You can't put the design temperature, or any other temperature for that matter, in any of the Tx fields for the USER DEFINED material (material #21). The reason is that this is a completely user defined material, there is no information for CAESAR II to look up, like what the expansion coefficient is for a specified temperature. So for any temperature you want to analyze (design, operating 1, operating 2, etc), you have to input the corresponding expansion coefficient.