Nuclear power plant control method and system

Abstract

The control method executes an instruction following mode in which the nuclear power plant is controlled in accordance with a power operation instruction (COP) when an imbalance between the primary output signal (S1) and the secondary output signal (S2) is not detected, and automatically executes a power limiting mode in which a target balanced output (PEC) that is less than or equal to the primary output (P1) and less than or equal to the secondary output (P2) is calculated, and the nuclear power plant (2) is controlled in accordance with the target balanced output (PEC) when an imbalance is detected.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a nuclear power plant. [Background technology]

[0002] A nuclear power plant has independent primary and secondary water circuits, a nuclear reactor that heats the water circulating in the primary circuit, one or more steam generators that thermally couple the primary and secondary circuits and transfer heat from the primary to the secondary circuit to produce steam in the secondary circuit, and a steam turbine installed in the secondary circuit that generates mechanical energy from the steam, which is converted to electrical energy using a generator coupled to the steam turbine. Summary of the Invention [Problem to be solved by the invention]

[0003] One object of the present invention is to propose a method for controlling a nuclear power plant that is capable of maintaining the nuclear power plant in a suitable operating range and that is preferably usable over a wide range of reactor power outputs. [Means for solving the problem]

[0004] In order to achieve the above object, the present invention provides a control method implemented by an automatic control system for controlling a pressurized water nuclear power plant including a nuclear reactor, a primary circuit for circulating water, a secondary circuit for circulating water, and N steam generators (N is an integer of 1 or more), wherein each steam generator is configured to transfer thermal energy from the primary circuit to the secondary circuit accompanied by generation of steam in the secondary circuit; calculating a primary power output representing the thermal power generated by the nuclear reactor and a secondary power output representing the thermal power transferred by the steam generator from the primary circuit to the secondary circuit; detecting a possible imbalance between the primary output and / or a primary output signal calculated depending on at least one variable indicative of a variation of the primary output, and the secondary output and / or a secondary output signal calculated depending on at least one variable indicative of a variation of the secondary output; If no imbalance is detected, implementing a command follow mode in which the nuclear power plant is controlled in response to a power operation command received by a control system so that the primary output and the secondary output follow the power operation command; and automatically executing a power limiting mode when an imbalance is detected, the power limiting mode including calculating a target balanced power output by the control system that is less than or equal to the primary power output and less than or equal to the secondary power output, and controlling the nuclear power plant in accordance with the target balanced power output.

[0005] According to a particular embodiment, the control method comprises one or more of any of the following functions, individually or in any technically possible combination: The secondary power output is determined by calculating the thermal power transferred from the primary circuit to the secondary circuit by each steam generator and calculating the sum of these thermal power outputs. The primary output signal is calculated in response to the primary output, a filtered derivative of the primary output, an axial offset of the reactor, a filtered derivative of the axial offset of the reactor, a control cluster motion signal and / or a filtered derivative of a control cluster motion signal. The primary output signal is calculated as the sum of the primary output and one or more of a filtered derivative of the primary output multiplied by a primary output coefficient, an absolute value of a filtered derivative of an axial offset multiplied by an axial offset coefficient, and a filtered derivative of a control cluster motion signal multiplied by a motion signal coefficient. The secondary output signal is calculated in response to the secondary output, a steam pressure representing the steam pressure at the outlet of the steam generator, a filtered derivative of the steam pressure, a feedwater temperature representing the water temperature at the inlet of the steam generator, a filtered derivative of the feedwater temperature, a feedwater flow rate representing the water flow rate at the inlet of the steam generator, and / or a filtered derivative of the feedwater flow rate. The secondary output signal is calculated as the sum of the secondary output and one or more of a filtered derivative of steam pressure multiplied by a steam pressure coefficient, a filtered derivative of feedwater temperature multiplied by a feedwater temperature coefficient, and a filtered derivative of feedwater flow rate multiplied by a feedwater flow rate coefficient. The step of detecting the possible imbalance includes comparing a difference between the primary output signal and the secondary output signal to a lower threshold and / or an upper threshold. The step of detecting the imbalance includes generating a logic signal requesting rebalancing and commanding a switch to the power limiting mode when the difference is less than the lower threshold and / or greater than the upper threshold. The power limiting mode is enabled for the power limiting duration determined in the step of detecting the imbalance. The target balanced output is calculated according to the maximum balanced output, and the target balanced output is equal to or less than the maximum balanced output. The maximum balanced output is calculated as a function of the primary output minus any non-zero deviation. The primary output minus the non-zero deviation is filtered so that the absolute value of its derivative remains below a predetermined derivative threshold. The control method includes clipping the maximum balanced output to be less than a predetermined maximum value and / or greater than a predetermined minimum value. The target balanced power output is determined as the minimum of the primary power output, the secondary power output, and the maximum balanced power output. The control method includes, in the output limit mode, calculating a primary output command and a secondary output command according to the target balanced output, and controlling the nuclear power plant so that the primary output matches the primary output command and the secondary output matches the secondary output command. In the power limiting mode, the primary power command is calculated as equal to the target balanced power and optionally filtered, preferably by a low pass filter, and the secondary power command is calculated as equal to the target balanced power and optionally filtered, preferably by a low pass filter.

[0006] The present invention also relates to a nuclear power plant control system configured to carry out the above-described control method.

[0007] The present invention also relates to a nuclear power plant comprising a primary circuit for the circulation of water incorporating a nuclear reactor, a secondary circuit for the circulation of water, and N steam generators (N being an integer equal to or greater than 1), including a control system as described above, each steam generator being configured to transfer thermal energy from the primary circuit to the secondary circuit accompanied by the generation of steam in the secondary circuit.

[0008] The invention also relates to a computer program product recordable on a computer medium or in a computer memory and executable by a processor, the computer program product comprising software code instructions for carrying out the control method described above.

[0009] The invention and its advantages will be better understood on reading the following non-limiting, illustrative description made with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0010] [Figure 1] Schematic diagram of a nuclear power plant showing the primary and secondary circuits incorporating the reactor. [Figure 2] FIG. 2 is a block diagram illustrating a control method for the nuclear power plant shown in FIG. 1. [Figure 3] FIG. 2 is a block diagram illustrating a control method for the nuclear power plant shown in FIG. 1. [Figure 4] FIG. 2 is a block diagram illustrating a control method for the nuclear power plant shown in FIG. 1. [Figure 5]FIG. 2 is a block diagram illustrating a control method for the nuclear power plant shown in FIG. 1. [Figure 6] FIG. 2 is a block diagram illustrating a control method for the nuclear power plant shown in FIG. 1. [Figure 7] 1 is a schematic diagram of a nuclear power plant according to another embodiment. [Figure 8] 2 is a schematic diagram of a nuclear power plant in yet another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The nuclear power plant 2 shown in FIG. 1 includes a primary circuit 4 for circulating water and a secondary circuit 6 for circulating water, and the primary circuit 4 and the secondary circuit 6 are thermally coupled separately via N steam generators 8 (N is an integer equal to or greater than 1).

