ISLAND MODE FOR NUCLEAR POWER PLANT

• US 20130272471A1
• Filed: 04/11/2013
• Published: 10/17/2013
• Est. Priority Date: 04/17/2012
• Status: Active Grant

• Current Assignee: Bwxt Mpower, Inc.
• Original Assignee: Bwxt Mpower, Inc.
• Inventors: GRAHAM, Thomas G.
• Granted Patent: US 9,620,252 B2
• Time in Patent Office: Days
• US Class Current: 376/277
• CPC Class Codes: G21C 9/00 Emergency protection arrangements structurally associated with the reactor , e.g. safety valves provided with pressure equalisation devicesemergency cooling arrangements G21C15/18
• CPC Class Codes: G21D 1/02 Arrangements of auxiliary equipment
• CPC Class Codes: G21D 3/04 Safety arrangements emergency protection of reactor G21C9/00
• CPC Class Codes: Y02E 30/00 Energy generation of nuclear origin
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

A nuclear power plant comprises a pressurized water reactor (PWR) and a steam generator driving a turbine driving an electric generator. A condenser condenses steam after flowing through the turbine. Responsive to a station blackout, the nuclear power plant is electrically isolated and a bypass valve is opened to convey bypass steam flow from the steam generator to the condenser without flowing through the turbine. The thermal power output of the PWR is gradually reduced over the transition time interval. After opening, the bypass valve is gradually closed over the transition time interval. A supplemental bypass valve may also be opened responsive to the station blackout to convey supplemental bypass steam flow from the steam generator to a feedwater system supplying secondary coolant feedwater to the steam generator. The supplemental bypass steam flow does not flow through the turbine and does not flow through the condenser.

Claims

1. A nuclear power plant comprising:

a nuclear reactor comprising a pressurized water reactor (PWR) and a steam generator configured to transfer heat from primary coolant water heated by the PWR to secondary coolant water in order to convert the secondary coolant water to steam;

a turbine connected with the steam generator to be driven by steam output by the steam generator;

an electric generator connected with the turbine to be driven by the turbine to generate electricity;

an electrical switchyard receiving electrical power from the electrical power generator during normal operation of the nuclear power plant;

a condenser connected with the turbine to condense steam exiting the turbine; and

a turbine bypass system configured to transfer a quantity of steam output by the steam generator to the condenser without passing through the turbine responsive to loss of offsite electrical power to the nuclear power plant wherein the quantity of steam transferred to the condenser without passing through the turbine is effective to (1) allow the nuclear reactor to power down without triggering steam generator or nuclear reactor pressurizer safety valve setpoints and (2) continue powering house electrical loads of the nuclear power plant using the turbine.

2. The nuclear power plant of claim 1 wherein the turbine bypass system is further configured to disconnect the electric generator from the electrical switchyard responsive to loss of offsite electrical power.

3. The nuclear power plant of claim 1 wherein the turbine bypass system includes a bypass valve that initially opens responsive to loss of offsite electrical power and then gradually closes over a transition time interval.

4. The nuclear power plant of claim 3 wherein the turbine bypass system does not vent steam to atmosphere.

5. The nuclear power plant of claim 3 wherein the bypass valve initially fully opens responsive to loss of offsite electrical power, gradually closes over a transition time interval, and is fully closed at the end of the transition time interval.

6. The nuclear power plant of claim 3 wherein the PWR is configured to gradually reduce its thermal power output to a minimum reactor load level over the transition time interval.

7. The nuclear power plant of claim 6 wherein the minimum reactor load level is 20% or less of the thermal power output by the PWR before loss of onsite electrical power.

8. The nuclear power plant of claim 1 wherein the turbine bypass system includes:

a bypass valve controlling a bypass line configured to transfer a quantity of steam output by the steam generator to the condenser without passing through the turbine; and

a supplemental bypass valve controlling a supplemental bypass line configured to transfer a quantity of steam output by the steam generator to a feedwater system of the PWR without passing through the turbine and without passing through the condenser.

9. The nuclear power plant of claim 1 wherein the PWR is an integral PWR and the steam generator is disposed inside a pressure vessel of the PWR.

