Patent ID: 7614233

Claim:
An operation method of a nuclear power plant comprising: a nuclear reactor; a high pressure steam system supplied with steam generated in said nuclear reactor and extending from an outlet of said nuclear reactor to an inlet of a low pressure turbine via a high pressure turbine; a low pressure steam system extending from the inlet of said low pressure turbine to an inlet of a condenser for condensing the steam discharged from said low pressure turbine; and a feedwater system including a feedwater heater for heating feedwater supplied from said condenser and introducing the feedwater discharged from said feedwater heater to said nuclear reactor, the operation method comprising the steps of: uprating second nuclear thermal power in a second operation cycle of said nuclear reactor from first nuclear thermal power in a first operation cycle before the second operation cycle; and reducing a proportion of a mass flow rate of steam extracted from said high pressure steam system and introduced to said feedwater heater in the second operation cycle with respect to a mass flow rate of main steam at the outlet of said nuclear reactor in comparison with a proportion of a mass flow rate of steam extracted from said high pressure steam system and introduced to said feedwater heater in the first operation cycle with respect to the mass flow rate of main steam at the outlet of said nuclear reactor, such that temperature of the feedwater discharged from said feedwater heater lowers in the range of 1° C. to 40° C. in the second operation cycle from the feedwater temperature in the first operation cycle.