[0012] Each steam generator 8 is disposed between the primary circuit 4 and the secondary circuit 6 and is configured to exchange heat between the water in the primary circuit 4 and the water in the secondary circuit 6 .

[0013] In operation, each steam generator 8 generates steam for the secondary circuit 6. In the secondary circuit 6, each steam generator 8 provides water in a liquid state at its inlet and water in a gaseous state, i.e., steam, at its outlet.

[0014] The primary circuit 4 includes a nuclear reactor 10 for heating water circulating through the primary circuit 4 .

[0015] The nuclear power plant 2 may be, for example, a pressurized water nuclear power plant, in which case the reactor 10 is a pressurized water reactor (PWR), or a boiling water nuclear power plant, in which case the reactor 10 is a boiling water reactor (BWR).

[0016] The primary circuit 4 includes, for example, N fluid primary loops 12 , each primary loop 12 fluidly connecting the reactor 10 with each steam generator 8 .

[0017] 1 shows a single steam generator 8 and a single primary loop 12. Alternatively, the primary circuit 4 may include multiple primary loops 12, for example, four primary loops 12.

[0018] Nuclear reactor 10 includes a reactor vessel 14. Each primary loop 12 connects reactor vessel 14 to a respective steam generator 8. Each primary loop 12 is connected to reactor vessel 14 by an inlet pipe 14A and an outlet pipe 14B.

[0019] The nuclear reactor 10 includes a core 16 formed by a plurality of nuclear fuel assemblies 18 arranged side by side within a reactor vessel 14 .

[0020] The reactor 10 includes a control cluster 20 that can be lowered into and raised from the core 16 to control the reactivity of the reactor 10 .

[0021] The control clusters 20 include, for example, control clusters that can be selectively inserted into the core 16 to reduce reactivity or extracted from the core 16 to increase reactivity, and shutdown clusters that can be released into the core 16 to cause an automatic shutdown of the reactor 10.

[0022] Each primary loop 12 includes a primary pump 22 for forcibly circulating water within the primary loop 12 .

[0023] If the nuclear power plant 2 is a pressurized water nuclear power plant, the primary circuit 4 includes a pressurizer 24 configured to maintain sufficient pressure within the primary circuit 4 to maintain the water circulating within the primary circuit 4 in a liquid state.

[0024] The pressurizer 24 is fluidly connected to the hot branch of the primary loop 12 , i.e., the branch through which fluid flows from the reactor 10 to the steam generator 8 on the primary loop 12 .

[0025] If the primary circuit 4 includes multiple primary loops 12 , the primary circuit 4 may include, for example, a single pressurizer 24 connected to the hot branch of one of the primary loops 12 .

[0026] The secondary circuit 6 includes, for example, a single secondary loop 26 supplied with steam from the steam generator 8 of each primary loop 12 .

[0027] Alternatively, the secondary circuit 6 may include a secondary loop 26 corresponding to each primary loop 12 , with steam supplied from the steam generator 8 of that primary loop 12 .

[0028] The secondary circuit 6 includes one or more turbines 28, each configured to convert thermal energy contained in the steam circulating through the secondary circuit 6 into mechanical energy.

[0029] The secondary circuit 6 includes one or more secondary pumps 30 for forcibly circulating water within the secondary circuit 6 .

[0030] The secondary circuit 6 includes one or more condensers 32, each positioned downstream of a turbine 28, for cooling the steam exiting the turbine 28 back to a liquid state.

[0031] Each condenser 32 is disposed, for example, on the secondary circuit 6 and is configured to exchange heat between the water in the secondary circuit 6 and the water circulating in the cooling circuit 34 .

[0032] The nuclear power plant 2 includes one or more generators 36, each mechanically coupled to a turbine 28 to generate electrical energy from the mechanical energy generated by the turbine 28. Each generator 36 is mechanically coupled to a turbine 28 to generate electrical energy from the mechanical energy generated by the turbine 28. The electrical energy is provided, for example, to an electrical grid.

[0033] The nuclear power plant 2 comprises a control system 40 configured to automatically control the nuclear power plant 2 and in particular to execute a method for controlling the nuclear power plant 2 .

[0034] The control system 40 comprises a first sensor for measuring a first operating parameter of the nuclear power plant 2 related to the operation of the primary circuit 4 and a second sensor for measuring a second operating parameter of the nuclear power plant 2 related to the operation of the secondary circuit 6.

[0035] The first sensor includes, for example, a neutron detector 42 for measuring the neutron flux within the reactor 10 .

[0036] The neutron detectors 42 include internal neutron detectors located inside the reactor core 16 (commonly referred to as "in-core" detectors) and / or external neutron detectors (not shown) located outside the reactor vessel 14 of the reactor 10 in which the reactor core 16 is contained (commonly referred to as "ex-core" detectors).

[0037] For example, the neutron detector 42 is a self-powered neutron detector (also called SPND, an acronym for "Self-Powered Neutron Detector").

[0038] Neutron detector 42 is, for example, a cobalt, vanadium and / or rhodium detector.

[0039] By measuring the neutron flux generated in the reactor 10 at a certain time, a value representing the instantaneous thermal power generated in the reactor 10 (hereinafter referred to as "primary power") can be calculated.

[0040] The second sensor may include, for example, for each steam generator 8, an outlet pressure sensor 44 for measuring the pressure in the secondary circuit 6 at the outlet of the steam generator 8, a steam flow sensor 45 for measuring the steam flow rate in the secondary circuit 6 at the outlet of the steam generator 8, an inflow water flow sensor 46 for measuring the flow rate of water flowing from the steam generator 8 into the secondary circuit 6, and / or an inflow water temperature sensor 48 for measuring the temperature of water flowing from the steam generator 8 into the secondary circuit 6.

[0041] By directly or indirectly measuring the pressure of the steam leaving the steam generator 8, the flow rate of the steam leaving the steam generator 8, the flow rate of the water entering the steam generator 8, and / or the temperature of the water entering the steam generator 8 at a given moment, it is possible to calculate a value representing the instantaneous heat power transferred by the steam generator 8 from the primary circuit 4 to the secondary circuit 6.

[0042] The control system 40 includes an electronic control unit 50 configured to control and operate the nuclear power plant 2 by executing a control command methodology.

[0043] The electronic control unit 50 is configured to receive the first and second operating parameters, for example, by receiving measurement signals provided by the first and second sensors.

[0044] The electronic control unit 50 is, for example, configured to control the primary circuit 4 and the secondary circuit 6 in response to first and second parameters.

