CORE MAKEUP TANK BEHAVIOR OBSERVED DURING THE ROSA-AP600 EXPERIMENTS

Integral experiments simulating small-break loss-of-coolant accidents in the Westinghouse AP600 reactor are conducted using the ROSA-V large -scale rest facility. These experiments show that the core makeup tank (CMT) behavior can be divided into two phases: the natural-circulatio n and the drain phases. The natural-circulation phase between the CMT and the rest of the primary is established immediately after the openi ng of the valve in the discharge line. The hot water from the primary, through the pressure balance line (PBL), accumulates in the top of th e CMT, forming a clear thermal stratification above the cold initial i n ventory of the CMT. The drain phase is initiated by flashing in the CMT for break diameters less than or equal to 1 in. and by a gaseous f low from the primary for break diameters greater than or equal to 2 in . Interactions between the CMT and the other safety components are obs erved: The CMT discharge rate is decreased by accumulator injection an d is increased by actuation of the automatic depressurization system. When the PBL is empty of liquid, the CMT drain rate is approximately g iven by the free gravitational drain rate, irrespective of the flow di rection in the PBL.