The behavior of the primary system coolant in a pressurized water reactor during a small-break loss-of-coolant accident (LOCA) is governed by the hydrostatic forces that develop in the system. Digital simulation of the hydrostatic interactions during a small-break LOCA can be achieved with simplified nodal representations that significantly reduce computer times. The simplification process can be successfully achieved by combining primary system regions that behave symmetrically while preserving the basic manometer or U-tube design of the system. The simplified nodal representations have the capability of assessing the hydrostatic effects on the blowdown for the spectrum of small breaks wherein detailed model computations become economically prohibitive for parametric analyses of emergency core cooling systems.