Patent Number: 040452824
Section: claims

1. A method of thermal monitoring of a nuclear reactor core having fuel assemblies at temperatures T.sub.1 and T.sub.2 utilizing coolant temperatures detected at the outlets of a plurality of said fuel assemblies comprising the steps of establishing at each instant the mean core outlet temperature by forming the half-sum of the mean T.sub.1 and T.sub.2 core outlet temperatures corresponding respectively to the mean value of the coolant temperatures at the outlet of at least part of the fuel assemblies at temperatures T.sub.1 and to the mean value of the coolant temperatures at the outlet of at least part of the fueld assemblies at temperatures T.sub.2 and the difference between said core outlet temperatures T.sub.1 and T.sub.2,  producing for each fuel assembly an analog signal corresponding to the temperature difference between the coolant temperature at the outlet of said fuel assembly and the mean core outlet temperature as initially increased or decreased by a predetermined fraction of the difference between the mean core outlet temperatures T.sub.1 and T.sub.2 to define a state of equilibrium at which said temperature difference is equal to zero, and  processing said signal to initiate appropriate safety actions by overstepping of threshold values corresponding to temperature variations permitted on each side of the equilibrium zero.  N thermocouples which are equal in number to the number N of reactor core fuel assemblies at temperatures T.sub.1 and T.sub.2 ,  N measuring channels connected individually to each of the N thermocouples and each comprising in series: 2. A method according to claim 1, wherein said analog signal representing said temperature difference is generated for each fuel assembly aforesaid by forming the sum of three signals representing respectively the temperature of the coolant at the outlet of said fuel assembly, a value of opposite sign value of said mean core outlet temperature and the fraction of said difference between the mean core outlet temperatures T.sub.1 and T.sub.2 corresponding to the position of said fuel assembly. 3. An electric device for the thermal monitoring of a nuclear reactor core comprising 4. An electronic device for the thermal monitoring of a nuclear reactor core according to claim 3, wherein said associated analog circuits comprise in common two operational amplifiers for delivering respectively a signal corresponding to the mean core outlet temperature T.sub.1 and to the mean core outlet temperature T.sub.2, these two amplifiers being each placed at the output of a plurality of said amplifiers for the signals detected by the thermocouples selected as a function of the nature of the mean value to be established. 5. A device for the thermal monitoring of a nuclear reactor core according to claim 4, wherein the associated analog circuit for delivering the characteristic fraction of each fuel assembly of the difference between the mean core outlet temperatures T.sub.1 and T.sub.2 has successively at the output of said mean temperature T.sub.1 amplifier and at the output of an inverting amplifier which is in turn placed at the output of said mean temperature T.sub.2 amplifier, a summing amplifier and a series of amplifiers having symmetrical outputs between which are connected N potentiometers for adjusting said difference between the mean core outlet temperatures T.sub.1 and T.sub.2. 6. An electronic device for the thermal monitoring of a reactor core according to claim 4, wherein said associated analog circuit for delivering the value of opposite sign value of the mean core outlet temperature comprises at the output of said T.sub.1 and T.sub.2 core outlet temperature a summing amplifier having a gain of 2:1 and an inverting amplifier.