of the driving forces for precipitation as measured by the affinity (log Q/K) for each such reaction. Further assumption of precipitation and heterogeneous equilibrium for any mineral whose affinity would otherwise exceed a value of zero permits determination of the identity of the precipitates, their masses and volumes, and the temperature ranges in which they form. The EQ3/EQ6 capability was used to determine the effects of temperature increase on formation of precipitates form Salton Sea water

Post Emplacement Environment of Waste Packages

Experiments have been conducted as part of the Nevada Nuclear Waste Storage Investigations Project to determine the changes in water chemistry due to reaction of the Topopah Spring tuff with natural groundwater at temperatures up to 150{sup 0}C. The reaction extent has been investigated as a function of rock-to-water ratio, temperature, reaction time, physical state of the samples, and geographic location of the samples within the tuff unit. Results of these experiments will be used to provide information on the water chemistry to be expected if a high-level waste repository were to be constructed in the Topopah Spring tuff. 6 references, 5 figures, 1 table

EQPT, a data file preprocessor for the EQ3/6 software package: User`s guide and related documentation (Version 7.0); Part 2

EQPT is a data file preprocessor for the EQ3/6 software package. EQ3/6 currently contains five primary data files, called datao files. These files comprise alternative data sets. These data files contain both standard state and activity coefficient-related data. Three (com, sup, and nea) support the use of the Davies or B-dot equations for the activity coefficients; the other two (hmw and pit) support the use of Pitzer`s (1973, 1975) equations. The temperature range of the thermodynamic data on these data files varies from 25{degrees}C only to 0-300{degrees}C. The principal modeling codes in EQ3/6, EQ3NR and EQ6, do not read a data0 file, however. Instead, these codes read an unformatted equivalent called a data1 file. EQPT writes a datal file, using the corresponding data0 file as input. In processing a data0 file, EQPT checks the data for common errors, such as unbalanced reactions. It also conducts two kinds of data transformation. Interpolating polynomials are fit to data which are input on temperature adds. The coefficients of these polynomials are then written on the datal file in place of the original temperature grids. A second transformation pertains only to data files tied to Pitzer`s equations. The commonly reported observable Pitzer coefficient parameters are mapped into a set of primitive parameters by means of a set of conventional relations. These primitive form parameters are then written onto the datal file in place of their observable counterparts. Usage of the primitive form parameters makes it easier to evaluate Pitzer`s equations in EQ3NR and EQ6. EQPT and the other codes in the EQ3/6 package are written in FORTRAN 77 and have been developed to run under the UNIX operating system on computers ranging from workstations to supercomputers

Post emplacement environment of waste packages

Experiments have been conducted as part of the Nevada Nuclear Waste Storage Investigations Project to determine the changes in water chemistry due to reaction of the Topopah Spring tuff with natural groundwater at temperatures up to 150{sup 0}C. The reaction extent has been investigated as a function of rock-to-water ratio, temperature, reaction time, physical state of the samples, and geographic location of the samples within the tuff unit. Results of these experiments will be used to provide information on the water chemistry to be expected if a high-level waste repository were to be constructed in the Topopah Spring tuff. 6 references, 5 figures, 1 table

LLNL Yucca Mountain project - near-field environment characterization technical area: Letter report: EQ3/6 version 8: differences from version 7

EQ3/6 is a software package for geochemical modeling of aqueous systems, such as water/rock or waste/water rock. It is being developed for a variety of applications in geochemical studies for the Yucca Mountain Site Characterization Project. The software has been extensively rewritten for Version 8. The source code has been extensively modernized. The software is now written in Fortran 77 with the most common extensions that are part of the new Fortran 90 standard. The architecture of the software has been improved for better performance and to allow the incorporation of new functional capabilities in Version 8 and planned subsequent versions. In particular, the structure of the major data arrays has been significantly altered and extended. Three new major functional capabilities have been incorporated in Version 8. The first of these allows the treatment of redox disequilibrium in reaction-path modeling. This is a natural extension of the long-running capability of providing for such disequilibrium in static speciation-solubility calculations. Such a capability is important, for example, when dealing with systems containing organic species and certain dissolved gas species. The user defines (and sets the controls for) the components in disequilibrium. Such corrections can now be made if the requisite data are present on a supporting data file. At present, this capability is supported only by the SHV data file, which is based on SUPCRT92. Equilibrium constants and other thermodynamic quantities are correct1961ed for pressures which lie off a standard curve, which is defined on the supporting data file and ordinarily corresponds to 1.013 bar up to IOOC, and the steam/liquid water equilibrium pressure up to 300C. The third new major capability is generic ion exchange option previously developed in prototype in a branch Version 7 level version of EQ3/6 by Brian Viani, Bill Bourcier, and Carol Bruton. This option has been modified to fit into the Version 8 data structure, which allows avoidance of some problems that occurred with the prototype. This capability allows the user to define exchange phases with multiple sites, specifying the exchange reactions and relevant thermodynamic data. Some minor improvements have also been made. The major option switch arrays for EQ3NR and EQ6 (iopt, iopr, iodb) have been made identical for both codes (though some elements may only pertain to one code or the other). EQ3NR now accepts alkalinity in units of mg/L equivalent CaCO3, in accord with the usual method of presenting data for groundwater chemistry. A previous treatment of alkalinity had been removed from the Version 7 series. Supporting data files may now utilize temperature-pressure grids with arbitrary numbers of temperature ranges and temperature points per range, instead of the old EQ3/6 standard of two temperature ranges with four and five points (one point being common to both temperature ranges). Version 8 of EQ3/6 also includes utility codes to convert EQ3NR and EQ6 input files from version levels 7 and 7.2 level to version level 8

