Patent Number: 
Section: claims

1. A generation system comprising:a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor;a high-pressure turbine connected to said natural circulation reactor by a main steam pipe configured to at least introduce steam generated in said natural circulation reactor to said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine;a low-pressure turbine configured to receive steam exhausted from said high-pressure turbine;a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine and configured to at least receive steam exhausted from said high-pressure turbine;a first steam control valve installed in said main steam pipe at a position between the one end of the main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine;an inlet pipe having a second steam control valve installed in said inlet pipe, said inlet pipe having one end of said inlet pipe connected to said main steam pipe at a position between said natural circulation reactor and said first steam control valve installed in said main steam pipe, and said inlet pipe having another end of said inlet pipe connected to said moisture separation heater, said second steam control value being installed at a position between the one end of said inlet pipe connected to said main steam pipe and the another end of said inlet pipe connected to said moisture separation heater;a control rod drive apparatus connected with a control rod configured to be inserted and withdrawn with respect to a core of said natural circulation reactor;a power control apparatus adapted to output a power adjustment demand signal and a control rod drive command signal based on a reactor power detected by a reactor power detector configured to detect reactor power;a control rod drive control apparatus adapted to control said control rod drive apparatus based on said control rod drive command signal; anda pressure control apparatus adapted to control a pressure of said natural circulation reactor;wherein said pressure control apparatus is adapted to control a degree of opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal, and is adapted to control a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 2. The generation system according to claim 1, wherein any one of said pressure control apparatus and said power control apparatus is adapted to input a load following demand signal from a center feeding chamber. 3. The generation system according to claim 2, wherein said first steam control valve installed in said main steam pipe is installed in said main steam pipe upstream of said high-pressure turbine;wherein said inlet pipe has the one end connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe; andwherein said pressure control apparatus controls a degree of opening of said steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe when said load following demand signal has a narrow range and a short period. 4. The generation system according to claim 1, wherein a turbine bypass pipe is connected to said main steam pipe upstream of said high-pressure turbine and to a condenser configured to receive steam exhausted from said low-pressure turbine;wherein a turbine bypass valve is installed in said turbine bypass pipe; andwherein said pressure control apparatus is adapted to control a degree of opening of said turbine bypass valve jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe. 5. The generation system according to claim 4, wherein said pressure control apparatus has a gate portion, and controls said turbine bypass control valve to open when said power adjustment demand signal is greater than a preset threshold, and controls said second steam control valve installed in said inlet pipe to close when said power adjustment demand signal is smaller than said preset threshold. 6. The generation system according to claim 1, wherein a turbine bypass pipe is connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe and to a condenser adapted to receive steam exhausted from said low-pressure turbine;wherein a turbine bypass valve is installed in said turbine bypass pipe; andwherein said pressure control apparatus is adapted to control a degree of opening of first said steam control valve installed in said main steam pipe and a degree of opening of said turbine bypass valve jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe. 7. The generation system according to claim 6, wherein said pressure control apparatus has a gate portion, and controls said turbine bypass control valve to open when said load following demand signal is greater than a preset threshold, and controls said second steam control valve installed in said inlet pipe to close when said load following demand signal is smaller than the preset threshold. 8. The generation system according to claim 1, wherein when a variation in the reactor power of said natural circulation reactor is transient, said pressure control apparatus is adapted to control the degree of the opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal. 9. The generation system according to claim 1, wherein said power control apparatus inputs a reactor power equivalent signal from said pressure control apparatus, and controls a control rod drive apparatus that is connected with a control rod based on said reactor power equivalent signal. 10. The generation system according to claim 1, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control and said first and second steam control valves. 11. The generation system according to claim 10, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe so as to decrease the degree of opening of said second steam control valve installed in said inlet pipe while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve installed in said main steam pipe so that the amount of steam supplied through said inlet pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said steam control valve installed in said main steam pipe is increased. 