China initiative Accelerator Driven System (CiADS) is a 10 MW lead–bismuth eutectic (LBE) cooled subcritical reactor, which is designed to demonstrate the engineering feasibility of the ADS concept. An elaborated methodology was developed to deal with the nonlinear mechanical behaviors of fuels under transients. Based on this methodology, the fuel mechanical module was accomplished and coupled with the neutron dynamics module and thermo-hydraulics module in the extended BELLA code. The cladding mechanical simulation under frequent beam trips for CiADS was carried out using BELLA, and fatigue analysis based on the experimental data was discussed. Combined with the CiADS beam-trip transients, it is concluded that the tolerance of the CiADS cladding to beam trips is between 1000 and 11,000 cycles.