In order to improve fast reactor performance, optimization of the design margin is required. Consequently, a probabilistic method for fuel rod design is being considered, and the Baysian Oriented Fuel Rod Performance Evaluation (BORNFREE) probabilistic code, which computed the statistical responses of several performance parameters concerning fuel rod integrity, was developed. The probability that the performance parameter exceeds the criterion and the design margin can be quantitatively estimated by using this code. In this study, uncertainties that affect the cladding stress, which is one of the performance parameters that restricts the lifetime of a fuel rod, were statistically simulated, and the probabilistic results were compared with the deterministic results of the conventional method. As a result of the trial computation, it was confirmed that the deterministic results were adequately conservative and exceeded the 3 upper level of the probabilistic results for any case. Furthermore, the deterministic results showed significant overestimation as compared with the probabilistic results. Consequently, it is suggested that the probabilistic method is a feasible option to optimize the design evaluation to expand the lifetime of a fuel rod.