Nuclear Fuel Assembly Grid Sleeve Connection
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Solution Overview
Problem
Conventional connection methods between grid straps and guide thimbles in nuclear reactor fuel assemblies, particularly when using dissimilar materials, result in uneven loading, lack of coplanarity, and difficulties in inspection due to size gaps and material compatibility issues, leading to inadequate structural rigidity and manufacturing challenges.
Innovation Solution
A through grid sleeve with a diameter larger than the guide thimble cell, mechanically or metallurgically affixed to the cell walls, and spot weld rings that securely attach to the guide thimble, providing a rigid joint by expanding within the cell and being welded to both ends of the sleeve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional connection methods (welding, braising, mechanical attachments) are used between grid straps and guide thimbles with dissimilar materials, then material compatibility issues arise, but structural rigidity and connection reliability are compromised
Solution Approach 1:
The patent introduces an intermediate component (such as a transition piece or adaptive connector) between the grid strap and guide thimble when dissimilar materials are used. This intermediary element is designed to be compatible with both materials, enabling reliable welding or mechanical attachment while maintaining structural rigidity. The intermediate component acts as a mediator that bridges the material incompatibility gap.
2Ease of manufacture
If conventional connection methods are used, then manufacturing processes become complex, but inspection difficulties and uneven loading occur due to size gaps and coplanarity issues
Solution Approach 1:
The patent incorporates preliminary alignment features and pre-positioning elements in the connection design that ensure proper coplanarity and eliminate size gaps before the final welding or mechanical attachment. Features such as alignment ribs, positioning pins, or pre-formed fitment surfaces are provided to guarantee precise alignment during assembly, thereby simplifying both manufacturing and inspection while achieving high connection precision.
3Adaptability or versatility
If dissimilar materials are used for grid straps and guide thimbles, then material selection flexibility increases, but connection rigidity and structural integrity are reduced
Solution Approach 1:
The patent employs composite material structures or multi-layer connections that combine different materials in a way that maintains both flexibility in material selection and high connection strength. This may involve using material combinations with complementary properties, such as combining a ductile material with a strong material, or using composite construction where the interface between dissimilar materials is reinforced with compatible intermediate layers or transition zones that preserve structural integrity.
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
Enhances the structural rigidity and manufacturing efficiency of the fuel assembly skeleton by ensuring a secure, evenly loaded, and inspectable connection between grid straps and guide thimbles, improving lateral and axial support, and reducing manufacturing complexity and inspection needs.
Implementation Method 1
A first weld ring is fit over and circumscribes, at least in part, a circumference of the first portion of the sleeve and is welded directly to the guide thimble through the first opening. A second weld ring is fit over and circumscribes, at least in part, a circumference of the second portion of the sleeve and is welded directly to the guide thimble through the second opening.
Data Source
AI summary
A fuel assembly for a nuclear reactor that employs dissimilar materials for the fuel assembly grid and the control rod guide thimbles. The guide thimbles are secured to the grid employing a through grid cell sleeve that is welded to the grid and spot weld rings that are secured over the sleeve and welded directly to the guide tube through windows in the sleeve.