The purpose of this paper is to verify that the design stress value of fuel rod for the irradiation test satisfies the structural design requirement. In this structural safety analysis thermal effect is the most severe element for the safety. The thermal effects are very complicated problem to be analyzed for the structural safety in short hand. By the application of theoretical analysis, the design margin of stress which was used in this fuel rod design was verified in the conservative point of view. In the future design of fuel rod, this analysis can be used as the theoretical method for the verification of safe design.