Yucca Mountain Project Preclosure Ventilation Heat Transfer Analysis: Solution Method and Results

The thermal energy balance for emplacement drift ventilation is solved analytically by using “well-mixed” volume elements that discretize the domain down the length of a drift. The solution technique is based on the use of a lumped parameter quasi-steady-state approximation, and the principle of superposition. The lumped parameters are convective and linearized radiation heat transfer coefficients. The quasi-stead-state approximation allows the energy balance equations to be written without time derivatives and solved algebraically for a single time step. The progress of the heat transfer analysis through time is like that of integrating a function using Euler’s method. The principle of superposition is used to calculate the temperature response of the drift wall due to an arbitrary heat flux and a given set of thermophysical rock properties. The results of this calculation are used as a “multiplier” on the drift wall heat flux in the algebraic solution of the four energy balances, and eliminates the need to solve the conduction heat transfer in the rock mass at every time step. The results of the analysis are compared to a similar numerical model and include time and location dependent waste package, in-drift air, and drift wall temperatures, and ventilation efficiencies.