12. The generation system according to claim 1, wherein said inlet pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater. 13. A method for controlling reactor power of a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor, and having a high-pressure turbine connected to said natural circulation reactor by a main steam pipe which introduces steam generated in said natural circulation reactor at least to said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine, a low-pressure turbine to which steam exhausted from said high-pressure turbine is supplied, a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine for at least receiving steam exhausted from said high-pressure turbine, a first steam control valve installed in said main steam pipe upstream of said high-pressure turbine at a position between the one end of the main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine, a reactor power control apparatus which controls reactor power of said natural circulation reactor, and a pressure control apparatus which controls reactor pressure in said natural circulation reactor, said moisture separation heater being connected to said main steam pipe upstream of said first steam control valve installed in said main steam pipe by an inlet steam pipe having a second steam control valve installed in said inlet steam pipe, said inlet steam pipe having one end connected to said main steam pipe and another end connected to said moisture separation heater, said second steam control valve being installed in said inlet steam pipe at a position between the one end of said inlet steam pipe connected to said main pipe and the another end of said inlet steam pipe connected to said moisture separation heater, the method comprising the steps of:controlling a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of a degree of opening of said second steam control valve installed in said inlet steam pipe based on one of a load following demand signal and a power adjustment demand signal by said pressure control apparatus; andcontrolling a control rod drive apparatus, to which a control rod is connected by said power control apparatus in order to operate said control rod when a reactor power equivalent signal is input into said power control apparatus;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 14. The method according to claim 13, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet steam pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control of said first and second steam control valves. 15. The method according to claim 14, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet steam pipe so as to decrease the degree of opening of said second steam control valve while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve so that the amount of steam supplied through said inlet steam pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said first steam control valve installed in said main steam pipe is increased. 16. The method according to claim 13, wherein said inlet steam pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater. 17. A method for controlling reactor power of a natural circulation reactor adapted to generate steam only by naturally circulating coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor, and having a high-pressure turbine connected to said natural circulation reactor by a main steam pipe adapted to at least introduce steam generated in said natural circulation reactor to said high-pressure turbine, a low-pressure turbine adapted to receive steam exhausted from said high-pressure turbine, a moisture separation heater installed between said high-pressure turbine and said low-pressure turbine adapted to at least receive steam exhausted from said high-pressure turbine, said main steam pipe having one end connected to said natural circulation reactor and another end connected to said high-pressure turbine, a first steam control valve being installed in said main steam pipe between the one end of said main steam pipe connected to said natural circulation reactor and the another end of said main steam pipe connected to said high-pressure turbine, an inlet pipe having a second steam control valve installed in said inlet pipe, said inlet pipe having one end connected to said main steam pipe at a position between the one end of said main steam pipe connected to said natural circulation reactor and said first steam control valve installed in said main steam pipe, said inlet pipe having another end connected to said moisture separation heater, said second steam control valve being installed in said inlet pipe at a position between the one end of said inlet pipe connected to said main steam pipe and the another end of said inlet pipe connected to said moisture separation heater, a control rod drive apparatus connected with a control rod adapted to be inserted and withdrawn with respect to a core of said natural circulation reactor, a power control apparatus adapted to output a power adjustment demand signal and a control rod drive command signal based on a reactor power detected by a reactor power detector adapted to detect reactor power, a control rod drive control apparatus adapted to control said control rod drive apparatus based on said control rod drive command signal, and a pressure control apparatus configured to control a pressure of said natural circulation reactor, the method comprising the steps of:controlling with said pressure control apparatus a degree of opening of said second steam control valve installed in said inlet pipe based on said power adjustment demand signal, and controlling a degree of opening of said first steam control valve installed in said main steam pipe jointly in accordance with control of the degree of the opening of said second steam control valve installed in said inlet pipe;whereby the steam is generated in said natural circulation reactor only by the natural circulation of the coolant internally within said natural circulation reactor without a pump being disposed within said natural circulation reactor. 18. The method according to claim 17, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe in inverse relation to the degree of opening of said first steam control valve installed in said main steam pipe so as to provide the joint control of said first and second steam control valves, said inlet pipe including a portion providing a direct connection between said second steam control valve and said moisture separation heater. 19. The method according to claim 18, wherein said pressure control apparatus is adapted to control the degree of opening of said second steam control valve installed in said inlet pipe so as to decrease the degree of opening of said second steam control valve installed in said inlet pipe while jointly controlling the degree of opening of said first steam control valve installed in said main steam pipe so as to increase the degree of opening of said first steam control valve installed in said main steam pipe so that the amount of steam supplied through said inlet pipe connected to said moisture separation heater is decreased and an amount of steam introduced into said high-pressure turbine through said first steam control valve installed in said main steam pipe is increased. 20. The method according to claim 17, wherein said inlet pipe includes a portion providing a direct connection between said second steam control valve and said moisture separation heater.