Method and apparatus for protection of pump systems

This patent describes a nuclear power plant having a fluid-filler reactor vessel with a vapor outflow line for removing vapor from the reactor vessel, and liquid inflow means for injecting liquid to the reactor vessel. The inflow means includes an inflow line, a centrifugal pump disposed along the inflow line having an inlet and an outlet, an induction motor to drive the pump, flow control means along the inflow line between the pump and the reactor vessel from the pump. A means is included for generating a first control signal in response to liquid level in the reactor vessel and net vapor outflow versus liquid inflow with respect to the reactor vessel, the first control signal generating means being effective to generate a first signal to open and a second signal to close the flow control means to maintain liquid level in the vessel within predetermined limits. A pump and pump motor protection apparatus is described comprising: means for measuring the pressure of the liquid in the inlet of the pump; means for measuring the temperature of the liquid in the inlet of the pump; means for determining a required subcooling for the pump at the instantaneous temperature of the liquid in the inlet of the pump; and means for determining the enthalpy of the liquid in the inlet of the pump from the pressure and temperature of the liquid