Effect of deformation and loss-of-seal on the embrittlement of VVER fuel-element cladding in loss-of-coolant accidents

The structural-phase state and residual lifetime of the mechanical properties in the regions where VVER fuel element cladding has become unsealed after tests on the PARAMETR stand under loss-of-coolant accident conditions are investigated. It is determined that deformation engenders breaks in the oxide film which promote oxidation. The structural and strength characteristics in the region of unsealing exhibit strong azimuthal nonuniformity, which is due to the nature of the deformation, thinning of the cladding wall, and the degree of damage to the oxide as result of deformation. The results presented show that it is very important to examine the processes leading to the deformation of fuel element cladding and the subsequent behavior of the regions of unsealing in a corrosive medium from the standpoint of the formation of the most vulnerable zone, which is responsible for the residual lifetime of the entire fuel element.