Environment on the Surfaces of the Drip Shield and Waste Package Outer Barrier

This report provides supporting analysis of the conditions at which an aqueous solution can exist on the drip shield or waste package surfaces, including theoretical underpinning for the evolution of concentrated brines that could form by deliquescence or evaporation, and evaluation of the effects of acid-gas generation on brine composition. This analysis does not directly feed the total system performance assessment for the license application (TSPA-LA), but supports modeling and abstraction of the in-drift chemical environment (BSC 2004 [DIRS 169863]; BSC 2004 [DIRS 169860]). It also provides analyses that may support screening of features, events, and processes, and input for response to regulatory inquiries. This report emphasizes conditions of low relative humidity (RH) that, depending on temperature and chemical conditions, may be dry or may be associated with an aqueous phase containing concentrated electrolytes. Concentrated solutions at low RH may evolve by evaporative concentration of water that seeps into emplacement drifts, or by deliquescence of dust on the waste package or drip shield surfaces. The minimum RH for occurrence of aqueous conditions is calculated for various chemical systems based on current understanding of site geochemistry and equilibrium thermodynamics. The analysis makes use of known characteristics of Yucca Mountain waters and dust from existing tunnels, laboratory data, and relevant information from the technical literature and handbooks

EQ3/6 software maintenance and support summary

EQ3/6 is a software package for modeling chemical interactions in aqueous systems of geologic and engineering interest, such as water/rock, water/nuclear waste, and water/nuclear waste/rock. It is being used for a broad range of applications for the Yucca Mountain Site Characterization Project (YMSCP), including predictions of mineralogical changes in the altered zone, man-made materials investigations, and calculations of the long-term release of radionuclides from a variety of waste forms. Version 7.2a was the first qualified version of this software (certified on Aug. 17, 1994). Version 7.2b followed on Aug. 18, 1995 and is the most recent qualified version; it differs from version 7.2a only in that defects noted in the qualification report (Kishi, 7/12/94) were resolved. The present report describes the software maintenance and support activities that were carried out for the Version 7 line of the software in FY97. The most important of these activities is maintaining a system for the logging, documenting, and resolving software defects. This is required by the QARD (Supplement 1) in order for the software to remain certified. Other maintenance activities are necessary to retain functionality as computer hardware, operating systems, programming languages, and compilers change. In FY97, 12 software defects were logged and resolved, and two more were logged and awaiting resolution. These ranged in nature from the trivial to the serious. The corrected software will be released as version 7.2c in the first quarter of FY98. A version 8 line of totally rewritten code in modern Fortran, restructured to support new functionality, and with new capabilities for ion exchange modeling, pressure corrections, and redox disequilibrium, was completed to a baseline level in FY95. Subsequent activities required to complete qualification were not funded in FY96 and FY97. However, in FY97, each line of the software (version 7 and version 8) has been checked whenever a defect has been discovered in the other. A beta release of version 8.0 was made available to selected users in FY97. Qualification of version 8.0 may follow in FY98, depending on funding and direction. If this occurs, the certified software in the version 7 line will likely be retired and maintenance and support activities exclusively focused on the version 8 line

Letter report: status on code maintenance (EQ3/6)

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. Version 7.2a was the first version of this software to be certified for use in quality- affecting work (originally issued for use in non-quality-affecting work only on 12/28/93; certified on S/17/94). In the past year, the Version 7 line software has been maintained while the new Version 8 line has been developed. In this period, sixteen defect reports have been logged and resolved. Corrected software is being released as Version 7.2b. Defect reporting and resolution for the Version 7 line will continue until all released versions in this line are retired, perhaps six months to a year after Version 8.0 is released later this year. The Version 7 software is written in Fortran 77, technically speaking, but incorporates many aspects of older Fortran. The Version 8 software is written in a much more modern Fortran, technically somewhere between Fortran 77 and Fortran 90. Future code maintenance activities will include a more complete move to Fortran 90, as well as continued maintaining of defect reporting and resolution

EQ3/6 geochemical modeling task plan for Nevada Nuclear Waste Storage Investigations (NNWSI)

This task plan outlines work needed to upgrade the EQ3/6 geochemical code and expand the supporting data bases to allow the Nevada Nuclear Waste Storage Investigations (NNWSI) to model chemical processes important to the storage of nuclear waste in a tuff repository in the unsaturated zone. The plan covers the fiscal years 1984 to 1988. The scope of work includes the development of sub-models in the EQ3/6 code package for studying the effects of sorption, precipitation kinetics, redox disequilibrium, and radiolysis on radionuclide speciation and solubility. The work also includes a glass/water interactions model and a geochemical flow model which will allow us to study waste form leaching and reactions involving the waste package. A special emphasis is placed on verification of new capabilities as they are developed and code documentation to meet NRC requirements. Data base expansion includes the addition of elements and associated aqueous species and solid phases that are specific to nuclear waste (e.g., actinides and fission products) and the upgrading and documentation of the thermodynamic data for other species of interest

Generic Natural Systems Evaluation - Thermodynamic Database Development and Data Management

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)

The Standard Chemical-Thermodynamic Properties of Phosphorus and Some of its Key Compounds and Aqueous Species: An Evaluation of Differences between the Previous Recommendations of NBS/NIST and CODATA

The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate ions H{sub 3}PO{sub 4}{sup 0}(aq), H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), or PO{sub 4}{sup 3-}(aq). Many divalent, trivalent, and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation requires comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier; with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H{sub 2}PO{sub 4}{sup -}(aq) and HPO{sub 4}{sup 2-}(aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ {center_dot} mol{sup -1} per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H{sub 2}PO{sub 4}{sup -}(aq), HPO{sub 4}{sup 2-}(aq), and PO{sub 4}{sup 3-}(aq) ions at 298.15 K and p{sup o} = 1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S{sub m}{sup o}(H{sub 2}PO{sub 4}{sup -}, aq, 298.15 K) = 90.6 {+-} 1.5 J {center_dot} K{sup -1} mol{sup -1} was obtained