Heater model

[lecorrejm]

For power transients, a wall heat conduction module would be required to calculate the power to coolant. The model could be 1D (at a minimum) or 2D, geometry dependent (e.g., cylinder or flat) and multi-material (e.g., heater rods with cladding, insulation material, etc.). We need to think about how to seamlessly integrate this to the solver.