NEUTRON MONITORING SYSTEMS INCLUDING GAMMA THERMOMETERS AND METHODS OF CALIBRATING NUCLEAR INSTRUMENTS USING GAMMA THERMOMETERS

• US 20110064181A1
• Filed: 09/11/2009
• Published: 03/17/2011
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: Ge-Hitachi Nuclear Energy Americas LLC (GE Aerospace)
• Original Assignee: Ge-Hitachi Nuclear Energy Americas LLC (GE Aerospace)
• Inventors: Petzen, John Alexander, Moen, Stephan Craig, Foard, Adam Muhling, Meyers, Craig Glenn
• Granted Patent: US 8,238,509 B2
• Time in Patent Office: Days
• US Class Current: 376/254
• CPC Class Codes: G01T 7/005 calibration techniques stabilization of spectrometer G01T1/40
• CPC Class Codes: G21C 17/108 Measuring reactor flux
• CPC Class Codes: G21C 17/112 Measuring temperature
• CPC Class Codes: G21D 3/001 Computer implemented control
• CPC Class Codes: Y02E 30/00 Energy generation of nuclear origin
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

A method of calibrating a nuclear instrument using a gamma thermometer may include: measuring, in the instrument, local neutron flux; generating, from the instrument, a first signal proportional to the neutron flux; measuring, in the gamma thermometer, local gamma flux; generating, from the gamma thermometer, a second signal proportional to the gamma flux; compensating the second signal; and calibrating a gain of the instrument based on the compensated second signal. Compensating the second signal may include: calculating selected yield fractions for specific groups of delayed gamma sources; calculating time constants for the specific groups; calculating a third signal that corresponds to delayed local gamma flux based on the selected yield fractions and time constants; and calculating the compensated second signal by subtracting the third signal from the second signal. The specific groups may have decay time constants greater than 5×10⁻¹ seconds and less than 5×10⁵ seconds.

Claims

1. A method of calibrating a nuclear instrument using a gamma thermometer, comprising:

measuring, in the nuclear instrument, local neutron flux;

generating, from the nuclear instrument, a first signal proportional to the measured local neutron flux;

measuring, in the gamma thermometer, local gamma flux;

generating, from the gamma thermometer, a second signal proportional to the measured local gamma flux;

compensating the second signal; and

calibrating a gain of the nuclear instrument based on the compensated second signal;

wherein compensating the second signal includes;

calculating selected yield fractions for specific groups of delayed gamma sources;

calculating time constants for the specific groups of delayed gamma sources;

calculating a third signal that corresponds to delayed local gamma flux based on the selected yield fractions and time constants; and

calculating the compensated second signal by subtracting the third signal from the second signal; and

wherein the specific groups of delayed gamma sources have decay time constants greater than 5×

10<sup>−

1</sup> seconds and less than 5×

10⁵ seconds.

2. The method of claim 1, wherein the specific groups of delayed gamma sources are selected from a table or equivalent analytical representation in an American National Standards Institute/American Nuclear Society Standard for Decay Heat Power in Light Water Reactors.

3. The method of claim 2, wherein the table or equivalent analytical representation includes data related to thermal fission of Uranium-235.

4. The method of claim 2, wherein the specific groups of delayed gamma sources include thirteen specific groups of delayed gamma sources.

5. The method of claim 1, wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance,

wherein the time constants for the specific groups of delayed gamma sources are calculated in advance, or

wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance and the time constants for the specific groups of delayed gamma sources are calculated in advance.

6. The method of claim 1, wherein compensating the second signal occurs in real-time.

7. The method of claim 1, wherein calibrating the gain of the nuclear instrument based on the compensated second signal occurs automatically.

8. The method of claim 1, wherein the second signal is represented by

second signal={GT(t)/[(1,000*S₀)+(GT(t)*S₀*α

)]}

wherein the third signal is represented by

23. A neutron monitoring system, comprising:

a plurality of nuclear instruments; and

a plurality of gamma thermometers;

wherein gains of the nuclear instruments are calibrated using the gamma thermometers according to the method of claim 1.

