Thermal Analysis in UDEC

A thermal model comes standard in UDEC . This model simulates the transient flux of heat in materials and the subsequent development of thermally induced stresses. The heat flux is modeled by either isotropic or anisotropic conduction. Heat sources can be added and can be made to decay exponentially with time.

UDEC allows simulation of transient heat conduction in materials and the development of thermally induced displacements and stresses. This includes the following specific features.

  1. Heat transfer is modeled as conduction, either isotropic or anisotropic, depending on the user’s choice of material properties.
  2. Several different thermal boundary conditions may be imposed.
  3. Any of the mechanical block models may be used with the thermal model.
  4. Heat sources may be inserted into the material as volume sources. The sources may be made to decay exponentially with time.
  5. Both implicit and explicit calculations schemes are available, and the user can switch from one to the other at any time during a run.
  6. The thermal analysis provides one-way coupling to the mechanical stress calculation through the thermal expansion coefficient.
  7. The thermal analysis provides one-way coupling to the calculation for fluid flow in joints through the temperature dependency of fluid density and joint permeability.

The following example shows a transient thermal-mechanical simulation of the behavior of a nuclear-waste emplacement drift in which heat-producing waste is placed vertically beneath the panel floor (Christianson, 1989). The emplacement drift under study is in the center of an emplacement panel. Waste canisters are placed in the floor of the drift. Using model symmetry, only one-half of the disposal room-and-pillar needs to be included in the analysis. The thermal boundary conditions are considered to be adiabatic.

The tributary heating area for the emplacement panel is reported to be 8194.5 m2. The average thermal loading is considered to be 14.1 W/m2. For the panel geometry, this results in an initial heat-generating power per meter of room length of 713.5 W. The initial power of a waste container at the time of emplacement varies from 0.42 kW to 3.2 kW. The following UDEC model shows the rock mass around the panel with the temperate distribution and thermal-induced rock displacements after 50 years since waste emplacement.

White lines around the panel indicates where joints have slipped.

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