Patent Number: 061987867
Section: claims

1. A method of controlling the system pressure in a power generating system comprised of a turbine-generator and a boiling water reactor, the boiling water reactor including a pressure vessel containing a nuclear fuel core, control rods, and a recirculation flow control system, the power generating system configured so that a core thermal power converts water into steam for driving the turbine-generator to produce electric power, and steam is converted back to water and returned to the boiling water in a closed loop, the turbine-generator includes main turbine control valves to control steam input into the turbine generator, the system pressure being controlled in a turbine control valve modulation pressure control mode, said method comprising the steps of: setting the main turbine control valves to a constant and steady position greater than 75% of wide open; and  controlling the system pressure to be within a predetermined range by utilizing a core thermal power modulation mode, the core thermal power modulation mode comprising adjusting the core thermal power of the reactor.  converting to a core thermal power modulation pressure control mode;  setting the main turbine control valves to a constant and steady position greater than 75% of wide open; and  controlling the system pressure to be within a predetermined range by adjusting the core thermal power of the reactor. 2. A method in accordance with claim 1 wherein setting the main turbine control valves to a constant steady position comprises the step of setting the turbine control valves to a wide open position. 3. A method in accordance with claim 1 wherein adjusting the core thermal power comprises the step of adjusting control rod density within the reactor core. 4. A method in accordance with claim 1 wherein adjusting the core thermal power comprises the step of adjusting the recirculation water flow rate through the reactor core. 5. A method in accordance with claim 4 wherein adjusting the recirculation water flow rate through the reactor core further comprises the step of adjusting the input to the recirculation flow control system. 6. A method in accordance with claim 5 further comprising the step of adjusting recirculation water flow by modulating a variable speed recirculation pump. 7. A method in accordance with claim 5 further comprising the step of adjusting recirculation water flow by modulating a recirculation water flow control valve. 8. A method in accordance with claim 1 further comprising the step of automatically modifying a bypass valve closure bias and a power control bias to accommodate variances from the reactor core thermal power modulation pressure control mode over the turbine control valve modulation pressure control mode. 9. A method in accordance with claim 1 further comprising the step of transferring system pressure control from the core thermal power modulation pressure control mode to the turbine control valve modulation pressure control mode when pressure transients are outside of a predetermined range. 10. A method of controlling the system pressure in a power generating system comprised of a turbine-generator and a boiling water reactor, the boiling water reactor including a pressure vessel containing a nuclear fuel core, control rods, and a recirculation flow control system, the power generating system configured so that core thermal power converts water into steam for driving the turbine-generator to produce electric power, and steam is converted back to water and returned to the boiling water reactor in a closed loop, the turbine-generator includes main turbine control valves to control steam input into the turbine-generator, the system pressure being controlled in a turbine control valve modulation pressure control mode, said method comprising the steps of: 11. A method in accordance with claim 10 wherein converting to the core thermal power modulation pressure control mode comprises the step of modifying a bypass valve closure bias and a power control bias to accommodate variances from the reactor core thermal power modulation pressure control mode over the turbine control valve modulation pressure control mode. 12. A method in accordance with claim 10 wherein setting the main turbine control valves to a constant steady position comprises the step of setting the turbine control valves to a wide open position. 13. A method in accordance with claim 10 wherein adjusting the core thermal power comprises the step of adjusting control rod density within the reactor core. 14. A method in accordance with claim 10 wherein adjusting the core thermal power comprises the step of adjusting the recirculation water flow rate through the reactor core. 15. A method in accordance with claim 14 wherein adjusting the recirculation water flow rate through the reactor core further comprises the step of adjusting the input to the recirculation flow control system. 16. A method in accordance with claim 15 further comprising the step of adjusting recirculation water flow by modulating a variable speed recirculation pump. 17. A method in accordance with claim 15 further comprising the step of adjusting recirculation water flow by modulating a recirculation water flow control valve. 18. A method in accordance with claim 10 further comprising the step of transferring system pressure control from the core thermal power modulation pressure control mode back to the turbine control valve modulation pressure control mode when pressure transients are outside of a predetermined range.