Technical Report NTB 91-17

A number of geochemical computer models are used within the Nagra programme to calculate speciation in aqueous solutions and the states of mineral-water equilibria. The thermochemical data bases accompanying these modelling programs do not contain identical data and so the programs may give different results. To minimize these differences, a thermochemical data base is being developed for use throughout the Nagra programme.

Nagra thermochemical data will be given in a series of reports, of which this is the first. This report describes the structure and construction of the data set and includes data for core species and minerals. Core data are for aqueous species, minerals, and gases of elements commonly found in natural waters. The data are considered to be well established. Data for other elements will be included in supplemental report, and may be subject to more frequent change.

This report includes core data for water and its components (H₂O, O₂ and H₂), the halides (F^-, CI^-, Br^- and I^-), sulphur (SO₄^2- and HS^-), nitrogen (NO₃^-, N₂ and NH₄⁺), phosphate (PO₄^3-), borate (B(HO)₃⁰), arsenic (AsO₄^3- and As(OH)₃⁰), carbon (CO₃^2-, C⁰ and CH₄), the alkaline earth metals (Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺), and the alkaline metals (Li⁺, Na⁺ and K⁺).