Thickness Assessment for Accident-Tolerant FeCrAl Fuel Cladding Based on Elastoplastic and Creep Buckling Analyses

FeCrAl alloy cladding is considered to be one of the most promising candidates for near-term application in the accident-tolerant fuel (ATF) framework. However, it has a higher neutron absorption cross section compared with conventional Zircaloy cladding, and its thickness tends to be reduced to maintain the neutron economy. Structural stability may be lost if the thickness cannot withstand the high external pressure during reactor operations.Therefore, the present study assesses the minimum allowable thickness of the ATF FeCrAl cladding based on mechanical integrity to prevent a cladding collapse under normal operating conditions. A finite-length C35M FeCrAl alloy cylindrical shell model with various initial ovalities was developed. The elastic, elastoplastic, and creep buckling features were further revealed by a finite element analysis, where the cladding collapse from the long-term effects of thermal creep and irradiation creep were of great concern.It was indicated that the creep lifetime of the cladding that satisfies the elastic or elastoplastic buckling requirements may not meet the operating requirement. For the case of a creep lifetime of 3 years and a pressure difference of 11 MPa, cladding with a minimum thickness of 0.4423 mm (with 0.5% ovality) would be required. A reference diagram of the minimum thickness necessary to prevent a creep buckling failure corresponding to variations in the creep lifetime, the initial ovality, and the pressure difference is provided.