Helical Support Grid for Nuclear Fuel Assembly
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Solution Overview
Problem
Conventional support grid designs for nuclear fuel assemblies are complex to assemble and can cause fretting between the grids and fuel rods, leading to potential nuclear contamination due to vibrations and pressure drops, which complicates water flow and increases the risk of fuel rod cladding breach.
Innovation Solution
A support grid with a frame assembly featuring helical tubular members that have varying diameters and helical fuel rod contact portions, eliminating the need for mixing vanes and allowing for easier assembly, reducing torque and pressure drops, and minimizing fretting by distributing load effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional support grid designs with interleaved straps, springs, and dimples are used to support fuel rods, then the fuel rods can be positioned and supported at multiple points, but the assembly process becomes time-consuming and complex
Solution Approach 1:
The support grid is divided into modular cells, each containing a tubular member with integrated spring and dimple features. This segmentation allows for standardized manufacturing and easier assembly while maintaining the six-point support function for each fuel rod.
Solution Approach 2:
The spring and dimple features are merged into a single integrated tubular member structure rather than being separate components. This merging simplifies the assembly process by reducing the number of parts that need to be manually positioned and assembled, while still providing the necessary support functions.
2Use of energy by moving object
If mixing vanes are added to the support grid to facilitate water mixing and promote convective heat exchange, then heat transfer efficiency improves, but torque and pressure drops increase and assembly complexity increases
Solution Approach 1:
The tubular members are designed to serve multiple functions: supporting the fuel rod, providing mixing action through their helical configuration, and maintaining structural integrity. This multi-functionality eliminates the need for separate mixing vanes, reducing overall device complexity while achieving the same heat transfer enhancement.
Solution Approach 2:
The mixing function is extracted from separate mixing vane components and integrated directly into the tubular support members themselves. This extraction eliminates the need for additional mixing components, reducing assembly complexity and torque while maintaining the convective heat exchange benefits.
3Reliability
If conventional flat strap members with springs and dimples are used to form grid cells, then fuel rods can be supported at six points per cell, but the assembly process requires precise positioning and becomes time-consuming
Solution Approach 1:
The spring and dimple features are pre-positioned and integrated into the tubular members during manufacturing rather than being assembled separately. This preliminary action ensures precise positioning of the support points while eliminating the time-consuming manual positioning required in conventional assembly processes.
Solution Approach 2:
The tubular members are designed to self-align and self-position during assembly through their integrated spring and dimple features, reducing the need for precise manual positioning. The springs provide automatic adjustment and the dimples guide the fuel rod into the correct position, enabling faster assembly while maintaining support precision.
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 solution simplifies the assembly process, reduces fretting wear, maintains efficient water mixing, and minimizes the risk of nuclear contamination by providing a stable and efficient support system for fuel rods.
Implementation Method 1
The springs must be disposed opposite the dimples so that the fuel rod is biased against the dimples by the springs. The springs and dimples of each cell engage the respective fuel rod extending through the cell thereby supporting the fuel rod at six points
Implementation Method 2
The tubular member has at least one helical fluted portion or fuel rod contact portion
Data Source
AI summary
A support grid for a nuclear fuel assembly, the nuclear fuel assembly including a generally cylindrical fuel rod with a diameter, wherein the support grid includes a frame assembly having a plurality of generally circular cells and a plurality of helical frame members. The helical frame members are disposed in the cells and are structured to contact the cell as well as a fuel rod. The helical fuel rod contact portion may have a variable pitch.