Patent Number: 
Section: claims

1. 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. 2. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor compares said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system with said predetermined thermal limit values, respectively, and outputs an operation hold release instruction to said automatic power regulator system when said first maximum linear heat generation rate and said first minimum critical power ratio are below said predetermined thermal limit values, and said automatic power regulator system stops the holding operation of said control signals in response to said operation hold release instruction from said automatic thermal limit monitor. claim 1 3. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor compares said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system with said predetermined thermal limit values, respectively, after said operation hold instruction is outputted, and outputs an automatic operation exclusion instruction when at least one of said first maximum linear heat generation rate and said first minimum critical power ratio exceeds said predetermined thermal limit values, and said automatic power regulator system stops the output of said control signals when said automatic thermal limit monitor outputs said automatic operation exclusion instruction. claim 1 4. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor compares said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system with said predetermined thermal limit values, respectively, after said operation hold instruction is outputted, and outputs an operation stop instruction to said re-circulation flow control system and to said control rod control system when at least one of said first maximum linear heat generation rate and said first minimum critical power ratio is below said predetermined thermal limit values. claim 1 5. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor judges whether or not said plant data is abnormal, outputs an operation hold instruction to said automatic power regulator system when said plant data is judged as abnormal, and outputs an operation hold release instruction to said automatic power regulator system when abnormality of said plant data is thereafter restored, or when said plant data is bypassed and moreover, when said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system are below said predetermined thermal limit values. claim 1 6. A control system of a nuclear power plant according to  claim 2 , wherein said automatic thermal limit monitor judges whether or not said plant data is abnormal, outputs an operation hold instruction to said automatic power regulator system when said plant data is judged as abnormal, and outputs an operation hold release instruction to said automatic power regulator system when abnormality of said plant data is thereafter restored, or when said plant data is bypassed and moreover, when said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system are below said predetermined thermal limit values. claim 2 7. A control system of a nuclear power plant according to  claim 3 , wherein said automatic thermal limit monitor judges whether or not said plant data is abnormal, outputs an operation hold instruction to said automatic power regulator system when said plant data is judged as abnormal, and outputs an operation hold release instruction to said automatic power regulator system when abnormality of said plant data is thereafter restored, or when said plant data is bypassed and moreover, when said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system are below said predetermined thermal limit values. claim 3 8. A control system of a nuclear power plant according to  claim 4 , wherein said automatic thermal limit monitor judges whether or not said plant data is abnormal, outputs an operation hold instruction to said automatic power regulator system when said plant data is judged as abnormal, and outputs an operation hold release instruction to said automatic power regulator system when abnormality of said plant data is thereafter restored, or when said plant data is bypassed and moreover, when said first maximum linear heat generation rate and said first minimum critical power ratio determined by said core monitoring system are below said predetermined thermal limit values. claim 4 9. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor outputs a signal requesting the calculation of said first maximum linear heat generation rate and said first minimum critical power ratio to said core monitoring system when it outputs said operation hold instruction to said automatic power regulator system. claim 1 10. A control system of a nuclear power plant according to  claim 1 , wherein said automatic thermal limit monitor determines said second maximum linear heat generation rate and said second minimum critical power ratio by utilizing said first maximum linear heat generation rate and said first minimum critical power ratio determined afresh by said core monitoring system. claim 1 11. A control system of a nuclear power plant according to  claim 1 , wherein said second maximum linear heat generation rate and said second minimum critical power ratio are equal in values to said first maximum linear heat generation rate and said first minimum critical power ratio when said core monitoring system determines said first maximum linear heat generation rate and said first minimum critical power ratio. claim 1 12. A control system of a nuclear power plant according to  claim 1 , wherein said second calculation is effected in a time interval no greater than about 10 seconds. claim 1 13. A control system of a nuclear power plant according to  claim 12 , wherein said second calculation is effected in a time interval of no greater than about 1 second. claim 12