Analysis of Pellet-Clad Mechanical Interaction Process of High-Burnup PWR Fuel Rods by RANNS Code in Reactivity-Initiated Accident Conditions

Exploratory analyses were performed by the RANNS code for simulated tests of the reactivity-initiated accident with two high-burnup pressurized water reactor rods in the Nuclear Safety Research Reactor (NSRR). The code performs thermal and finite element mechanical calculations in an axis-symmetrical cylinder geometry. On the basis of the irradiation-induced rod conditions including bonding, the code analyzed a strong pellet-clad mechanical interaction process that would often lead to low-strain split failure. The predicted quantities such as temperature and stress strain of cladding were discussed and compared with the experimental observations. The calculated cladding permanent strain has a reasonable agreement with postirradiation examination data. The process from crack initiation to final split failure was accounted for by the plastic strain occurrence in the cladding.