A Power-Rate-Dependent Model for Pellet/Cladding Mechanical Interaction

A loading-rate-dependent model has been developed for the analysis of pellet/cladding mechanical interaction that takes the power ramp rate into account. Based on knowledge of the local strain rate behavior, the effect of ramp rate on fuel rod performance is well described by using the strain energy density criterion. The threshold value of the strain energy density for fuel cladding is determined from the Studsvik Inter-Ramp Project experimental data in conjunction with stress analysis. The critical strain energy density for recrystallized Zircaloy-2 is found to be 0.32 MPa. With this value, the damage zone of cladding for a specific fuel rod design under various burnups, ramp rates, and ramped terminal linear heat generation rates can be established, and the ramp rate effect is well identified.