Experimental Investigation into the Elastic Buckling of a Nuclear Fuel Cladding Tube

Outer diameter of a dual cooled fuel rod needs to be increased considerably from that of a conventional one due to the requirement of a surface area increase as well as the formation of an internal flow passage. As was found previously, the thickness to outer diameter ratio (t/Do) of the conventional PWR fuel rod is mostly 0.058∼0.062. It seemed to be determined from experiences since there was little information about the reason for the t/Do values. Elastic buckling concern would be one of the reasons. Safety factor is more than 3 if a conventional design formula of the elastic buckling was applied. It is almost impossible to apply those values to a dual cooled fuel rod due to a considerably decreased rod-to-rod gap size and the amount of UO2 required for a burnup. So, there is a strong need to investigate the fundamental background of the used formula and its conservatism. In this paper, a classical theory of the stability was revisited and an experiment was conducted. Deduction for the used formula of an elastic buckling is explained. Experimental results are discussed by focusing on the safety margin of the used formula. Finally, the safety factor is considered for the presently determined thickness and diameter of a dual cooled fuel rod