[0045] The electronic control unit 50 is configured, for example, to control the control cluster 20 to regulate the reactivity of the reactor, and / or to control each primary pump 22 to regulate the flow of water in the primary circuit 4, and / or to control each secondary pump 30 to regulate the flow of water in the secondary circuit 6, and to control each turbine 28 and / or each generator 36.

[0046] As shown in Figure 2, the control method is as follows: Calculating a primary power P1 representing the thermal power generated by the nuclear reactor 10 and a secondary power P2 representing the thermal power transferred by the steam generator 8 from the primary circuit 4 to the secondary circuit 6; detecting a possible imbalance between the primary output P1 and / or a primary output signal S1 calculated according to at least one variable indicative of fluctuations in the primary output P1, and the secondary output P2 and / or a secondary output signal S2 calculated according to at least one variable indicative of fluctuations in the secondary output P2; If no imbalance is detected, executing a command following mode in which the nuclear power plant 10 is controlled in accordance with a power operation command COP received by a control system so that the primary output P1 and the secondary output P2 follow the power operation command COP; When an imbalance is detected, the control system 40 calculates a target balanced output PEC that is equal to or less than the primary output P1 and the secondary output P2, and controls the nuclear power plant 2 in accordance with the target balanced output PEC, automatically executing an output limiting mode.

[0047] The primary power P1 is calculated, for example, in response to a measurement of a first operating parameter of the nuclear power plant 2 measured by a first sensor related to the operation of the primary circuit 4, in particular in response to a measurement of the neutron flux in the core 16 of the nuclear reactor 10.

[0048] The measurement of the first parameter is performed by a first sensor, such as a neutron detector 42 mounted on the reactor 10 .

[0049] The secondary power output P2 is calculated as a function of a second operating parameter of the nuclear power plant 2, which is for example related to the operation of the secondary circuit 6 and measured by a second sensor.

[0050] The secondary power output P2 is calculated, for example, by determining the thermal power transferred from the primary circuit 4 to the secondary circuit 6 by each steam generator 8 and calculating the secondary power output P2 as the sum of the transferred power outputs.

[0051] For each steam generator 8, the power transmitted from the primary circuit 4 to the secondary circuit 6 is calculated in a known manner, for example as a function of second parameters, in particular the steam pressure leaving the steam generator 8 in the secondary circuit 6, the steam flow rate leaving the steam generator 8 in the secondary circuit 6, the water flow rate entering the steam generator 8 in the secondary circuit 6, and / or the temperature of the water entering the steam generator 8 in the secondary circuit 6.

[0052] Measurements of the second parameter are provided, for example, by outlet pressure sensor 44, steam flow sensor 45, inlet water flow sensor 46, and / or inlet water temperature sensor 48, respectively.

[0053] In another embodiment, the second parameter is measured by an outlet pressure sensor 44, a steam chimney pressure sensor (not shown) positioned to measure the pressure of steam in the steam chimney of the secondary circuit, an inflow water flow sensor 46, and an inflow water temperature sensor 48, respectively.

[0054] In a secondary circuit 6 having multiple steam generators 8 feeding the same turbine 28 , the steam drum is a collector that receives the steam produced by the steam generators 8 and supplies it to the turbine 28 .

[0055] As shown in FIG. 3, the electronic control device 50 includes, for example, a primary power calculation module 52 that calculates the primary power P1 generated in the reactor 10, and a secondary power calculation module 54 that calculates the secondary power P2 transmitted from the primary circuit 4 to the secondary circuit 6.

[0056] The primary power calculation module 52 receives measurement signals provided, for example, by the neutron detector 42, and the secondary power calculation module 54 receives measurement signals provided, for example, by an outlet pressure sensor 44 measuring the pressure in the secondary circuit 6 at the outlet of the steam generator 8, a steam flow sensor 45 measuring the flow rate of steam in the secondary circuit 6 at the outlet of the steam generator 8, an inflow water flow sensor 46 measuring the flow rate of liquid water flowing into the steam generator 8 in the secondary circuit 6, and / or an inflow water temperature sensor 48 measuring the temperature of water at the inlet of the steam generator 8 in the secondary circuit 6.

[0057] The electronic control unit 50 is configured to include, for example, a control module 56 that receives a power operation instruction COP, a calculated primary power output P1, and a calculated secondary power output P2, and to generate instructions for the functional units of the nuclear power plant 2 and control the nuclear power plant 2.

[0058] The control module 56 is configured to generate control commands for the control clusters 20 of, for example, each primary pump 22 , each turbine 28 , each secondary pump 30 and / or each generator 36 .

[0059] In the command following mode, the balance between the primary output P1 and the secondary output P2 is maintained as a rule, and the nuclear power plant 2 is controlled so that the primary output P1 and the secondary output P2 are each maintained approximately equal to the power operation command COP received by the control system 40.

[0060] The power operation command COP is provided by, for example, an operator who operates the nuclear power plant 2.

[0061] The power operating instructions COP may optionally be changed and / or modulated in response to operating parameters of the power grid to which the nuclear power plant 2 is connected, for example in response to fluctuations in the frequency of the power grid.

[0062] During operation of the nuclear power plant 2, an imbalance may occur between the primary power output P1 and the secondary power output P2.

[0063] If the secondary power P2 is less than the primary power P1, power may accumulate in the primary circuit 4, which is undesirable.

[0064] Conversely, if the secondary power P2 is greater than the primary power P1, this may lead to cooling of the core 16, which is undesirable.

[0065] The power limiting mode is designed to re-establish balance between the primary power output P1 and the secondary power output P2 while maintaining the nuclear power plant 2 within its normal operating region, avoiding the intervention of protection systems that may be automatically activated and shut down the nuclear power plant 2 if the nuclear power plant 2 were to move outside of its normal operating region.

[0066] In the power limiting mode, a target balanced power output PEC is calculated by the control system 40, preferably independently of the power operating command COP, and the nuclear power plant 2 is then controlled according to the target balanced power output PEC and not according to the power operating command COP.

[0067] The target balanced output PEC is calculated to be less than or equal to the primary output P1 and less than or equal to the secondary output P2, and the output limiting mode causes a decrease in the primary output P1 and / or a decrease in the secondary output P2 to balance them.

[0068] The power limiting mode is designed to be implemented automatically using the control system 40 while remaining within the normal operating range of the nuclear power plant 2, and therefore can be implemented without the intervention of the protection system.

[0069] As mentioned above, the imbalance is detected by comparing the primary output signal S1 and the secondary output signal S2.

[0070] The primary output signal S1 is calculated to represent the primary output P1, and optionally indicates changes in the primary output P1.

[0071] A secondary output signal S2 is calculated to represent the secondary output P2, and optionally indicates changes in the secondary output P2.

[0072] By considering changes in the primary output P1 and / or secondary output P2, the imbalance can be predicted.

