Patent Number: 
Section: claims

1. A method of calibrating a nuclear instrument located in a nuclear reactor core, 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, using the gamma thermometer located in the nuclear reactor core, local gamma flux;generating, from the gamma thermometer, a second signal proportional to the measured local gamma flux;compensating the second signal; andcalibrating a gain of the nuclear instrument based on the compensated second signal;wherein compensating the second signal includes:filtering groups of delayed gamma sources to a reduced number of specific groups of delayed gamma sources;calculating selected yield fractions for the 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; andcalculating the compensated second signal by subtracting the third signal from the second signal; andwherein the specific groups of delayed gamma sources have decay time constants greater than 5×10−1 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 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 bysecond signal={GT(t)/[(1,000*S0)+(GT(t)*S0*α)]}wherein the third signal is represented by      third    ⁢                  ⁢    signal    =            ∑              n        =        1            13        ⁢          {                        [                                    α              n              *                        ⁢                                          GT                prompt                            ⁡                              (                t                )                                              ]                /                  [                      1            +                          (                              t                /                                  τ                  n                                            )                                ]                    }      wherein the compensated second signal is represented bycompensated second signal=second signal−third signalwherein n represents a number associated with a delayed gamma group among the specific groups of delayed gamma sources,wherein t represents time in seconds,wherein GT(t) represents a signal from a gamma thermometer in microvolts,wherein S0 represents sensitivity of the gamma thermometer in millivolts/(watt/gram),wherein α represents an alpha factor of the gamma thermometer in millivolts−1,wherein αn represents a group fraction of the delayed gamma group,wherein GTprompt(t) represents prompt gamma energy deposition in watts per gram, andwherein τn represents a time constant of the delayed gamma group. 9. A method of using a gamma thermometer in a nuclear reactor core, comprising:measuring, using the gamma thermometer located in the nuclear reactor core, local gamma flux;generating, from the gamma thermometer, a first signal proportional to the measured local gamma flux;compensating the first signal; andcalibrating a gain of a nuclear instrument based on the compensated first signal, the nuclear instrument being located in the nuclear reactor core;wherein compensating the first signal includes:filtering groups of delayed gamma sources to a reduced number of specific groups of delayed gamma sources;calculating selected yield fractions for the 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; andcalculating the compensated first signal by subtracting the second signal from the first signal; andwherein the specific groups of delayed gamma sources have decay time constants greater than 5×10−1 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 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. 16. The method of claim 1, wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance, orwherein the time constants for the specific groups of delayed gamma sources are calculated in advance. 17. The method of claim 9, wherein the selected yield fractions for the specific groups of delayed gamma sources are calculated in advance, orwherein the time constants for the specific groups of delayed gamma sources are calculated in advance. 18. The method of claim 1, wherein the nuclear instrument is a local power range monitor. 19. The method of claim 9, wherein the nuclear instrument is a local power range monitor.