MMT, 1-D Radionuclide Groundwater Transport

1 - Description of program or function: MMT (Multicomponent Mass Transport) solves the one-dimensional equation for transport of radionuclides in a ground-water system with uniform velocity and transport properties. The purpose of the code is to evaluate radionuclide release rates from the site subsystem. MMT treats convective transport, sorption-desorption effects, and hydrodynamic dispersion. Sorption and desorption of radionuclides are taken into account by application of retardation factors which are spatially uniform and derived from bulk rock properties and average geochemical data. Dispersion along the direction of flow (forward and backward) is also taken into account. 2 - Method of solution: Because the code solves only the one- dimensional transport equation, dispersion transverse to the direction of flow is not evaluated. A discrete-parcel-random-walk (DPRW) approach is used to solve the coupled equations. This numerical technique is inherently stable and minimizes computational errors that lead to apparent mass nonconservation