Patent Number: 
Section: claims

1. 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. 2. A method of controlling a nuclear power plant according to  claim 1 , further comprising the steps of: claim 1 determining the first maximum linear heat generation rate and the first minimum critical power ratio by the first calculation by the core monitoring system under the state where the control signal outputted from the automatic power regulator system is held;  comparing the first maximum linear heat generation rate and the first minimum critical power ratio so determined with the predetermined thermal limit values; and  stopping the holding of the control signal in the automatic power regulator system when the first maximum linear heat generation rate and the first minimum critical power ratio are below the predetermined thermal limit values. 3. A method of controlling a nuclear power plant according to  claim 1 , further comprising the steps of: claim 1 determining the first maximum linear heat generation rate and the first minimum critical power ratio by the first calculation by the core monitoring system under the state where the control signal outputted from the automatic power regulator system is held;  comparing the first maximum linear heat generation rate and the first minimum critical power ratio so determined with the predetermined thermal limit values; and  stopping the output of the control signal in the automatic output regulator system when at least one of the first maximum linear heat generation rate and the first minimum critical power ratio exceeds the predetermined thermal limit values.