Nuclear Fuel Spacer Grid Vibration Reduction

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Solution Overview

Problem

Flow-induced high-frequency vibration in nuclear fuel assemblies causes fretting and damage to fuel rods due to turbulence in the coolant flow, which existing spacer grids fail to adequately address.

Innovation Solution

A spacer grid with elongated slots formed in the planar portions of the grid strips, independent of dimples or grid springs, to reduce vibration by modifying the surface structure and characteristics of the grid strips, allowing for various slot configurations without compromising structural strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional smooth grid strips are used in spacer grids, then manufacturing is simple and structural strength is maintained, but flow-induced high-frequency vibration causes fretting and damage to fuel rods

Engineering Contradiction:

Improvefuel rod protectionVSAvoidflow-induced vibration

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The grid strip surface is modified with local structures (protrusions and recesses) at specific locations rather than being uniformly smooth. These localized surface features create turbulence that reduces flow-induced vibration, while the overall grid structure maintains its strength and support function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The grid strip surfaces incorporate curved or rounded features (protrusions and recesses) instead of purely flat surfaces. These curved geometries disrupt the coolant flow pattern, reducing high-frequency vibration caused by flow-induced turbulence, while maintaining structural integrity.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Object-affected harmful factors

If grid strip surfaces are modified to reduce vibration, then flow-induced vibration is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improveflow-induced vibrationVSAvoidgrid strip fabrication

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The surface parameters of the grid strips are modified by adding protrusions and recesses with specific dimensional characteristics. These parameter changes create the necessary turbulence-reducing surface geometry while using standard manufacturing tolerances and processes to minimize fabrication complexity.

Inventive Principle:

Principle #35Parameter changes

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 modified spacer grid effectively reduces flow-induced high-frequency vibration, minimizing fretting and damage to fuel rods while maintaining structural integrity.

Implementation Method 1

Methodology Applied

Scientific EffectVibration reduction through surface structure modification:

Data Source

PatentUS9196386B2Spacer grid for nuclear fuel assembly for reducing high frequency vibration

Publication Date: 2015.11.24 KEPCO NUCLEAR FUEL CO LTD

AI summary

Disclosed herein is a spacer grid for a nuclear fuel assembly which is formed from grid strips of an improved structure, thus reducing flow-induced high-frequency vibration. The spacer grid has dimples or grid springs for supporting fuel rods and is formed from a plurality of grid strips assembled in a lattice shape to form lattice cells. Each of the grid strips has at least one slot formed in a planar portion of the grid strip separately from the dimple or grid spring. Therefore, characteristics of the vibration of the spacer grid can be set in a variety of different manners so that flow-induced high-frequency vibration can be reduced.