10. A method of operating a nuclear power plant that includes a pressurized water reactor (PWR), a steam generator, a turbine, an electric generator, and a condenser, the method comprising:

operating the PWR to heat primary coolant flowing through a nuclear reactor core comprising fissile material immersed in the primary coolant water;

operating the steam generator to convert secondary coolant feedwater to steam using primary coolant water heated by the operating PWR;

operating the turbine by flowing steam from the steam generator through the turbine and then through the condenser;

driving the electric generator using the turbine to generate electricity;

conveying the generated electricity to an electrical switchyard; and

responsive to a station blackout, transitioning the nuclear power plant to an island mode over a transition time interval by transition operations including;

at the beginning of the transition time interval, disconnecting the electric generator from the electrical switchyard and opening a bypass valve to convey bypass steam flow from the steam generator to the condenser wherein the bypass steam flow does not flow through the turbine;

after opening the bypass valve, gradually closing the bypass valve over the transition time interval; and

gradually reducing the thermal power output of the PWR over the transition time interval.

11. The method of claim 10 further comprising:

concurrently with conveying the generated electricity to the electrical switchyard, also conveying the generated electricity to an electrical power system of the nuclear power plant; and

in the transitioning, continuing to convey the generated electricity to the electrical power system of the nuclear power plant after the disconnecting of the electric generator from the electrical switchyard.

12. The method of claim 11 wherein the gradual reducing comprises gradually reducing the thermal power output of the PWR over the transition time interval such that the thermal power output of the operating PWR at the end of the transition time interval is 20% or less of the thermal power output of the operating PWR before the transition time interval.

13. The method of claim 11 wherein the gradual closing of the bypass valve over the transition time interval comprises:

controlling the bypass valve over the transition time interval to convey bypass steam flow from the steam generator to the condenser that is sufficient to enable said gradual reducing of the thermal power output of the PWR over the transition time interval without approaching steam generator or pressurizer safety valve setpoints and while continuing to convey the generated electricity to the electrical power system of the nuclear power plant after the disconnecting of the electric generator from the electrical switchyard.

14. The method of claim 10 wherein the transition operations further include:

at the beginning of the transition time interval, opening a supplemental bypass valve to convey supplemental bypass steam flow from the steam generator to a feedwater system of the PWR wherein the supplemental bypass steam flow does not flow through the turbine and does not flow through the condenser.

15. The method of claim 14 wherein the transition operations further include:

after opening the supplemental bypass valve, gradually closing the supplemental bypass valve over the transition time interval.

16. The method of claim 10 wherein the transition operations do not include venting the steam from the steam generator to atmosphere.

17. The method of claim 10 wherein the operating of the steam generator includes:

disposing the steam generator inside a pressure vessel of the PWR; and

flowing the secondary coolant feedwater into a feedwater inlet of the PWR and through the steam generator where primary coolant water heated by the operating PWR heats the secondary coolant feedwater to convert the secondary coolant feedwater to steam that exits a steam outlet of the PWR.

18. The method of claim 10 wherein the gradual closing of the bypass valve over the transition time interval results in the bypass valve being fully closed at the end of the transition time interval.

19. A method operating in conjunction with a nuclear power plant comprising a pressurized water reactor (PWR) operating to heat primary coolant water, a steam generator using the heated primary coolant water to convert secondary coolant feedwater to steam, a turbine driven by steam from the steam generator and operatively connected with an electric generator, and a condenser connected with the turbine to condense steam after flowing through the turbine, the method comprising:

transitioning the nuclear power plant to an island mode over a transition time interval by transition operations including;

responsive to detecting a station blackout, electrically isolating the nuclear power plant and opening a bypass valve to convey bypass steam flow from the steam generator to the condenser without flowing through the turbine; and

gradually reducing the thermal power output of the PWR over the transition time interval.

20. The method of claim 19 wherein the transition operations further include:

after opening the bypass valve, gradually closing the bypass valve over the transition time interval.

21. The method of claim 19 wherein the transition operations further include:

responsive to detecting the station blackout, opening a supplemental bypass valve to convey supplemental bypass steam flow from the steam generator to a feedwater system supplying the secondary coolant feedwater to the steam generator;

wherein the supplemental bypass steam flow does not flow through the turbine and does not flow through the condenser.

22. The method of claim 19 wherein the transition operations do not include venting steam from the steam generator to atmosphere.

23. The method of claim 19 wherein the transition operations further include conveying electricity generated by the generator to an electrical power system of the nuclear power plant during the transition time interval, the method further comprising:

After the transition time interval, continuing to convey electricity generated by the generator to an electrical power system of the nuclear power plant.

24. The method of claim 19 wherein the gradual reducing of the thermal power output of the PWR over the transition time interval comprises:

gradually reducing the thermal power output of the PWR over the transition time interval to a level that is 20% or less of the thermal power output of the PWR prior to detecting the station blackout.