Example 1: For a fuel rod with length 3.7 m, pellet diameter 10 mm, no center hole, clad inner diameter 10.1 mm, and clad thickness 0.65 mm. Calculate the change of the fuel temperature with time if the generated heat is 60 kW/m and the rod is cooled by light water at 250oC and the clad to coolant HTC is 35 kW/m2K. Use the Lumped approach assuming the fuel initial temperature is equal to the coolant temperature. What is the fuel steady-state temperature and at what time it is reached. The UO2 and Zircaloy sp. heats are 0.3 and 0.4 kJ/kgK, respectively.
Example 2: Re-solve Example 1 neglecting clad heat capacity. What is the impact on the steady-state temperature and the time to reach steady-state.