[0073] In one embodiment, as shown in FIG. 4 , the primary output signal S1 is calculated as a function of, for example, the primary output P1, a filtered derivative of the primary output, the axial offset AO of the reactor 10, the absolute value of the filtered derivative of the axial offset AO of the reactor 10, the motion signal PG indicating the motion of the control cluster 20 and / or the filtered derivative of the motion signal PG of the control cluster 20.

[0074] A "filtered" derivative is a derivative combined with a filter that cuts out high frequency fluctuations and passes low frequency fluctuations (a low pass filter).

[0075] By considering the derivative of a quantity, one can take into account variations in that quantity and predict changes.

[0076] The low-pass filter applied to the derivative makes it possible to smooth the derivative so as to take into account only the trends in the magnitude fluctuations shown by the derivative, and not excessively sharp fluctuations that do not represent the actual trends in the evolution of the signal.

[0077] In a known manner, the axial offset AO of the reactor 10 represents an uneven distribution of neutron flux along the reactor 10 assembly, in particular an imbalance of neutron flux between the bottom of the reactor 10 and the top of the reactor 10.

[0078] The axial offset AO can be determined, for example, using a set of neutron detectors 42 mounted on the reactor 10 and distributed vertically so as to measure differences in neutron flux as a function of position along the reactor 10.

[0079] Variations in the axial offset AO may indicate future variations in the primary output P1. By considering the axial offset AO, and in particular the absolute value of the filtered derivative of the axial offset AO, it is possible to predict variations in the primary output P1.

[0080] Movement of the control cluster 20 can lead to fluctuations in the primary output P1. By considering the movement signal PG, and in particular the filtered derivative of the movement signal PG, it is possible to predict the fluctuations in the primary output P1 due to movement of the control cluster 20.

[0081] In one embodiment, the primary output signal S1 is calculated to be equal to the primary output signal P1.

[0082] Also preferably, the primary output signal S1 is calculated as the sum of the primary output P1 and one or more of a filtered derivative of the primary output P1 multiplied by a primary output coefficient KP1, an absolute value of a filtered derivative of the axial offset AO of the reactor 10 multiplied by an axial offset coefficient KAO, and a filtered derivative PG of the control cluster motion signal multiplied by a cluster motion coefficient KPG.

[0083] Each of the above coefficients (primary power coefficient KP1, axial offset coefficient KAO, cluster motion coefficient KPG) is preferably positive or zero.

[0084] Each of the above coefficients (primary power coefficient KP1, axial offset coefficient KAO, cluster motion coefficient KPG) has its own unique value. Each coefficient can have a different value. In very special cases, they can even be equal.

[0085] These coefficients are used to adjust the response of the control method depending on the quantity of interest.

[0086] In the example shown in FIG. 4, the primary output signal S1 is calculated as the sum of the primary power P1, the filtered derivative of the primary power P1 multiplied by a primary power coefficient KP1, the absolute value of the filtered derivative of the axial offset AO of the reactor 10 multiplied by an axial offset coefficient KAO, and the filtered derivative of the control cluster motion signal PG multiplied by a cluster motion coefficient KPG.

[0087] The secondary signal S2 is calculated in response to the secondary output P2, a steam pressure PV representing the steam pressure at the outlet of the steam generator 8, a filtered derivative of the steam pressure PV, a feedwater temperature TE representing the water temperature at the inlet of the steam generator 8, a filtered derivative of the feedwater temperature TE, a feedwater flow rate DE representing the water flow rate at the inlet of the steam generator 8, and / or a filtered derivative of the feedwater flow rate DE.

[0088] If the nuclear power plant 2 includes multiple steam generators 8, the steam pressure PV is preferably determined as the average of the steam pressures at the outlets of the steam generators 8, determined using, for example, steam pressure sensors 44.

[0089] Alternatively, if the nuclear power plant 2 includes a single steam generator 8, the steam pressure PV is determined to be equal to the steam pressure PV at the outlet of the steam generator 8 of the nuclear power plant 2.

[0090] If the nuclear power plant 2 includes multiple steam generators 8, the feedwater temperature TE is preferably determined as the average of the feedwater temperatures at the inlets of the steam generators 8, determined using, for example, water temperature sensors 46.

[0091] Alternatively, if the nuclear power plant 2 includes a single steam generator 8 , the feedwater temperature TE is determined to be equal to the feedwater temperature at the inlet of the steam generator 8 of the nuclear power plant 2 .

[0092] If the nuclear power plant 2 includes multiple steam generators 8, the inflow water flow rate DE is preferably determined as the average value of the water flow rates at the inlets of the steam generators 8, determined for example using a water flow sensor 48.

[0093] Alternatively, if the nuclear power plant 2 includes a single steam generator 8 , the influent water flow rate DE is determined to be equal to the water flow rate at the inlet of the steam generator 8 of the nuclear power plant 2 .

[0094] By taking into account the steam pressure PV, the feedwater temperature TE and / or the feedwater flow rate DE, and in particular the filtered derivatives of one or more of these parameters, it is possible to predict the variations in the secondary power output P2.

[0095] In one embodiment, the secondary output signal S2 is calculated as the sum of the secondary output P2 and one or more of a filtered derivative of the steam pressure PV multiplied by a steam pressure coefficient KPV, which is preferably negative or zero, a filtered derivative of the feedwater temperature TE multiplied by a water temperature coefficient KTE, which is preferably negative or zero, and a filtered derivative of the feedwater flow rate DE multiplied by a feedwater flow rate coefficient KDE, which is preferably positive or zero.

[0096] As shown in FIG. 4, the secondary output signal S2 is calculated as the sum of the secondary output P2, a filtered derivative of the steam pressure PV multiplied by a steam pressure coefficient KPV, a filtered derivative of the feedwater temperature TE multiplied by a water temperature coefficient KTE, and a filtered derivative of the feedwater flow rate DE multiplied by a feedwater flow rate coefficient KDE.

[0097] The low-pass filters used to calculate the different filtered derivatives used to calculate the primary output signal S1 and the secondary output signal S2 may be the same. Alternatively, they may not all be the same. In this case, at least two of these low-pass filters are different. In certain instances, they are all different.

[0098] As shown in FIG. 4, the electronic control unit 50 includes a detection module 62 configured to detect the imbalance by determining and comparing the primary output signal S1 and the secondary output signal S2.

[0099] The detection module 62 includes a primary signal module 64 and a secondary signal module 66 for calculating a primary output signal S1 and a secondary output signal S2, respectively.

[0100] The primary signal module 64 and the secondary signal module 66 each include one or more derivative modules 68 configured to receive a signal representing the magnitude and output the derivative of this signal, optionally an absolute value module 69 for receiving the derivative of the axial offset AO and outputting the absolute value of this derivative, one or more amplifiers 70, each multiplier configured to multiply a signal by a zero, positive or negative coefficient, and two adders 72 for calculating the primary output signal S1 and the secondary output signal S2 from the signals taken into account to calculate the primary output signal S1 and the secondary output signal S2, respectively.

