Nuclear-reactor control-absorber drive mechanism and corresponding monitoring method and nuclear reactor

A drive mechanism for at least one nuclear reactor control absorber, the drive mechanism comprising:

• at least one electric motor of a stepping typing comprising:
• a stator having at least a first phase, a second phase, and a third phase, and
• a rotor;
• an electric power supply, electrically connected to each of the first phase, the second phase and the third phase of the stator;
• a controller of the electric power supply, programmed so that the electric power supply delivers an electric pulse to each of the first phase, the second phase and the third phase at a current frequency, the electric pulse forming a control step with a shape adapted to control the at least one electric motor, the rotor being moved per unit of time by a number of rotation steps depending on the current frequency;
• a kinematic chain arranged to couple the rotor to the at least one nuclear reactor control absorber, the kinematic chain being arranged to convert a rotational movement of the rotor into a translational movement of the at least one nuclear reactor control absorber in a core of a nuclear reactor, with no possibility of slipping;
• and
• a monitor configured for monitoring a potential situation of increase to overspeed of the at least one nuclear reactor control absorber, the monitor comprising:
• at least two mutually independent monitoring units, each of the at least two mutually independent monitoring units being connected to terminals of one of the first phase, the second phase and the third phase, each of the at least two mutually independent monitoring units being configured to:
• measure a number of control steps delivered to the first phase, the second phase or the third phase during a time window of a preset duration or measure the number of rotation steps of the rotor during a time window of preset duration;
• and
• compare the number of control steps measured with a preset maximum or compare the number of rotation steps measured with a preset maximum.

A method for monitoring a potential situation of increase to overspeed of a nuclear reactor control absorber equipped with a drive mechanism comprising:

• at least one electric motor of a stepping typing comprising:
• a stator having at least a first phase, a second phase, and a third phase, and
• a rotor;
• an electric power supply, electrically connected to each of the first phase, the second phase and the third phase of the stator;
• a controller of the electric power supply, programmed so that the electric power supply delivers an electric pulse to each of the first phase, the second phase and the third phase at a current frequency, the electric pulse forming a control step with a shape adapted to control the at least one electric motor, the rotor being moved per unit of time by a number of rotation steps depending on the current frequency;
• a kinematic chain arranged to couple the rotor to the at least one nuclear reactor control absorber, the kinematic chain being arranged to convert a rotational movement of the rotor into a translational movement of the at least one nuclear reactor control absorber in a core of a nuclear reactor, with no possibility of slipping;
• the method including at least two mutually independent monitoring steps, each of the at least two mutually independent monitoring steps comprising:
• measuring, across the terminals of one of the first, second and third phases, a number of control steps delivered to said phase during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration;
• and
• comparing the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.