High temperature NPSH and its application for a feedwater system

Eight hundred MWe class PWR turbine-generators operated smoothly and continuously at sudden load reduction from full load to house load, maintaining NPSH of the feedwater booster pumps through transition even though the available NPSH never exceeded zero. NPSH of the pump at 151.3°C, at which the available NPSH was minimal during transition, was evaluated as a slightly negative value, in spite of a positive value at room temperature, applying both the Ruggeri-Moore method extended to the negative area on condition of gas venting out of the system, using data of both room temperature and 95°C of a model pump facility, and another restriction by gas presence at the impeller inlet. The above evaluated high temperature NPSH demonstrated successful operation of the units equipped with a low static suction head yielding zero available NPSH during transition, resulting in alteration of the design criteria of the feedwater system and thereby contributing to possible cost reduction.