MOL.20060405.0097 zy MODELING COUPLED PROCESSES OF MULTIPHASE FLOW AND HEAT TRANSFER IN UNSATURATED FRACTURED ROCK zyxw Yu-Shu Wu', S. Mukhopadhyay', K. Zhang', and G. S. Bodvarssonl Earth Sciences Division, Lawrence Berkeley National Laboratory, MS 90-1 116 zy 1 Berkeley CA94720, USA ABSTRACT A mountain-scale, thermal-hydrologic (TH) numerical model is developed for investigating unsaturated flow behavior in response to decay heat from the radioactive waste repository at Yucca Mountain, Nevada, USA. The TH model, consisting of three-dimensional (3-D) representations of the unsaturated zone, is based on the current repository design, drift layout, and thermal loading scenario under estimated current and future climate conditions. More specifically, the TH model implements the current geological framework and hydrogeological conceptual models, and incorporates the most updated, best-estimated input parameters. This mountain-scale TH model simulates the coupled TH processes related to mountain-scale multiphase fluid flow, and evaluates the impact of radioactive waste heat on the hydrogeological system, including thermally perturbed liquid saturation, gas- and liquid-phase fluxes, and water and rock temperature elevations, as well as the changes in water flux driven by evaporatiodcondensation processes and drainage between drifts. For a better description of the ambient geothermal condition of the unsaturated zone system, the TH model is first calibrated against measured borehole temperature data. The ambient temperature calibration provides the necessary surface and water table boundary as well as initial conditions. Then, the TH model is used to obtain scientific understanding of TH processes in the Yucca Mountain unsaturated zone under the designed schedule of repository thermal load. 1. INTRODUCTION Since the 1980s, the 500-700 m thick unsaturated zone (UZ) of Yucca Mountain, Nevada, USA, has been extensively investigated as a potential subsurface repository for storing high-level radioactive wastes. While site characterization has been carried out mostly for analyzing unsaturated flow and tracer transport under ambient conditions (Wu et al., 1999; Wu et al. 2002), the inherent nature of nonisothermal flow and transport processes, created by repository heating from radioactive decay, has also motivated many research efforts to understand coupled thermal-hydrological (TH) behavior and its impact on repository performance within the UZ. In particular, significant progress has been made in quantitative TH modeling studies at Yucca Mountain (Haukwa et al. 1999; Haukwa et al. 2003; Buscheck et al. 2002). zyxwv 1