Patent Number: 
Section: claims

1. A method for measuring a neutron flux in a core of a nuclear reactor, the method comprising several steps recurrently performed at instants separated by a period, the method comprising at each given instant the following steps:acquiring a total signal by a cobalt neutron detector placed inside the core of the reactor;assessing a calibration factor representative of a delayed component of the total signal due to a presence of cobalt 60 in the cobalt neutron detector;assessing a corrected signal representative of the neutron flux at the cobalt neutron detector from the total signal and from the calibration factor;assessing a slope representative of a time-dependent change in the calibration factor between a preceding instant and a given instant;wherein the calibration factor at the given instant is being assessed as a function of the calibration factor assessed at the preceding instant, of the slope, and of the period separating the given instant from the preceding instant. 2. The measurement method according to claim 1, wherein the neutron detector is a fixed detector. 3. The measurement method according to claim 1, wherein the slope at the given instant is assessed at least as a function of the corrected signal at the preceding instant and of the calibration factor at the preceding instant. 4. The measurement method according to claim 3, wherein at each given instant the measurement method comprises a step for assessing a load factor representative of the time-dependent change in a power of the reactor locally around the neutron detector between the preceding instant and the given instant, the slope at the given instant being assessed also as a function of the load factor. 5. The measurement method according to claim 4, wherein the load factor at each given instant is assessed by calculating an average power of the reactor locally around the neutron detector between the preceding instant and the given instant, and by dividing the average power by the value of the power of the reactor locally around the neutron detector at the preceding instant. 6. The measurement method according to claim 3, wherein at each given instant the measurement method comprises a step for assessing a load factor representative of a time-dependent change in a power of the reactor between the preceding instant and the given instant, the slope at the given instant also being assessed as a function of the load factor. 7. A device for measuring a neutron flux in a core of a nuclear reactor, the measurement device comprising at least one cobalt neutron detector placed inside the core of the reactor and a computer;the computer having an acquiring device for recurrently acquiring at given instants separated by a period, a total signal by the neutron detector;the computer having a calibration assessor for assessing at each given instant a calibration factor representative of a delayed component of the total signal due to the presence of cobalt 60 in the neutron detector;the computer having a signal assessor for assessing at each given instant a corrected signal representative of the neutron flux at the neutron detector from the total signal and from the calibration factor;the computer having a slope assessor for assessing at each given instant a slope representative of the time-dependent change in the calibration factor between the preceding instant and the given instant;the calibration assessor for assessing the calibration factor being capable of assessing the calibration factor at the given instant as a function of the calibration factor assessed at a preceding instant of the slope, and of the period separating the given instant from the preceding instant. 8. The measurement device according to claim 7, wherein the neutron detector is a fixed detector. 9. The measurement device according to claim 7, wherein the slope assessor is capable of assessing the slope at the given instant at least as a function of the corrected signal at the preceding instant and of the calibration factor at the preceding instant. 10. The measurement device according to claim 9, further comprising a load factor assessor for assessing at each given instant a load factor representative of the time-dependent change in a power of the reactor locally around the detector between the preceding instant and the given instant, the slope assessor device being capable of assessing the slope at the given instant also as a function of the load factor. 11. The measurement device according to claim 10, the load factor assessor being capable of assessing the load factor at each given instant by calculating an average power of the reactor locally around the neutron detector between the preceding instant and the given instant, and by dividing the average power by a value of the power of the reactor locally around the neutron detector at the preceding instant. 12. The measurement device according to claim 7, wherein the acquiring device is an amplification and digitizing device.