Solute/Fluid Interaction Card Options (W)

The constant molecular diffusion option assumes that the effective diffusion coefficient in the porous media is equal to the free-water diffusion coefficient. For most simple aqueous species the free-water diffusion coefficient is about 10^-5 cm²/s (10^-9 m²/s).   

Symbols
	effective diffusion coefficient, m2/s
	free water diffusion coefficient, m2/s

In a saturated porous medium, the cross-sectional area available for diffusion in the aqueous phase is reduced by the porosity. In unsaturated porous media there is an additional reduction in cross-sectional area available for diffusion as a result of the reduced volumetric water content.

Symbols
	effective diffusion coefficient, m2/s
	free water diffusion coefficient, m2/s
	aqueous phase tortuosity
	actual aqueous liquid saturation
	diffusive porosity

No reaction occurs.

Decay or generation of solutes occurs in the STOMP simulator through an Arrhenius type kinetic reaction according to

The decay-rate constant can be related to the radionuclide half-life according to

Production of progeny solutes from parent solutes is computed through an Arrhenius type kinetic reaction according to

The chain decay fraction is a function of the parent-progeny pair, and the subscripts j and k indicate parent and progeny solutes respectively.

Symbols
	solute concentration of component i, 1/m3
	solute concentration of component j, 1/m3
	solute concentration of component k, 1/m3
	time, s
	radioactive decay constant of component i, 1/s
	radioactive decay constant of component j, 1/s
	radioactive decay half-life of component i, s
	chain decay fraction for radionuclide pair jk

Decay can also be simulated based on first-order and Monod chemical reactions. For first-order reactions, the reaction rate for each chemical reaction is dependent on the molar concentration of the primary reactant. The reaction rate factor is a function of the primary and secondary reactant molar concentrations, equation stoichiometry, reaction half-life, and simulation time step according to the following equations:

Symbols
	reaction rate factor
	component of reaction rate factor
	primary reactant concentration, 1/m3
	secondary reactant concentration, 1/m3
	moles of primary reactant pr
	moles of secondary reactant r
	time, s
	reaction half-life, s