Marfa: Radionuclide Transport in the Subsurface
Marfa simulates migration, retention, decay, and ingrowth of radionuclides beneath the surface of the Earth. The primary application is for safety assessments of potential repositories for radioactive wastes.
Marfa is designed to be very efficient for large-scale applications that involve many radionuclides, discrete source locations, and transport pathways with a high degree of spatial variability. It was specifically designed to handle the high degree of spatial complexity associated with transport pathways through stochastically generated discrete fracture networks (DFNs).
Marfa is based on a unique Monte Carlo algorithm called time-domain random walk particle tracking. Theoretical background has been published elsewhere. A summary can be found in Posiva Working Report 2013-1.
MARFA represents the following physical processes:
- Longitudinal dispersion and molecular diffusion in fractures
- Matrix diffusion in an infinite or finite matrix.
- Equilibrium sorption.
- Decay and ingrowth.
- Colloid-assisted transport.
Significantly, MARFA supports full heterogeneity in the pathway. That is, a pathway may include sections in fractures, backfilled tunnels, buffer, deformation zones, soil, etc., in any order or combination.
In addition, MARFA has a unique downscaling algorithm that attempts to recover the transport effects of velocity variability that were averaged away during flow upscaling. Theory and motivation are describe in Painter et al. (2005).
Marfa has been actively developed since 2006 and several versions are available.
Two variants of Marfa are in use. One simulates transport on fixed transport pathways extracted from a steady flow field. Although that version uses fixed or static pathways, the groundwater speed along those pathways may be specified as user input in a piecewise steady approximation. The other variant uses a node-routing approximation that accommodates fully transient groundwater velocities.
The 3.0 series
The 3.2 series (fixed pathways) and 3.3 series (node routine variant) were used until late 2014. Those versions expected parameter groupings as input for the transport properties, as described in the Users Manual for 3.x. In addition, those versions had limited capability to model changes in radionuclide Kd values. The 3.2.4 and 3.3.1 were used previously in applications and are still available.
Starting around 2014, MARFA input was changed to require physical properties rather than groupings of those parameters. This change was for transparency and usability reasons. In addition, more flexible representation of transient Kd's was added. Moreover, the static-pathways and node-routing versions were partially merged. Those two variants of the code share much of the same code base and the code was reorganized to take advantage of that. Version 4.3 can be found here. The static-pathway (sp) and node-routing (nr) variants can be found in separate subdirectories within that repository. A user manual for Version 4.3 can be found here.
Marfa 5.x (latest)
In early 2020, MARFA 5.0 was released. The input files formats were slightly modified for greater flexibility. In addition, the capability to simulate diffusion into stagnant water was added. New verification tests were created and the example simulations were updated. Version 5.0 can be found here. The user manual can be found here.
Marfa developer version
The current developer version may be found here.
Software validation tests
Software validation (as opposed to model validation) was described in detail in the user's manual for the 3.x series. Software validation tests are maintained with the repository for each version. These tests have been updated to remain current with changing input formats. New tests were added as new capability was introduced. A summary of the current suite of tests is available.