![]() ![]() For multiple more » 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. Many physical and chemical processes dominate the transport of radionuclides in groundwater. ![]()
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