Stepping Motor Control Absorber Drive Overspeed Monitoring
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Solution Overview
Problem
Current drive mechanisms for nuclear reactor control absorbers are prone to rapid reactivity injections due to motor control failures, leading to uncontrollable neutronic power increases, which are difficult to detect and respond to in time, especially in SMR reactors without cover crossmembers, resulting in safety concerns.
Innovation Solution
A drive mechanism with independent monitoring units that measure and compare the number of control steps or rotation steps within a preset time window to detect overspeed conditions, allowing for immediate cutoff of the electric power supply to prevent excessive reactivity injection, featuring a kinematic chain that converts rotational movement into translational movement without slipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DC or AC rotary motors are used to drive control absorbers, then the drive mechanism can achieve nominal speed control, but the rise speed cannot be reliably limited during failures due to torque variations and efficiency changes
Solution Approach 1:
The patent replaces traditional DC or AC rotary motors with a stepping motor that is driven by electronic pulses. This substitution allows precise control of the rotor's rotational speed through pulse frequency, eliminating the reliability issues associated with torque variations and efficiency changes in traditional motors. The electronic control system directly correlates pulse frequency with absorber rise speed, ensuring reliable speed limitation even during failures.
2Measurement precision
If neutron flux measurement is used to detect reactivity injection, then the detection can provide information about core conditions, but the response time is too slow (several seconds to tens of seconds) to prevent prompt criticality
Solution Approach 1:
The patent implements a monitoring device that detects overspeed conditions of the control absorber before they result in significant reactivity injection. By monitoring the rotational speed of the absorber drive mechanism and predicting potential failures, the system can take preliminary action to prevent prompt criticality, rather than waiting for neutron flux measurements that come too late.
Solution Approach 2:
The patent employs a feedback mechanism where the monitoring device continuously monitors the rotational speed of the control absorber and provides real-time information to the control system. This feedback loop enables the system to detect overspeed conditions immediately and respond by limiting reactivity injection, creating a closed-loop control system that prevents accidents before they occur.
3Speed
If pawl mechanisms are used to mechanically limit absorber movement speed, then the rise speed can be constrained, but the mechanism becomes mechanically complex and occupies substantial radial bulk
Solution Approach 1:
The patent replaces mechanical speed-limiting mechanisms like pawls with an electronically controlled stepping motor system. The motor's rotational speed is controlled through electronic pulse frequency, eliminating the need for complex mechanical speed-limiting components. This substitution reduces mechanical complexity and radial bulk while maintaining precise speed control capability.
4Ease of operation
If DC rotary motors with voltage control are used, then nominal speed can be controlled, but significant margins (factor of 3) must be applied in safety studies due to evolving operating conditions
Solution Approach 1:
The patent replaces DC rotary motors with voltage control with electronically controlled stepping motors. The stepping motor system uses electronic pulse frequency to directly control rotor speed, creating a more reliable and predictable relationship between control input and actual speed. This eliminates the need for large safety margins in the factor of 3, as the electronic control system maintains consistent performance across varying operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and safe intervention by measuring command parameters rather than actual movement speed, reducing reactivity injection and maintaining safety margins, thus preventing prompt criticality accidents.
Implementation Method 1
at least one electric motor of the stepping type including a stator having at least first, second and third phases and a rotor
Implementation Method 2
a kinematic chain arranged to couple the rotor to the control absorber, the kinematic chain being arranged to convert a rotational movement of the rotor into a translational movement of said control absorber in the core of the reactor, with no possibility of slipping
Data Source
AI summary
A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.