26. A nuclear power plant, comprising the neutron monitoring system of claim 23.

9. A method of using a gamma thermometer, comprising:

measuring, in the gamma thermometer, local gamma flux;

generating, from the gamma thermometer, a first signal proportional to the measured local gamma flux;

compensating the first signal; and

calibrating a gain of a nuclear instrument based on the compensated first signal;

wherein compensating the first signal includes;

calculating selected yield fractions for specific groups of delayed gamma sources;

calculating time constants for the specific groups of delayed gamma sources;

calculating a second signal that corresponds to delayed local gamma flux based on the selected yield fractions and time constants; and

calculating the compensated first signal by subtracting the second signal from the first signal; and

wherein the specific groups of delayed gamma sources have decay time constants greater than 5×

10<sup>−

1</sup> seconds and less than 5×

10⁵ seconds.

10. The method of claim 9, wherein the specific groups of delayed gamma sources are selected from a table or equivalent analytical representation in an American National Standards Institute/American Nuclear Society Standard for Decay Heat Power in Light Water Reactors.

11. The method of claim 10, wherein the table or equivalent analytical representation includes data related to thermal fission of Uranium-235.

12. The method of claim 10, wherein the specific groups of delayed gamma sources include thirteen specific groups of delayed gamma sources.

13. The method of claim 9, wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance,

wherein the time constants for the specific groups of delayed gamma sources are calculated in advance, or

wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance and the time constants for the specific groups of delayed gamma sources are calculated in advance.

14. The method of claim 9, wherein compensating the first signal occurs in real-time.

15. The method of claim 9, wherein calibrating the gain of the nuclear instrument based on the compensated first signal occurs automatically.

24. A neutron monitoring system, comprising:

a plurality of nuclear instruments; and

a plurality of gamma thermometers;

wherein the gamma thermometers are used to calibrate gains of the nuclear instruments according to the method of claim 9.

27. A nuclear power plant, comprising the neutron monitoring system of claim 24.

16. A neutron monitoring system, comprising:

a plurality of nuclear instruments;

a plurality of gamma thermometers;

a processor; and

a memory;

wherein each gamma thermometer is associated with one of the nuclear instruments,

wherein each nuclear instrument measures local neutron flux and generates a first signal proportional to the measured local neutron flux,

wherein each gamma thermometer measures local gamma flux and generates a second signal proportional to the measured local gamma flux,

wherein selected yield fractions for specific groups of delayed gamma sources are calculated by the processor, stored in the memory, or calculated by the processor and stored in the memory,

wherein time constants for the specific groups of delayed gamma sources are calculated by the processor, stored in the memory, or calculated by the processor and stored in the memory,

wherein the processor calculates, for each gamma thermometer, a third signal that corresponds to delayed local gamma flux based on the selected yield fractions and time constants,

wherein the processor calculates a compensated second signal, for each gamma thermometer, by subtracting the third signal from the second signal,

wherein a gain of each nuclear instrument is calibrated based on the compensated second signal for the associated gamma thermometer, and

wherein the specific groups of delayed gamma sources have decay time constants greater than 5×

10<sup>−

1</sup> seconds and less than 5×

10⁵ seconds.

17. The method of claim 16, wherein the specific groups of delayed gamma sources are selected from a table or equivalent analytical representation in an American National Standards Institute/American Nuclear Society Standard for Decay Heat Power in Light Water Reactors.

18. The method of claim 17, wherein the table or equivalent analytical representation includes data related to thermal fission of Uranium-235.

19. The method of claim 17, wherein the specific groups of delayed gamma sources include thirteen specific groups of delayed gamma sources.

20. The method of claim 16, wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance,

wherein the time constants for the specific groups of delayed gamma sources are calculated in advance, or

wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance and the time constants for the specific groups of delayed gamma sources are calculated in advance.

21. The method of claim 16, wherein the processor calculates the compensated second signal for each gamma thermometer in real-time.

22. The method of claim 16, wherein the gain of each nuclear instrument is automatically calibrated based on the compensated second signal for the associated gamma thermometer.

25. A nuclear power plant, comprising the neutron monitoring system of claim 16.