Solute/Fluid Description (G)
Overview
This card is used to define solute properties, including radioactive decay reactions, first-order reactions and molecular diffusion. Solute/fluid interaction parameters such as molecular diffusion coefficients and interface partition coefficients depend on the operational mode. Molecular diffusion coefficients represent solute diffusion through the transporting fluid phase, independent of the porous media. Corrections for transport through porous media are handled within the simulator. For the empirical and power function models of diffusion, parameters for these models are not entered on this card, but in the Solute/Porous Media Interactions Card. Although partition coefficients (i.e., Kd) are a property of the solute, they are also a property of the porous media since they define the equilibrium distribution of solutes between active liquid and solid phases. Hence, partition coefficients are defined on the Solute/Porous Media Interaction Card.
Radioactive Decay
Solutes can decay radioactively to produce other solutes. For the loose coupling between parent solutes and progeny solutes to function properly, parent solutes must be defined on this card prior to their progeny. The simulator actually solves the transport equation for each solute sequentially in reverse order from the definition list on this card. Solutes are defined by a unique solute name, which must contain no more than 64 characters. Chain Decay Fraction relates a parent decay member with a progeny and refers to the fraction of the decaying parent that produces a particular progeny. Chain Decay Fraction inputs should be fractional values between 0.0 and 1.0, inclusively.
First-Order Reactions
Solutes can be transformed to produce other solutes using first-order or Monod-type kinetics. In a first-order reaction, the reaction rate is directly proportional to the concentration of the solute. The reaction rate for each chemical reaction is dependent on the molar concentration of the primary and secondary reactant molar concentrations, equation stoichiometry and reaction half-life. Solute conservation equations are solved sequentially with daughter solutes preceding parent or primary reactant solutes.