Control system for a nuclear steam power plant

A control system for a nuclear steam power plant having a nuclear reactor, a once through steam generator, means circulating coolant between the nuclear reactor and the once through steam generator including a hot coolant pipe, a cold coolant pipe and coolant pump means, means supplying feedwater to the once through steam generator including feedwater flow regulating means for controlling feedwater supplied to the once through steam generator, a turbine driven by steam generated by the once through steam generator and means supplying steam from the once through steam generator to the turbine including governor valve means for controlling the amount of steam supplied to the turbine, said control system comprising

• a reactor control subsystem including reactor demand means for receiving an input from an operator representative of a selected power demand for the nuclear steam power plant and producing an output representative of reactor demand required to achieve said selected power demand for the nuclear steam power plant, rod control means responsive to said reactor demand output from said reactor demand means to control operation of the nuclear reactor, and reactor demand limit means supplying an input to said reactor demand means to limit said reactor demand output;
• a feedwater control subsystem independent of said reactor control subsystem including means for controlling the feedwater flow regulating means to control the flow of feedwater supplied to the once through steam generator, temperature sensing means for sensing the temperature of coolant in the hot coolant pipe and the temperature of coolant in the cold coolant pipe, means for sensing operation of the coolant pump to produce a coolant flow signal, and computing means responsive to the difference in the coolant temperatures in the hot coolant pipe and the cold coolant pipe and to said coolant flow signal to produce a thermal power delivered output signal for controlling the feedwater flow regulating means such that the flow of feedwater to the once through steam generator is controlled in response to the thermal power delivered by the nuclear reactor;
• a turbine steam demand control subsystem independent of said reactor control subsystem and said feedwater control subsystem including pressure sensing means for sensing steam pressure in the means for supplying steam to the turbine, means providing a turbine steam pressure setpoint and means responsive to deviation of said steam pressure from said turbine steam pressure setpoint for controlling the governor valve means to maintain said steam pressure substantially at said turbine steam pressure setpoint and for controlling the turbine in response to steam generated by the once through steam generator whereby said feedwater control subsystem controls feedwater flow to match the thermal power delivered by the once through steam generator to the thermal power delivered by the nuclear reactor, independent of said reactor control subsystem by controlling the feedwater flow regulating means and said turbine steam demand control subsystem controls the turbine in accordance with said steam pressure independent of said reactor control subsystem and said feedwater control subsystem.