Patent Number: 
Section: claims

1. An operation method of a nuclear power plant comprising the steps of:augmenting a second reactor thermal power output in a second operation cycle of a reactor larger than a first reactor thermal power output in a first operation cycle before the second operation cycle; andmaking a temperature rise amount at a high pressure feedwater heater in said second operation cycle smaller than a temperature rise amount at said high pressure feedwater heater in said first operation cycle, and making an enthalpy difference of a coolant between an inlet and outlet of said reactor in said second operation cycle larger than an enthalpy difference of said first operation cycle, wherein said nuclear power plant comprises:the reactor;a steam loop comprising a high pressure turbine and low pressure turbine where steam generated by the reactor is supplied;a condenser for condensing steam discharged from a low pressure turbine;a low pressure feedwater heater placed at a more downstream side than the condenser and at a more upstream side than a main feedwater pump, and a high pressure feedwater heater placed at a more downstream side than said main feedwater pump and at a more upstream side than said reactor; anda feedwater loop for leading feedwater discharged from the high pressure feedwater heater to said reactor. 2. An operation method of a nuclear power plant according to claim 1, wherein said first operation cycle is a first operation cycle after the installation of said nuclear plant, said second operation cycle is an operation cycle after said first operation cycle, and at least not less than one operation cycle is made to intervene between said first operation cycle and said second operation cycle.