Method and assembly for controlling a nuclear reactor, nuclear reactor equipped with such an assembly

17:

• A method for controlling a nuclear reactor, the nuclear reactor having a core comprising a plurality of nuclear fuel assemblies, a primary circuit for cooling the core in which a primary heat transfer fluid containing a neutron poison circulates, a unit allowing neutron poison to be injected into the primary heat transfer fluid, and a unit provided for injecting water into the primary circuit, the method comprising the following steps:
• S10/ acquiring a reactor power program to be supplied by the nuclear reactor, this program comprising at least one reactor power variation from a first power to a second power;
• S20/ acquiring current values of a plurality of operating parameters of the nuclear reactor, comprising at least one parameter characterizing a core power supplied by the core of the reactor and one parameter characterizing a neutron flux distribution in the core;
• S30/ iteratively, implementing the following sub-steps:
• S31/ generating an injection sequence of neutron poison and/or water into the primary heat transfer fluid covering a given time interval,
• S32/ calculating an evolution of at least one magnitude characteristic of a state of the core of the nuclear reactor during said given time interval using the acquired reactor power program, the acquired current values of the operating parameters and the generated injection sequence, the evolution being calculated with the aid of a predictive model of the core of the reactor;
• S33/ evaluating a cost function, using the calculated evolution;
• sub-steps S31/ to S33/ being repeated until a cost function convergence criterion is met;
• S40/ communicating to an operator an optimum injection sequence allowing the cost function convergence criterion to be met, the operator controlling the neutron poison and water injection units as a function of the optimum injection sequence;
• steps S20/ and S30 being repeated with a time period less than 60 minutes.

21:

• The control method according to claim 17, wherein the cost function convergence criterion comprises meeting at least one constraint selected from the following list:
• a deviation between said parameter characterizing the neutron flux distribution in the core and a reference value during said given time interval remains constantly below a determined limit;
• a quantity of neutron poison injected per unit of time during said given time interval remains below a determined limit;
• a quantity of water injected per unit of time during said given time interval remains below a determined limit.

23:

• The control method according to claim 17, wherein step S30/ comprises a sub-step S35/ for determining an optimum slope for an evolution of the power as a function of time during the power evolution from the first power to the second power, sub-step S35/ comprising the following operations:
• S351/ calculating an evolution of the at least one magnitude characteristic of the state of the core of the nuclear reactor during said power variation with the aid of the predictive model of the core of the reactor, for several values of slope, the injection of neutron poison or water per unit of time being considered constantly equal to the maximum possible;
• S352/ evaluating the cost function, using the variation calculated for each slope value;
• S353/ selecting the slope value minimizing the cost function.

26:

• The control method as claimed in claim 25, wherein the equations characterizing reactivity at each level take into account one or more of the following effects:
• effect due to a variation in the temperature of the primary heat transfer fluid at said level;
• effect due to a variation in the power supplied by the core at said level;
• effect due to displacement of groups of control rods;
• effect due to a variation in a concentration of neutron poison in the primary heat transfer fluid;
• and
• effect due to a variation in a concentration of xenon in the nuclear fuel assemblies at said level.

30:

• A control assembly for a nuclear reactor, the nuclear reactor having a core comprising a plurality of nuclear fuel assemblies, a primary circuit for cooling the core, in which a primary heat transfer fluid containing a neutron poison circulates, a unit allowing the neutron poison to be injected into the primary heat transfer fluid, and a unit provided for injecting water into the primary circuit, the neutron poison and water injection units being controlled by an operator, the control assembly comprising:
• a user interface, configured so that a user enters a power program to be supplied by the nuclear reactor, this program comprising at least one power variation from a first power to a second power;
• a unit for acquiring current values of a plurality of operating parameters of the nuclear reactor, comprising at least one parameter characterizing the power supplied by the core of the reactor and one parameter characterizing a neutron flux distribution in the core;
• and
• a calculation unit including:
• an optimization algorithm, programmed to generate an injection sequence of neutron poison and/or water in the primary heat transfer fluid covering a given time interval;
• a predictive model of the core of the reactor, programmed to calculate an evolution of at least one magnitude characteristic of a state of the core of the nuclear reactor during said given time interval, using the acquired reactor power program, the acquired current values of the operating parameters and the generated injection sequence;
• and
• a cost module configured to calculate a cost function, using the evolution calculated by the predictive model;
• the optimization algorithm being programmed to iteratively generate an optimum injection sequence, to calculate the evolution of the at least one corresponding magnitude characteristic by the predictive model of the core, to evaluate the corresponding cost function by the cost module, until a cost function convergence criterion is met;
• and
• the control assembly also being configured to display the optimum injection sequence, in other words, that for which the cost function convergence criterion has been met, on the user interface, so that the optimum injection sequence is implemented by the operator.

31:

• The control assembly according to claim 30, wherein the calculation unit comprises a slope module programmed to determine an optimum slope for an evolution of reactor power as a function of time during the power variation from the first power to the second power, said slope module being programmed to:
• cause the predictive model of the core calculate the evolution of at least one magnitude characteristic of the state of the core of the nuclear reactor during said power variation, for several slope values, the neutron poison or water injection per unit time being considered constantly equal to the maximum possible;
• cause the cost module evaluate the cost functions corresponding to each slope value, using the evolution calculated for each slope value;
• and
• select the slope value that minimizes the cost function.

32:

• A nuclear reactor including a core comprising:
• a plurality of nuclear fuel assemblies;
• a primary circuit for cooling the core in which a primary heat transfer fluid containing a neutron poison circulates;
• a unit allowing neutron poison to be injected into the primary heat transfer fluid;
• a unit provided for injecting water into the primary circuit;
• and
• the control assembly according to claim 30, the neutron poison and water injection units being controlled by an operator.