[0101] In one embodiment of the control method, as shown in FIG. 4, comparing the primary output signal S1 with the secondary output signal S2 includes calculating a difference between the primary output signal S1 and the secondary output signal S2, comparing the difference with a lower threshold SINF and / or an upper threshold SSUP, and switching from the command following mode to the output limiting mode.

[0102] The control method includes, for example, switching from the command following mode to the power limiting mode when the difference between the primary output signal S1 and the secondary output signal S2 is less than a lower threshold SINF and / or greater than an upper threshold SSUP.

[0103] For example, switching to the power limiting mode may be timed to remain for at least a predetermined power limiting period from the moment the power limiting mode is enabled.

[0104] The duration of the output limitation is predetermined, for example, 10 seconds (s) or more, particularly 20 seconds or more.

[0105] By maintaining the output limiting mode for a certain minimum period, the primary output P1 and the secondary output P2 can be effectively reduced and restored to equilibrium without quickly switching to the command following mode, even if the primary output P1 and the secondary output P2 quickly return to equilibrium.

[0106] To switch from the command-following mode to the power limiting mode, the control method includes, for example, generating an imbalance logic signal SD indicating that an imbalance exists between the primary output signal S1 and the secondary output signal S2, and generating a timed rebalance request logic signal BP determined in response to the imbalance logic signal to control switching to the power limiting mode.

[0107] The imbalance logic signal SD takes two values ​​(e.g., 0 or 1), one indicating the presence of a significant imbalance that requires a switch to output limit mode, and the other indicating the absence of a significant imbalance that requires a switch to command-follow mode.

[0108] The rebalance request logic signal BP takes two values ​​(e.g., 0 or 1), one corresponding to the command follow mode and the other corresponding to the power limit mode. The rebalance request logic signal BP is timed so that when it changes to a value corresponding to the power limit mode, this value is maintained for a predetermined power limit period.

[0109] As shown in FIG. 4, the control module comprises, for example, a subtractor 74 arranged to determine the difference between the primary output signal S1 and the secondary output signal S2, a comparator 76 for comparing said difference with a lower threshold SINF and / or an upper threshold SSUP and for generating an imbalance logic signal SD in response to the result of the comparison, and a limit request generator 78 for generating a rebalance request logic signal BP in response to the imbalance logic signal SD.

[0110] The target balanced output power PEC is calculated according to the maximum balanced output power PEMAX, and the target balanced output power PEC is advantageously equal to or less than the maximum balanced output power PEMAX.

[0111] As shown in FIG. 5, the control method calculates the maximum balanced output PEMAX as a function of the primary output P1.

[0112] The maximum balanced power PEMAX is advantageously calculated as a function of the primary power P1 minus a non-zero deviation E. This makes it possible to determine a power value less than the primary power P1, for example, in order to calculate power instructions (primary power instruction CP1 and secondary power instruction CP2, described below) that can reduce the power of the reactor 10.

[0113] The value of the deviation E is, for example, 20% to 55%, particularly 20% to 35%, of the nominal operating power of the reactor 10.

[0114] The rated operating power of the reactor 10 is the maximum allowable power during normal operation. This is the desired power output of the reactor 10.

[0115] In one embodiment, the deviation E is constant. In a particular embodiment, the deviation E is selected to be equal to 25% of the nominal power PN of the reactor 10.

[0116] In practice, it has been found that after an imbalance between the primary output P1 and the secondary output P2 is detected, it is possible to restore the balance and reduce the output by bringing the deviation E within the above-mentioned value range.

[0117] Preferably, the difference between the primary output P1 and the deviation E is filtered using a maximum balanced output filter FPEMAX so that the absolute value of its derivative remains below a specified derivative threshold. The maximum balanced output filter FPEMAX is, for example, a low-pass filter, in particular a second-order low-pass filter, although other types of filters may also be used.

[0118] This allows the maximum equilibrium power output PEMAX to be determined from a signal (the difference between the primary power output and the filtered deviation E) whose derivative is limited and corresponds to the load following capability (i.e., responsiveness to changes in power output command) of the reactor 10.

[0119] Preferably, the maximum balanced output filter FPEMAX is configured so that the absolute value of the derivative of the difference between the primary output P1 and the deviation E remains smaller than the maximum absolute value of the load following derivative, for example 5% of the rated output power PN per minute.

[0120] Optionally, after filtering if the latter is performed, the signal resulting from the difference between the primary output P1 and the deviation E is preferably clipped between a minimum value VMIN and / or a maximum value VMAX.

[0121] This ensures that the maximum balanced output power PEMAX remains greater than the minimum value VMIN and / or less than the maximum value VMAX regardless of the current primary output power P1 at which the maximum balanced output power PEMAX is determined, allowing for example for situations where the maximum balanced output power PEMAX is momentarily greater than the rated primary output power PN.

[0122] The minimum value VMIN is for example equal to zero, and the maximum value VMAX is for example equal to 75% of the rated power PN of the reactor 10 .

[0123] As shown in FIG. 5, the control module 56 of the electronic control unit 50 includes, for example, a maximum power calculation module 80 configured to calculate a maximum target balanced power PEMAX.

[0124] As shown in FIG. 5, this maximum output calculation module 80 includes, for example, a subtractor 82 that receives the primary output P1 as an input and subtracts the deviation E therefrom, and optionally, in series with the subtractor 82, a filtering module 84 that applies a maximum balanced output filter FPEMAX to the primary output P1 reduced by the deviation E, and / or a clipping module 86 that receives as an input the value of the primary output P1 minus the deviation E, possibly filtered by the filtering module 84.

[0125] The target balanced output PEC is determined according to the primary output P1, the secondary output P2, and the maximum target balanced output PEMAX, and is set to be equal to or smaller than each of them.

[0126] As shown in FIG. 6, in one embodiment of the control method, the target balanced output PEC is determined as the smallest value among the primary output P1, the secondary output P2, and the maximum balanced output PEMAX.

[0127] The control method includes, for example, a step of calculating a primary power command CP1 and a secondary power command CP2 in a power limit mode so that the primary power P1 matches the primary power command CP1 (i.e., so as to reduce the difference between the primary power P1 and the primary power command CP1) and so that the secondary power P2 matches the primary power command CP2 (i.e., so as to reduce the difference between the secondary power P2 and the secondary power command CP2), and controlling the nuclear power plant 2. The primary power command CP1 and the secondary power command CP2 used to control the nuclear power plant 2 in the power limit mode are calculated according to the target equilibrium power PEC.

[0128] In a particular embodiment, the primary output command CP1 and the secondary output command CP2 are calculated as equal to the target balanced output PEC and are optionally filtered by applying a target balanced output filter FPEC, which is preferably a low-pass filter.

