Simulation of Ventilation Efficiency, Temperatures, and Relative Humidities in Emplacement Drifts at Yucca Mountain, Nevada, Using Monte Carlo and Composite Thermal-Pulse Methods
Predictions of waste canister and repository driftwall temperatures as a function of space and time are of fundamental importance to evaluating pre-closure and postclosure design requirements and performance assessment of the proposed repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. Variations in the lithostratigraphic features in densely welded and crystallized rocks of the 12.8-million-year-old Topopah Spring Tuff, especially the porosity resulting
... porosity resulting from lithophysal cavities, are projected 50 to 800 m from the Enhanced Characterization of the Repository Block cross drift to a simulated "Panel 1" emplacement drift. Lithophysal cavity porosity varies from 0.00 to 0.05 cm3/cm3 in the middle nonlithophysal zone and from 0.03 to 0.28 cm3/cm3 in the lower lithophysal zone. Many thermal properties are related to lithophysal cavity porosity, and computer code titled "Monte Carlo Simulation of Ventilation" (MCSIMVENT) has been developed for simulating statistical variability and uncertainty along the simulated emplacement drift. The MCSIMVENT code, which is based on a composite thermalpulse calculation, is used to calculate pre-closure ventilation efficiency and peak post-closure temperatures and relative humidities along the simulated emplacement drift for as much as 1,000 years. Variations in lithophysal porosity along the drift can result in a range in peak waste-package temperatures from 160 to 180 "C for a single emplacement drift.