Control system of nuclear power plant, and control method thereof

A control system of a nuclear power plant comprising:

• a core monitoring system for determining a first maximum linear heat generation rate and a first minimum critical power ratio in a certain time interval by calculation;
• an automatic thermal limit monitor for determining a second maximum linear heat generation rate and a second minimum critical power ratio by a second calculation which corrects said first maximum linear heat generation rate and said first minimum critical power ratio by utilizing values of plant data at a time when said first calculation is made by said core monitoring system and said plant data of a present moment in a time interval which is shorter than the time interval of said first calculation, by said core monitoring system so as to determine said second maximum linear heat generating and said second minimum critical power ratio at the present moment, for comparing said second maximum linear heat generation rate and said second minimum critical power ratio with predetermined thermal limit values, respectively, and for outputting an operation hold instruction to an automatic power regulator system if at least one of said second maximum linear heat generation rate and said second minimum critical power ratio exceeds said predetermined thermal limit values;
• and
• said automatic power regulator system for outputting control signals to a re-circulation flow control system for controlling a re-circulation flow rate of a reactor and to a control rod control system for controlling positions of control rods, and holding said control signals in response to said operation hold instruction from said automatic thermal limit monitor.