[0129] The control module 56 of the electronic control unit 50 includes, for example, an instruction calculation module 90 configured to calculate a primary output instruction CP1 and a secondary output instruction CP2.

[0130] An instruction calculation module 90 receives as inputs the primary output P1, the secondary output P2, and the maximum balanced output PEMAX, and provides as outputs the primary output instruction CP1 and the secondary output instruction CP2.

[0131] The indication calculation module includes, for example, a selector 92 configured to select the lowest value signal from the primary output P1, the secondary output P2, and the maximum balanced output PEMAX.

[0132] Optionally, the control unit 50 comprises a balanced output filtering module 94 for filtering the target balanced output PEC by applying a target balanced output filter FPEC.

[0133] Optionally, in command-following mode, the control method includes calculating a primary output command CP1 and a secondary output command CP2 as equal to the primary output P1 and secondary output P2, respectively.

[0134] In the command following mode, the primary power command CP1 and secondary power command CP2 calculated in this manner are not used in the actual control of the nuclear power plant 2 in principle, and the actual control is carried out according to the power operation command COP.

[0135] However, this provides a safety net in case control system 40 switches to the power limiting mode without actually detecting an output imbalance. In such a case, because rebalancing request logic signal BP does not request a switch to the power limiting mode, primary output command CP1 is considered equal to primary output P1 and secondary output command CP2 is considered equal to secondary output P2, and therefore control system 40 does not change primary output P1 and secondary output P2 despite the untimely switch to the power limiting mode.

[0136] The instruction calculation module 90 includes, for example, a switching module 96 that receives as inputs the primary output P1, the secondary output P2, and a possibly filtered target balanced output PEC, and provides as outputs a primary output instruction CP1 and a secondary output instruction CP2, the switching module 96 being controlled by a rebalancing request logic signal BP so that the primary output instruction CP1 is equal to the primary output in instruction following mode or the target balanced output PEC (possibly filtered) in output limit mode, and the secondary output instruction CP2 is equal to the secondary output in instruction following mode or the target balanced output PEC (possibly filtered) in output limit mode.

[0137] In one embodiment, each module and / or filter of electronic control unit 50 is implemented in the form of a software application including software code instructions stored in a computer memory or medium and executable by a processor.

[0138] Alternatively, at least one module and / or at least one filter of the electronic control unit 50 is in the form of an Application Specific Integrated Circuit (ASIC) or a programmable logic circuit, for example a Field Programmable Gate Array (FPGA).

[0139] In operation, by default, the control system 40 controls the nuclear power plant 2 in command-following mode, in which the control system 40 controls the nuclear power plant 2 so that the primary output P1 and secondary output P2 follow the power operation command.

[0140] If an imbalance is detected by comparing the primary output signal S1 and the secondary output signal S2, the control system 40 enters a power limiting mode in which the primary output P1 and the secondary output P2 are controlled according to a target balanced output PEC calculated by the control system 40 that is less than or equal to the primary output P1 and less than or equal to the secondary output P2.

[0141] In the power limiting mode, the control system 40 calculates a primary power command CP1 and a secondary power command CP2, for example, from the target balanced power PEC, and controls the nuclear power plant so that the primary power P1 matches the primary power command CP1 and the secondary power P2 matches the secondary power command CP2.

[0142] The primary output command CP1 is, for example, equal to the target balanced output PEC, possibly filtered, in particular filtered by a low-pass filter, and the secondary output command CP2 is, for example, equal to the target balanced output PEC, possibly filtered, in particular filtered by a low-pass filter.

[0143] The output limit mode is maintained for the set output limit period, and then the mode returns to the instruction follow-up mode.

[0144] Optionally, in command-following mode, control system 40 calculates the primary output command CP1 as equal to the primary output P1 and the secondary output command CP2 as equal to the secondary output P2.

[0145] The present invention makes it possible to maintain the nuclear power plant 2 in its normal operating range in the event of a power imbalance by switching to a power limiting mode implemented by a control system already controlling the nuclear power plant 2 in command following mode, and by avoiding the intervention of protection systems capable of shutting down the nuclear power plant, for example by lowering the shutdown cluster.

[0146] The power limit mode can be implemented at all power levels of the nuclear power plant, i.e., regardless of the current power operation instructions when the imbalance is detected.

[0147] This can be implemented using the control system 40. This can be enabled during high amplitude normal operation transients or accidental transients from the nuclear power plant 2, which can cause significant power imbalance.

[0148] This can be done without intervention by the protection system and is not specifically limited to the use of protection system equipment. Without intervention by the protection system of Nuclear Power Plant 2, there is likely to be only a minor impact on the Safety Report of Nuclear Power Plant 2. Implementation of this control method does not require the re-creation of the Safety Report of Nuclear Power Plant 2, except for the amendment of the Safety Report chapters specific to a particular project where transients modified by technological innovations or limiting systems are taken into account.

[0149] The present invention is not limited to the above-described embodiment and modifications, and other embodiments and modifications are possible.

[0150] For example, in the embodiment shown in FIG. 6, in the power limiting mode, the primary power command P1 and the secondary power command P2 are both calculated as the target balanced power PEC filtered by the same target balanced power filter PEC.

[0151] Alternatively, it is possible to provide different primary and secondary filters, with the primary power command CP1 being equal to the target balanced output power PEC filtered by the primary filter and the secondary output power command CP2 being equal to the target balanced output power PEC filtered by the secondary filter.

[0152] It is also possible to provide identical primary and secondary filters, with the primary power command CP1 being equal to the target balanced power PEC filtered by the primary filter, and the secondary power command CP2 being equal to the target balanced power PEC filtered by the secondary filter.

[0153] Furthermore, the calculation of the primary output P1 and the secondary output P2 is not limited to the calculation example shown above, and other calculation methods are also possible.

[0154] In one embodiment, as shown in FIG. 7, in which like elements as in FIGS. 1-6 are numbered the same, the first sensor whose measurements are used to calculate the primary output P1 may be, for example: a cold branch temperature sensor 100 in each cold branch of the primary circuit 4 for measuring the temperature of the water circulating in that cold branch, and a cold branch flow rate sensor 102 for measuring the flow rate of the water circulating in that cold branch; a hot branch temperature sensor 104 for measuring the temperature of water circulating through each hot branch of the primary circuit 4, and a hot branch flow rate sensor 106 for measuring the flow rate of water circulating through each hot branch; and a pressurizer pressure sensor 108 for measuring the pressure within the pressurizer 24.

