Motor-Lead Screw Control Rod Drive With Integral Nut Engagement
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Solution Overview
Problem
Existing control rod driving mechanisms for nuclear reactors face challenges in achieving continuous movement, precise positioning, compact structure, high reliability, and long service life, particularly due to issues with separable nuts causing rapid wear and engagement deviations, as well as structural complexities and space constraints.
Innovation Solution
A motor-leadscrew type control rod driving mechanism using integral nuts and a helical transmission pair to ensure continuous movement and accurate positioning, with a core rod connected to the control rod assembly, and an elastic mechanism for emergency rod dropping, ensuring stable engagement and reducing wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If separable and closeable nuts are used in the leadscrew-roller-nut driving mechanism, then the mechanism can be disassembled for maintenance, but the engagement deviation between the nut and lead screw causes rapid wear and reduces service life
Solution Approach 1:
The patent integrates the nut and lead screw into a unified structure where the nut is fixed to the driving shaft, eliminating the separable connection. This merging ensures consistent engagement between the roller and lead screw thread, preventing wear caused by repeated engagement and disengagement, while maintenance is performed by replacing the entire integrated assembly.
2Length of stationary object
If the control rod driving mechanism is designed as built-in type, then the overall height of the reactor is reduced, but the components must withstand high temperature, radiation, and corrosion which challenges material selection and reliability
Solution Approach 1:
The patent extracts the motor and control system from the reactor core area, placing them in the upper guide tube assembly that is accessible from the top. This allows the critical electronic and motor components to operate in more favorable conditions while still achieving compact reactor height through optimized spatial arrangement of the remaining components.
3Speed
If the leadscrew and roller-nut are completely disengaged during emergency shutdown, then the control rod can be quickly released, but the re-engagement causes relative position deviation and increases the difficulty of re-engagement
Solution Approach 1:
The patent incorporates a spring-loaded retention mechanism that maintains preliminary engagement between the roller and lead screw thread even during emergency shutdown. The spring force ensures that when normal operation resumes, the components are already in the correct engagement position, eliminating the need for complex re-alignment procedures.
4Measurement precision
If the claw assembly moves frequently for millions of times, then the control rod can be precisely positioned, but serious mechanical wear occurs affecting service life
Solution Approach 1:
The patent replaces the mechanical claw assembly with a magnetic coupling system that uses magnetic fields to transmit motion and force. This substitution eliminates direct mechanical contact and wear between moving parts, allowing for precise positioning through magnetic field control while dramatically extending the service life of the positioning mechanism.
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
The mechanism achieves high reliability and extended service life by maintaining stable engagement of the helical transmission pair, preventing rapid wear and impact during emergency operations, and reducing structural impacts on the reactor core.
Implementation Method 1
a helical transmission pair which includes a leadscrew having an inner hollow structure and a first nut and a second nut both engaged with the leadscrew; a core rod which is connected to a control rod assembly of a nuclear reactor to drive the control rod assembly to move
Implementation Method 2
a rod dropping device which includes an elastic mechanism, wherein the first nut and the second nut are respectively fixedly connected to two ends of the motor shaft, and the leadscrew passes through the first nut, the motor shaft and the second nut in sequence from bottom to top to be fixedly connected to the rod dropping device
Data Source
Figure 1
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AI summary
Provided are a motor-leadscrew type control rod driving mechanism and a method for driving the same. Nuts are driven by using a controllable motor, rotation of the nuts is converted into linear motion of a leadscrew (22) by means of a helical transmission pair (200), the leadscrew (22) is connected to a control rod assembly (1) by means of a core rod (20), so that continuous movement and accurate positioning of the control rod assembly (1) can be achieved, and the reliability is high; in addition, integral nuts are used to drive the leadscrew (22) to always maintain correct engagement of the helical transmission pair (200), thereby avoiding the problem of too rapid wear caused by engagement deviation of separable and closeable nuts, and prolonging the service life of the driving mechanism. The helical transmission pair (200) has good impact and swing resistance, and would not be disengaged due to emergency rod dropping or refueling, so that an impact problem caused by re-engagement and connection is avoided, engagement precision and transmission stability are ensured, the wear resistance and reliability of the transmission component are improved, and the service life of the transmission component is prolonged.