Effective continuum approximation for modeling fluid and heat flow in fractured porous tuff: Nevada Nuclear Waste Storage Investigations Project
Fluid and heat flow in fractured porous media can be of great complexity, and a quantitative description requires the development of simplified mathematical and numerical methods. This report presents a detailed formulation, and partial evaluation, of an ``effective continuum approximation`` for non-isothermal multi-phase flow, which had been introduced previously only in a heuristic fashion. The key concept on which the effective continuum approach must rely is (approximate) local thermodynamic equilibrium between fractures and rock matrix. The applicability of this approximation is discussed and studied by means of numerical simulations for emplacement of high-level waste packages in partially saturated fractured tuff. The simulations demonstrate that the validity of the effective continuum approximation cannot be ascertained in general terms. The approximation will break down for rapid transients in flow systems with low matrix permeability and/or large fracture spacing, so that its applicability needs to be carefully evaluated for the specific processes and conditions under study. The effective continuum approximation has been applied for a preliminary study of fluid and heat flow near a high-level nuclear waste repository on a regional scale, employing a highly simplified strtatigraphic description. It was found that substantial gas phase convection was taking place, with convection velocities being sensitive to permeability, porosity, and tortuosity of the fracture network. 18 refs., 27 figs., 7 tabs.
- Research Organization:
- Lawrence Berkeley Lab., CA (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 60449
- Report Number(s):
- SAND--86-7000; ON: DE88010969
- Country of Publication:
- United States
- Language:
- English
Similar Records
Numerical modeling of multiphase and nonisothermal flow in fractured media
On thermohydrologic conditions near high-level nuclear wastes emplaced in partially saturated fractured tuff. 1. Simulation studies with explicit consideration of fracture effects