Mass transfer and transport of radionuclides in fractured porous rock

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:7079641

Ahn, J

In the basic model, one-dimensional advection in a single planar fracture of infinite extent is coupled with diffusion in the rock matrix perpendicular to the fracture. Sorption and radioactive decay with no precursors are included. Matrix diffusion and radioactive decay make contaminant stay within some distance away from the source releasing contaminant for a finite period of time. Back diffusion is observed after the release period in the vicinity of the fracture entrance. Though enhancing early-time transport, longitudinal dispersion in the fracture may be neglected for long-term evaluations by assuming greater advection and fracture apertures than actual values. For multiple parallel fractures, the single-fracture model is still applicable for moderate overlap of concentration fields inside the rock matrix. Neglecting radioactive-decay precursors results in overly optimistic estimates of concentration in the fracture in early times. Transverse dispersion merges plumes released from individual waste forms in a repository. Mass transfer and transport from a cylindrical waste solid are studied in the cylindrical geometry by assuming molecular diffusion in the rock matrix parallel to, as well as perpendicular to the fracture, without advection. Radioactive decay enhances mass release from the cylinder. Even though the mass flux from the waste into rock is lower than to the fracture because of lower porosity, the larger waste surface exposed to the rock matrix and the greater matrix sorption can result in greater release rate to the matrix. With diffusion only, the basic model cannot be conservative against the cylinder model, with respect to the diffusive mass flux from the waste surface and to the distance that the contaminant can reach.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 7079641
• Country of Publication: United States
• Language: English

Related Subjects

052002* -- Nuclear Fuels-- Waste Disposal & Storage
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CYLINDERS
DECAY
DIFFUSION
ENVIRONMENTAL TRANSPORT
FRACTURED RESERVOIRS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOMETRY
MASS TRANSFER
MATERIALS
MATHEMATICAL MODELS
MATHEMATICS
NUCLEAR FACILITIES
ONE-DIMENSIONAL CALCULATIONS
POROSITY
POROUS MATERIALS
RADIOACTIVE WASTE FACILITIES
RADIONUCLIDE MIGRATION
RESERVOIR ROCK
SORPTION
TIME DEPENDENCE
WASTE FORMS