[0155] The calculation of the primary power P1 performed by the primary power calculation module of the electronic control unit 50 is, for example, calculating a mean cold branch temperature TBFM as an average value of the cold branch temperatures measured by the cold branch temperature sensor 100, optionally filtered, preferably by a low pass filter; calculating a mean cold branch flow DBFM as an average value of the cold branch flow measured by the cold branch flow sensor 102, optionally filtered, preferably by a low pass filter; calculating a mean hot branch temperature TBCM as an average value of the hot branch temperatures measured by the hot branch temperature sensors 104, optionally filtered, preferably by a low pass filter; calculating a mean hot branch flow rate DBCM as an average value of the hot branch flow rates measured by the hot branch flow sensor 106, optionally filtered by a filter, preferably a low pass filter; and calculating a primary output P1 according to the average cold branch temperature TBFM, the average cold branch flow rate DBFM, the average hot branch temperature TBCM, and the average hot branch flow rate DBCM.

[0156] The calculation of the primary power P1 performed by the primary power calculation module of the electronic control unit 50 is, for example, Calculating the average cold branch enthalpy HBFM according to the average cold branch temperature measured by the pressurizer pressure sensor 108 and the pressurizer pressure PPR; Calculating the average hot branch enthalpy HBCM according to the average hot branch temperature TBCM and the pressurizer pressure PPR; and calculating a primary power output P1, which is equal to the average primary thermal power supplied from the reactor to the primary circuit 4, as the product of a calibration coefficient K and a function FPTH for calculating the primary thermal power output, using the average cold branch flow rate DBFM, the average hot branch flow rate DBCM, the average cold branch enthalpy HBFM, the average hot branch enthalpy HBCM, the average cold branch temperature TBFM, the average hot branch temperature TBCM, and the pressurization pressure PPR as input data.

[0157] The function for calculating the primary heat power FPTH is preferably based on the heat balance of the primary circuit 4 .

[0158] The calibration factor K is determined during routine testing using the secondary enthalpy balance required to determine the heat output. The calibration factor K is used to adjust the primary heat output.

[0159] In this way, the primary output P1 can be determined based on measurements provided by temperature, flow and pressure sensors, instead of using, for example, a neutron sensor 42.

[0160] In one embodiment, as shown in FIG. 7, the second sensor, whose measurements are used to calculate the secondary output P2, includes, for example, for each steam generator 8, a steam flow sensor 110 for measuring the flow rate of steam in the secondary circuit 6 at the outlet of the steam generator 8, a steam pressure sensor 112 for measuring the pressure in the secondary circuit 6 at the outlet of the steam generator 8, a steam temperature sensor 114 for measuring the temperature in the secondary circuit 6 at the outlet of the steam generator 8, a water pressure sensor 116 for measuring the pressure of water entering the steam generator 8 in a liquid state in the secondary circuit 6, and a water temperature sensor 118 for measuring the temperature of water at the inlet to the steam generator 8 in the secondary circuit 6.

[0161] The calculation of the primary power P2 performed by the secondary power calculation module of the electronic control unit 50 is, for example, Calculating an input enthalpy HE for each steam generator 8 according to the water temperature TEAU and water pressure PEAU at the inlet of the steam generator 8 measured by the water temperature sensor 118 and the water pressure sensor 116, and calculating an output enthalpy HV according to the steam temperature and steam pressure at the outlet of the steam generator measured by the steam temperature sensor 114 and the steam pressure sensor 112; and calculating, for each steam generator 8, a secondary output P2 as the sum of the product of the steam flow rate DV at the outlet of that steam generator measured by the steam flow rate sensor 110 and the difference between the output enthalpy HV of that steam generator and the input enthalpy HE of that steam generator. The primary power P2 is calculated according to the following formula:

number

[0162] As shown in Figure 8, in which similar elements to those in Figures 1 to 7 are given the same reference numerals, a secondary circuit 6 having multiple steam generators 8 supplying the same turbine 28 includes, for example, a steam drum 120 ("steam collector") that receives steam generated by the steam generators 8 and distributes the generated steam to the turbines 28, and a water drum 122 (or "water distributor") that receives water from the condenser 32 and distributes this water to the different steam generators 8.

[0163] Furthermore, the secondary circuit 6 includes, for example, a circuit for discharging steam from the secondary, bypassing the turbine 28, which will be referred to below as GCTC, an acronym for "groupe de contournement vapor au condenseur" (group of steam bypasses at the condenser), and is given the reference number 124. The GCTC 124 is configured to direct steam from the outlet of the steam drum 120, bypassing the turbine 28, to the inlet of the condenser 32.

[0164] The GCTC 124 includes one or more control actuators 126, such as valves controlled by the nuclear power plant control system 40, for controlling the flow of steam through the GCTC 124, which are controlled, for example, via a logical lock signal GCTC_dev that takes two values ​​(e.g., 0 and 1) (one does not allow opening and requests that the GCTC 124 be locked, and the other allows opening and requests that the GCTC be unlocked), and an opening control signal GCTC_com that requests the opening of the valve of the GCTC 124, for example, as a percentage of opening between a minimum opening and a maximum opening.

[0165] A nuclear power plant, for example, includes one or more steam consumers 127. Each steam consumer 127 is connected to the secondary circuit 6 and takes in steam from the secondary circuit 6, preferably at the outlet of the steam drum 120.

[0166] The steam consuming device 127 is, for example, a dryer / superheater.

[0167] Steam consumers 127 do not include turbine 28 and GCTC 124 .

[0168] In one embodiment, as shown in FIG. 8, the second sensor may be, for example, a turbine pressure sensor 128 configured to measure the pressure within the turbine 28, preferably at the inlet of a first wheel of the turbine 28 when the turbine 28 includes multiple wheels each defining a turbine stage; a steam drum pressure sensor 130 for measuring the pressure of steam in the steam drum; a steam drum temperature sensor 134 for measuring the temperature of the steam in the steam drum; a water drum temperature sensor 138 for measuring the temperature of the water in the water drum; a water drum pressure sensor 140 for measuring the pressure of the water in the water drum; and one or more steam withdrawal rate sensors 142 that each measure the rate at which steam is withdrawn from the secondary circuit 6 by the steam consumer 127 .

[0169] For example, the primary output P2 is calculated according to the following formula: If GCTC is unlocked:

number

number

[0170] K GCTC is the adjustment factor for the heat output exhausted to the GCTC124, expressed as W / (Pa × GCTC124 opening (%)),

[0171] D jis the mass flow rate of steam consumed by the steam consumer with index j (kg / s),

[0172] K j is the adjustment factor for the heat power discharged to the steam consumer with index j.

