The natural system is an integral part of a geologic nuclear waste repository; it extends from the disturbed rock zone (DRZ) around a disposal room, created by mechanical, thermal and chemical perturbations due to underground excavation or waste emplacement, to the surrounding geologic media, and out to a specified repository boundary. The natural system evaluation and tool development work supports anticipated future site screening, site selection, site characterization, and site suitability. This work is conducted to reduce uncertainty in natural system performance and to fully exploit the credits that can be taken for the natural system barrier. This report examines information developed for: 1) iodide interactions with clay minerals with results suggesting that iodide may directly interact with clays by forming ion-pairs which may concentrate within the interlayer space as well as the thin areas surrounding the clay particle; 2) the Small-Angle Neutron Scattering (SANS) used to characterize the pore features of various clay and shale samples to better characterize radionuclide transport in low-permeability clay materials; 3) the combined use of the batch and column uranium transport experiments using granitic material to provide constraints on adsorption and desorption kinetics; 4) formation of Pu oxides and interaction of clay and Intrinsic Pu colloids; 5) modeling of Pu transport in clay material; 6) examination of the thermal limit for clay minerals in a nuclear waste repository; and 7) examination of a variety of clays [e.g., illite, smectite] over temperature range of 100-500 °C and characterized for surface area, pore structure, and cation exchange capacity. The work is intended to culminate in providing defensible, enhanced and transparent conceptual and mathematical models for total system performance assessments.