A thermal-hydrologic natural-ventilation model is configured for simulating temperature, humidity, and condensate distributions in the coupled domains of the in-drift airspace and the near-field rock mass in the proposed Yucca Mountain repository. The multiphysics problem is solved with MULTIFLUX, in which a lumped-parameter computational fluid dynamics (CFD) model is iterated with TOUGH2. The iterative process ensures that consistent boundary conditions are used on the drift wall in both the CFD and the TOUGH2 model-elements. The CFD solution includes natural convection, conduction, and radiation for heat, as well as moisture convection and diffusion for moisture transport with half waste package-scale details in the drift. The TOUGH2 solution for the rock mass is generalized with the use of the Numerical Transport Code Functionalization technique in order to include both mountain-scale heat and moisture transport in the porous and fractured rock, and fine half waste package-scale details at the drift wall. The method provides fast convergence on a personal computer computational platform. Numerical examples and comparison with a TOUGH2-based integrated model are presented.