The ACP100, a small modular reactor designed and constructed in China, exemplifies an enhanced inherent safety profile by eliminating multiple design basis accidents through a compact primary loop and passive safety design principles. The strong interactions among the ACP100 systems necessitate an emphasis on pressure changes and other phenomena within the containment that may impact the accident transient. In this study, an analysis model for the ACP100 was established using a coupled platform of NUSOL-SYS and ISAA. A simulation of a double-ended guillotine break accident in the reactor pressurizer surge line was conducted to evaluate the safety performance of the ACP100 in such accidents. The simulation results demonstrate that the coupled calculation provide a more detailed insight than the decoupled calculation, including pressure variations and other phenomena within the containment. Although discrepancies in containment behavior lead to minor discrepancies in the performance of the primary loop and passive safety systems, these differences do not affect the main conclusions of the safety analysis. Following the accident, the passive safety systems of the ACP100 demonstrate the capability to effectively remove the decay heat, keeping the peak cladding temperature and peak containment pressure well below the limits.