Patent Number: 046541861
Section: claims

1. A device for rapid and precise determination of the power of a pressurized water nuclear reactor in steady state operation and during periods of transient operation, said reactor having a core and cooling loops having a cold branch and a hot branch, said device comprising, for each cooling loop (a) means for measuring, on the one hand, the neutron power (15) and, on the other hand, the temperature of the primary fluid at a single point in said cold branch and at a single point in said hot branch;  (b) means for computing the enthalphy of the primary fluid in said cold branch and in said hot branch from said temperature measurements;  (c) a register (6) which computes an enthalpy increase (7) of said primary fluid as it flows through said core, from the difference between the enthalpy (3') in said hot branch and the enthalpy (3) in said cold branch, delayed by a time shift operator (4) expressing the average time of transit .tau.0 of a molecule of primary fluid between said two points of temperature measurement;  (d) a multiplier (8) of said increase in the enthalpy (7) by the flow rate of said primary fluid (9);  (e) a comparator (14) of a thermal power signal which is obtained (11) and of a neutron power signal which is measured (15) and made dynamically equivalent to said thermal power signal (11); and  (f) a corrector of the neutron power measurement signal (15) depending on the signal (21) produced by said comparator (14). 2. The device as claimed in claim 1, wherein said neutron power measurement signal (15) is made dynamically equivalent to said thermal power signal (11) by means of a point model (17) of heat transfer between the nuclear flux (15) and the thermal flux to said primary fluid, of a point model (18) of heat transfer of said primary fluid in the core, corresponding to the time of transit .tau..sub.i /2 of a molecule of primary fluid from the center of said core to the outlet of said core, and by means of a time shift operator (19) expressing the time of transit .tau..sub.5 of a molecule of primary fluid from the core outlet to the point of temperature measurement in said hot branch. 3. The device as claimed in claim 1 or 2, wherein the corrector (22) of said neutron power measurement signal (15) is an integrator. 4. The device as claimed in claim 1 or 2, comprising means for correcting, before its comparison to said thermal power signal (11), the neutron power measurement signal (15) for the temperature variations in the cold branch said, means comprising a correction coefficient (K.sub.1). 5. The device as claimed in claim 4, comprising means for delaying the cold branch temperature signal employed to correct said neutron power measurement signal (15), said means comprising a time shift operator expressing the time of transit .tau..sub.15 of a molecule of primary fluid between the point of temperature measurement in said cold branch and the core inlet. 6. The device as claimed in claim 5, comprising means for filtering said cold branch temperature signal to take account of the response time of said neutron power measurement signal (15) to a variation of the cold branch temperature. 7. The device according to claim 1 or 2, further comprising a device for fast and precise determination of the secondary power of said reactor, comprising for each cooling loop, in addition to said means for measuring temperature and computing the enthalpy in said cold branch and in said hot branch, imprecise but rapid means (25) for determining the thermal power produced by a steam generator associated with said reactor, a register (6') computing the reduction in the enthalpy of said primary fluid as it flows through said steam generator, from the difference between the enthalpy in said hot branch (3'), and in said cold branch (3), the enthalpy in said hot branch (3') being delayed by a time shift operator (4') expressing the time of transit .tau..sub.o of a molecule of primary fluid between the two temperature measurement points, a multiplier (8') of the decrease of enthalpy (7') by the flow rate (9) of said primary fluid, a comparator (14') of a signal (11') which is obtained at a multiplier output (8'), of the thermal power absorbed by the steam generator, to a signal (16') of the thermal power produced by said steam generator and determined by the said thermal power determining means (25), this signal (16') being made dynamically equivalent to the signal (11') of thermal power absorbed by the steam generator and a corrector (22') of the signal (16') of the thermal power produced by the steam generator depending on the signal (21') produced by said comparator (14'). 8. The device as claimed in claim 7, comprising means for making the measurement signal (16') of the thermal power produced by said steam generator dynamically equivalent to the signal (11') of thermal power absorbed by said steam generator, said means comprising a point model (17') of heat transfer between the secondary fluid and said primary fluid passing through the steam generator, of a point model (18') of heat transfer of said primary fluid in said steam generator, corresponding to the time of transit .tau..sub.10 /2 of a molecule of primary fluid from the center of said steam generator to the outlet of said steam generator and by means of a time shift operator (19') expressing the time of transit .tau..sub.11 of a molecule of primary fluid form the outlet of said steam generator to the point of measurement of the cold branch temperature. 9. The device as claimed in claim 7, wherein the corrector (22') of said measurement signal (16') of the thermal power absorbed by said steam generator is an integrator. 10. The device as claimed in claim 7, comprising means for compensating the dynamics of the measurements of the temperature of said primary fluid in said cold branch and said hot branch, said means comprising a phase lead corrector (12, 12') placed at the output of the multiplier (8, 8') of the change in enthalpy (7, 7') of the primary fluid by the flow rate (9) of the primary fluid. 11. The device as claimed in claim 7, comprising means for filtering the signal (9) of the primary flow rate before being entered into said multipliers (8, 8') in order to take account of the variation of the average time of transit .tau..sub.1 of a molecule of primary fluid passing through said core.