Patent ID: 8238509

Claim:
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; and calibrating 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; 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 −1 seconds and less than 5×10 5 seconds.