Control system of nuclear power plant, and control method thereof

A method of controlling a nuclear power plant comprising the steps of:

• determining a first maximum linear heat generation rate and a first minimum critical power ratio in a certain time interval by a first calculation by a core monitoring system;
• determining a second maximum linear heat generation rate and a second minimum critical power ratio in a present moment by a second calculation by an automatic thermal limit monitor which corrects the first maximum linear heat generation rate and the first minimum critical power ratio by utilizing values of plant data at a time when the first calculation is made by the core monitoring system and the plant data of the present moment in a time interval which is shorter than the time interval of the first calculation;
• comparing the second maximum linear heat generation rate and the second minimum critical power ratio with predetermined thermal limit values, respectively;
• and
• holding a control signal outputted from an automatic power regulator system to a re-circulation flow rate control system and to a control rod positioning control system when at least one of the second maximum linear heat generation rate and the second minimum critical power ratio exceeds the predetermined thermal limit values.