Nuclear Control Rod Flexure Joint Design
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Solution Overview
Problem
Current control rod assemblies in nuclear reactors face limitations in lateral deflection, manufacturing efficiency, and assembly complexity due to the existing flexure joint design, which restricts lateral movement and requires precise hole drilling for pin insertion, leading to potential disengagement and manufacturing delays.
Innovation Solution
A ball and socket flexible joint coupling is introduced at the finger attachment, allowing increased lateral deflection limited by reactor internal components, enabling preloaded threaded joints with thicker finger walls and eliminating the need for pin drilling by using a weld or crimp to secure the control rod position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pin is welded into a tightly toleranced hole drilled after rod installation to lock the control rod, then the control rod is secured against rotation and disengagement, but the manufacturing process is slowed and there is risk of dropped rods if the hole is drilled too deeply
Solution Approach 1:
The patent applies preliminary action by drilling the hole and inserting the pin before installing the control rod into the spider assembly, rather than after. This allows the hole to be precisely positioned and the pin to be securely installed in advance, eliminating the risk of dropped rods during final assembly and avoiding delays in the manufacturing process.
Solution Approach 2:
The patent segments the assembly process into distinct stages: first preparing the finger with the drilled hole and pin, then installing the control rod. This segmentation allows each component to be prepared independently with proper tolerances and quality control, improving both reliability and manufacturing efficiency.
2Strength
If the spider finger hole diameter is made large enough to clear the shoulder on the control rod upper end plug, then the threaded joint can be preloaded and react lateral bending loads, but the wall thickness of the finger becomes very small which adversely impacts manufacturing
Solution Approach 1:
The patent introduces a reduced diameter section (flexure joint) of the control rod that extends into the spider finger, creating a stepped configuration. This dimensional change allows the shoulder to be positioned at a different location, enabling the finger hole to be smaller while still providing adequate clearance and load-bearing capability for the threaded joint.
Solution Approach 2:
The patent applies local quality by creating a reduced diameter section specifically at the spider finger interface location, while maintaining the full diameter of the control rod elsewhere. This localized modification provides the necessary clearance and load distribution at the critical interface without affecting the overall control rod structure or requiring excessive finger wall thickness.
3Adaptability or versatility
If a reduced diameter section is incorporated at the control rod connection to the spider finger, then lateral deflection is enabled to compensate for misalignment and reduce wear, but lateral deflection must be limited by the spider finger to prevent overload of the joint
Solution Approach 1:
The patent changes the geometric parameter of the control rod by incorporating a reduced diameter section, which creates a flexure joint that enables controlled lateral deflection. The specific dimensions of this reduced section are designed to provide the necessary flexibility for misalignment compensation while maintaining adequate strength to prevent joint overload.
Solution Approach 2:
The reduced diameter section creates a curved or bent path for the control rod as it enters the spider finger, allowing lateral deflection through a controlled geometric transition rather than a sharp angle. This curved geometry distributes stresses more evenly and prevents concentration at the joint interface.
Data Source
AI summary
A rod cluster control assembly having a control rod upper end plug formed in two parts and connected together with a flexible joint coupling located at or below a connecting finger on a spider vane. The upper portion of the upper control rod end plug is screwed into the connecting finger on the spider vane and lock welded between a lower portion of the finger and a shoulder on an abutting ledge of the upper portion of the end plug.