A thermal-hydraulic integral-effect test facility [advanced thermal-hydraulic test loop for accident simulation (ATLAS)] is being constructed at the Korea Atomic Energy Research Institute. The ATLAS is a one-half-reduced-height and 1/288-volume-scaled test facility based on the design features of the APR1400, an evolutionary pressurized water reactor developed by the Korean industry. The simulation capability of the ATLAS for major design-basis accidents (DBAs), including a large-break loss-of-coolant accident and direct vessel injection line-break and main-steam-line-break accidents, is evaluated by the best-estimate system code MARS with the same control logics, transient scenarios, and nodalization scheme. The validity of the applied scaling law and the thermal-hydraulic similarity between the ATLAS and the APR1400 for the major DBAs are assessed. It is confirmed that the ATLAS can maintain an overall similarity with the reference plant APR1400 for the major DBAs considered in the study. However, depending on the accident scenarios, there are some inconsistencies in certain thermal-hydraulic parameters, such as cladding temperature, subcooling at the lower plenum of the core, break flow rate, core and downcomer water level, and secondary pressure. The causes of the inconsistencies are carefully investigated by considering the detailed design features of the ATLAS. It is found that the inconsistencies are mainly due to the reduced power effect and the increased stored energy in the structure. The similarity analysis was successful in obtaining a greater insight into the unique design features of the ATLAS and would be used for developing optimized experimental procedures and control logics.