Angled Edge Grid Straps for Vortex Shedding Control
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Solution Overview
Problem
Conventional nuclear reactor fuel assemblies experience resonant vibration of grid straps due to vortex shedding lock-in, leading to fretting of fuel rod cladding and potential breaches, as well as fatigue and cracking of grid straps, which can result in the release of radioactive materials.
Innovation Solution
The design incorporates grid straps with angled trailing and leading edges to break the correlation of vortices, employing saw tooth or curved patterns to vary the phase of vortex shedding, thereby canceling delta pressure oscillations and preventing uniform oscillating forces that cause vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional grid straps with straight edges are used, then manufacturing is simple, but vortex shedding lock-in occurs causing resonant vibration and potential failure
Solution Approach 1:
The grid strap edges are designed with asymmetric angular contours instead of straight edges. The leading and trailing edges are angled at different orientations relative to the flow direction, creating asymmetric vortex shedding patterns that prevent lock-in resonance. This asymmetric geometry breaks the correlation between vortices shed from different edges, eliminating the resonant vibration condition while maintaining manufacturing feasibility through standard angular fabrication techniques.
Solution Approach 2:
The grid strap edges incorporate curved or rounded contours instead of sharp angular edges. By rounding the trailing and leading edges, the patent modifies the vortex shedding characteristics to prevent coherent vortex formation. The curved edges disrupt the flow separation points and eliminate the sharp corners that would otherwise generate correlated vortices, thereby preventing resonant vibration while remaining manufacturable.
2Reliability
If grid straps with angled edges are used to break vortex correlation, then vibration is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies angular contour parameters within ranges rather than requiring exact precise values. The leading and trailing edges are defined with angular orientations that fall within acceptable tolerance ranges (e.g., 10-45 degrees from perpendicular), allowing manufacturers to produce the vibration-reducing effect without requiring ultra-precise angular control. This parameter approach maintains reliability while accommodating standard manufacturing tolerances.
3Ease of manufacture
If straight edges are used on grid straps, then manufacturing is easier, but fretting of fuel rod cladding occurs due to vibration
Solution Approach 1:
By incorporating asymmetric angular contours on the grid strap edges, the patent eliminates the resonant vibration that causes fretting damage to fuel rod cladding. The asymmetric geometry prevents vortex shedding lock-in, thereby removing the primary mechanism that leads to cladding fretting while maintaining ease of manufacture through standard angular shaping techniques.
Solution Approach 2:
Rounding the grid strap edges eliminates sharp corners that generate correlated vortices and resonant vibration. This curved edge design prevents the vibration-induced fretting of fuel rod cladding while remaining straightforward to manufacture using standard rounding or filleting operations.
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
This design effectively reduces grid strap vibration, minimizing the risk of fuel rod cladding breaches and grid strap damage, thereby enhancing the safety and integrity of the nuclear fuel assembly by preventing resonance-induced failures.
Implementation Method 1
resonant vibration of the grid straps which results from vortex shedding lock-in vibration when the shedding frequency is close to the natural frequency of the strap
Implementation Method 2
either one or both the leading edge or the trailing edge is provided with an angled contour that varies the elevation of either or both the leading edge or the trailing edge... the angled contour... break the correlation of the vortices... vary the phase of vortex shedding... canceling delta pressure oscillations
Data Source
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AI summary
A nuclear fuel assembly support grid formed from an array of a plurality of orthogonally arranged straps in an egg-crate configuration with angled trailing and/or leading edges that are designed to break the correlation of vortices shed from the edges of the grid straps by varying the phase of the vortices to avoid resonant vibration of the straps.