[0173] Such calculation of the secondary power P2 is performed in particular by sensors arranged in the steam drum 120 and the water drum 122, without the need to equip each steam generator with one or more sensors at the inlet of the steam generator 8 and at the outlet of the steam generator 8. This allows the number of sensors to be reduced. [Explanation of symbols]

[0174] 2. Nuclear Power Plants 4 Primary circuit 6 Secondary circuit 8 Steam Generator 10 nuclear reactor 20 Control Cluster 40 Control System P1 Primary Output P2 Secondary output S1 Primary output signal S2 Secondary output signal

Claims

1. A control method implemented by an automatic control system (40) for controlling a pressurized water nuclear power plant (2) including a primary circuit (4) for circulating water incorporating a nuclear reactor (10), a secondary circuit (6) for circulating water, and N steam generators (8), where N is an integer greater than or equal to 1, each steam generator (8) configured to transfer thermal energy from the primary circuit (4) to the secondary circuit (6) accompanied by the generation of steam in the secondary circuit (6); calculating a primary power (P1), representing the thermal power generated by the nuclear reactor (10), in response to measurements of a first operating parameter of the pressurized water nuclear power plant (2) measured by a first sensor associated with operation of the primary circuit (4); and calculating a secondary power (P2), representing the thermal power transferred by the steam generator (8) from the primary circuit (4) to the secondary circuit (6), in response to a second operating parameter of the pressurized water nuclear power plant (2) measured by a second sensor associated with operation of the secondary circuit (6); detecting a possible imbalance between the primary output (P1) and / or a primary output signal (S1) calculated depending on at least one variable indicative of a variation of the primary output (P1) and the secondary output (P2) and / or a secondary output signal (S2) calculated depending on at least one variable indicative of a variation of the secondary output (P2); If no imbalance is detected, implementing a command-following mode in which the pressurized water nuclear power plant (2) is controlled in accordance with a power operation command (COP) received by an automatic control system (40) so that the primary output (P1) and the secondary output (P2) follow the power operation command (COP); and automatically implementing a power limiting mode, when an imbalance is detected, by the automatic control system (40) calculating a target balanced power output (PEC) that is less than or equal to the primary power output (P1) and less than or equal to the secondary power output (P2), and controlling the pressurized water nuclear power plant (2) in accordance with the target balanced power output (PEC).

2. 2. A method according to claim 1, characterized in that the secondary power (P2) is determined by calculating the thermal power transferred by each steam generator (8) from the primary circuit (4) to the secondary circuit (6) and calculating the sum of these thermal powers.

3. 3. The control method according to claim 1 or claim 2, wherein the primary output signal (S1) is calculated in response to the primary output (P1), a filtered derivative of the primary output (P1), an axial offset (AO) of the reactor (10), a filtered derivative of the axial offset (AO) of the reactor (10), a motion signal (PG) of a control cluster (20) and / or a filtered derivative of the motion signal (PG) of the control cluster (20).

4. 4. The control method of claim 3, wherein the primary output signal (S1) is calculated as a sum of the primary output (P1) and one or more of a filtered derivative of the primary output (P1) multiplied by a primary output coefficient (KP1), an absolute value of a filtered derivative of an axial offset (AO) multiplied by an axial offset coefficient (KAO), and a filtered derivative of a control cluster motion signal (PG) multiplied by a motion signal coefficient (KPG).

5. 5. The control method according to claim 1, wherein the secondary output signal (S2) is calculated in response to the secondary output (P2), a steam pressure (PV) representing the steam pressure at the outlet of the steam generator (8), a filtered derivative of the steam pressure (PV), a feedwater temperature (TE) representing the water temperature at the inlet of the steam generator (8), a filtered derivative of the feedwater temperature (TE), a feedwater flow rate (DE) representing the water flow rate at the inlet of the steam generator (8), and / or a filtered derivative of the feedwater flow rate (DE).

6. 6. The control method of claim 5, wherein the secondary output signal (S2) is calculated as a sum of the secondary output (P2) and one or more of a filtered derivative of the steam pressure (PV) multiplied by a steam pressure coefficient (KPV), a filtered derivative of the feedwater temperature (TE) multiplied by a feedwater temperature coefficient (KTE), and a filtered derivative of the feedwater flow rate (DE) multiplied by a feedwater flow rate coefficient (KDE).

7. 7. The control method according to claim 1, wherein the step of detecting a possible imbalance comprises comparing the difference between the primary output signal (S1) and the secondary output signal (S2) with a lower threshold and / or an upper threshold.

8. 8. The control method of claim 7, wherein the step of detecting the imbalance includes generating a logic signal requesting rebalancing (BP) and commanding a switch to the power limiting mode when the difference is less than the lower threshold and / or greater than the upper threshold.

9. The control method of any one of claims 1 to 8, wherein the power limiting mode is enabled for a power limiting period determined from the step of detecting the imbalance.

10. 10. The control method according to claim 1, wherein the target balanced output (PEC) is calculated according to a maximum balanced output (PEMAX), and the target balanced output (PEC) is equal to or smaller than the maximum balanced output.

11. 11. The control method of claim 10, wherein the maximum balanced power (PEMAX) is calculated as a function of the primary power (P1) minus a non-zero deviation (E).

12. 12. The control method of claim 11, wherein the primary output (P1) minus the non-zero deviation (E) is filtered so that the absolute value of its derivative remains below a predetermined derivative threshold.

13. 13. A control method according to claim 11 or 12, comprising clipping the maximum balanced power (PEMAX) to be less than a specified maximum value (VAMX) and / or greater than a specified minimum value (VMIN).

14. 14. The control method of claim 10, wherein the target balanced power output (PEC) is determined as the minimum of the primary power output (P1), the secondary power output (P2) and the maximum balanced power output (PEMAX).

15. 15. The control method according to claim 1, further comprising: in the power limiting mode, calculating a primary power command (CP1) and a secondary power command (CP2) according to the target equilibrium power (PEC), and controlling the pressurized water nuclear power plant (2) so that the primary power (P1) matches the primary power command (CP1) and the secondary power (P2) matches the secondary power command (CP2).

16. 16. The control method of claim 15, wherein in the power limiting mode, the primary power command (CP1) is calculated to be equal to the target balanced power (PEC), and the secondary power command (CP2) is calculated to be equal to the target balanced power (PEC).

17. A control method as described in claim 15, characterized in that in the output limiting mode, the primary output command (CP1) is calculated as equal to the target balanced output (PEC) filtered or filtered by a low-pass filter, and / or the secondary output command (CP2) is calculated as equal to the target balanced output (PEC) filtered or filtered by a low-pass filter.

18. An automatic control system (40) for a pressurized water nuclear power plant (2), configured to carry out the control method according to any one of claims 1 to 17.

19. 19. A pressurized water nuclear power plant (2) comprising a primary circuit (4) for the circulation of water incorporating a nuclear reactor (10), a secondary circuit (6) for the circulation of water, and N steam generators (8), where N is an integer greater than or equal to 1, and including the automatic control system (40) of claim 18, wherein each steam generator (8) is configured to transfer thermal energy from the primary circuit (4) to the secondary circuit (6) accompanied by the generation of steam in the secondary circuit (6).

20. A computer program product recordable on a computer medium or in a computer memory and executable by a processor, the computer program product comprising software code instructions for carrying out the control method according to any one of claims 1 to 17.

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