Chemical modeling of irreversible reactions in nuclear waste-water-rock systems

Chemical models of aqueous geochemical systems are usually built on the concept of thermodynamic equilibrium. Though many elementary reactions in a geochemical system may be close to equilibrium, others may not be. Chemical models of aqueous fluids should take into account that many aqueous redox reactions are among the latter. The behavior of redox reactions may critically affect migration of certain radionuclides, especially the actinides. In addition, the progress of reaction in geochemical systems requires thermodynamic driving forces associated with elementary reactions not at equilibrium, which are termed irreversible reactions. Both static chemical models of fluids and dynamic models of reacting systems have been applied to a wide spectrum of problems in water-rock interactions. Potential applications in nuclear waste disposal range from problems in geochemical aspects of site evaluation to those of waste-water-rock interactions. However, much further work in the laboratory and the field will be required to develop and verify such applications of chemical modeling

EQ3/6, a software package for geochemical modeling of aqueous systems: Package overview and installation guide (Version 7.0)

EQ3/6 is a software package for geochemical modeling of aqueous systems. This report describes version 7.0. The major components of the package include: EQ3NR, a speciation-solubility code; EQ6, a reaction path code which models water/rock interaction or fluid mixing in either a pure reaction progress mode or a time mode; EQPT, a data file preprocessor, EQLIB, a supporting software library; and five supporting thermodynamic data files. The software deals with the concepts of thermodynamic equilibrium, thermodynamic disequilibrium, and reaction kinetics. The five supporting data files contain both standard state and activity coefficient-related data. Three support the use of the Davies or B-dot equations for the activity coefficients; the other two support the use of Pitzer`s equations. The temperature range of the thermodynamic data on the data files varies from 25{degree}C only to 0--300{degree}C. EQPT takes a formatted data file (a data0 file) and writes an unformatted near-equivalent called a datal file, which is actually the form read by EQ3NR and EQ6. EQ3NR is useful for analyzing groundwater chemistry data, calculating solubility limits, and determining whether certain reactions are in states of partial equilibrium or disequilibrium. It is also required to initialize an EQ6 calculation. EQ6 models the consequences of reacting an aqueous solution with a set of reactants which react irreversibly. It can also model fluid mixing and the consequences of changes in temperature. This code operates both in a pure reaction progress frame and in a time frame

EQPT, a data file preprocessor for the EQ3/6 software package: User`s guide and related documentation (Version 7.0); Part 2

EQPT is a data file preprocessor for the EQ3/6 software package. EQ3/6 currently contains five primary data files, called datao files. These files comprise alternative data sets. These data files contain both standard state and activity coefficient-related data. Three (com, sup, and nea) support the use of the Davies or B-dot equations for the activity coefficients; the other two (hmw and pit) support the use of Pitzer`s (1973, 1975) equations. The temperature range of the thermodynamic data on these data files varies from 25{degrees}C only to 0-300{degrees}C. The principal modeling codes in EQ3/6, EQ3NR and EQ6, do not read a data0 file, however. Instead, these codes read an unformatted equivalent called a data1 file. EQPT writes a datal file, using the corresponding data0 file as input. In processing a data0 file, EQPT checks the data for common errors, such as unbalanced reactions. It also conducts two kinds of data transformation. Interpolating polynomials are fit to data which are input on temperature adds. The coefficients of these polynomials are then written on the datal file in place of the original temperature grids. A second transformation pertains only to data files tied to Pitzer`s equations. The commonly reported observable Pitzer coefficient parameters are mapped into a set of primitive parameters by means of a set of conventional relations. These primitive form parameters are then written onto the datal file in place of their observable counterparts. Usage of the primitive form parameters makes it easier to evaluate Pitzer`s equations in EQ3NR and EQ6. EQPT and the other codes in the EQ3/6 package are written in FORTRAN 77 and have been developed to run under the UNIX operating system on computers ranging from workstations to supercomputers

Extension of the EQ3/6 computer codes to geochemical modeling of brines

Recent modifications to the EQ3/6 geochemical modeling software package provide for the use of Pitzer's equations to calculate the activity coefficients of aqueous species and the activity of water. These changes extend the range of solute concentrations over which the codes can be used to dependably calculate equilibria in geochemical systems, and permit the inclusion of ion pairs, complexes, and undissociated acids and bases as explicit component species in the Pitzer model. Comparisons of calculations made by the EQ3NR and EQ6 compuer codes with experimental data confirm that the modifications not only allow the codes to accurately evaluate activity coefficients in concentrated solutions, but also permit prediction of solubility limits of evaporite minerals in brines at 25/sup 0/C and elevated temperatures. Calculations for a few salts can be made at temperatures up to approx. 300/sup 0/C, but the temperature range for most electrolytes is constrained by the availability of requisite data to values less than or equal to 100/sup 0/C. The implementation of Pitzer's equations in EQ3/6 allows application of these codes to problems involving calculation of geochemical equilibria in brines; such as evaluation of the chemical environment which might be anticipated for nuclear waste canisters located in a salt repository. 26 references, 3 figures, 1 table