Integral experiments simulating small-break loss-of-coolant accidents in the Westinghouse AP600 reactor are conducted using the ROSA-V large-scale test facility. These experiments show that the core makeup tank (CMT) behavior can be divided into two phases: the natural-circulation and the drain phases. The natural-circulation phase between the CMT and the rest of the primary is established immediately after the opening of the valve in the discharge line. The hot water from the primary, through the pressure balance line (PBL), accumulates in the top of the CMT, forming a clear thermal stratification above the cold initial inventory of the CMT. The drain phase is initiated by flashing in the CMT for break diameters ≤1 in. and by a gaseous flow from the primary for break diameters ≥2 in. Interactions between the CMT and the other safety components are observed: The CMT discharge rate is decreased by accumulator injection and is increased by actuation of the automatic depressurization system. When the PBL is empty of liquid, the CMT drain rate is approximately given by the free gravitational drain rate, irrespective of the flow direction in the PBL.