Nuclear Fuel Assembly Hold-Down Spring Unit Design

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Solution Overview

Problem

Conventional hold-down spring units for nuclear fuel assemblies apply excessive resistance force under hot full power conditions, compromising the mechanical and structural stability of the assemblies.

Innovation Solution

A hold-down spring unit is designed with a first spring providing hold-down force under both start-up and hot full power conditions, and a second spring providing additional force only under start-up conditions, minimizing hold-down margin and optimizing resistance to maintain stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional hold-down spring unit applies sufficient hold-down force under start-up conditions, then the nuclear fuel assembly is stabilized during assembly, but excessive resistance force is applied under hot full power conditions, compromising mechanical and structural stability

Engineering Contradiction:

Improvehold-down performanceVSAvoidmechanical and structural stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The hold-down spring unit is divided into multiple independent springs (first spring, second spring, third spring) arranged in parallel. Each spring can be independently designed with different characteristics, allowing the system to provide appropriate hold-down force under different operating conditions without compromising structural stability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs springs with different wire diameters, mean diameters, and active coil numbers to create varying spring constants. The first spring has a larger wire diameter and smaller mean diameter for higher stiffness, while the second and third springs have smaller wire diameters and larger mean diameters for lower stiffness, enabling parameter optimization for different operational phases

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If a single spring design is used to provide hold-down force, then the structure is simple, but it cannot optimize resistance force for different operational conditions (start-up vs. hot full power)

Engineering Contradiction:

Improvespring unit structureVSAvoidadaptability to operational conditions

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The multi-spring configuration enables the hold-down spring unit to perform multiple functions: providing primary hold-down force during assembly, distributing load under partial power conditions, and sharing the resistance force burden under hot full power conditions, thereby adapting to various operational requirements

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces excessive resistance force during hot full power operations, ensuring stable positioning and enhanced mechanical and structural stability of the nuclear fuel assembly by adjusting hold-down force according to operational conditions.

Implementation Method 1

a first spring providing a hold-down force upon the nuclear fuel assembly under start-up conditions and hot full power conditions of a nuclear reactor

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

a second spring providing an additional hold-down force upon the nuclear fuel assembly only under start-up conditions of the nuclear reactor

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS8483348B2Method of providing a hold-down force upon a nuclear fuel assembly

Publication Date: 2013.07.09 KEPCO NUCLEAR FUEL CO LTD

AI summary

A hold-down spring unit for a top nozzle of a nuclear fuel assembly. The hold-down spring unit is coupled to the upper end of the top nozzle of the nuclear fuel assembly. The hold-down spring unit includes a first spring which provides a hold-down force upon the nuclear fuel assembly under start-up conditions or hot full power conditions of a nuclear reactor, and a second spring which provides an additional hold-down force upon the nuclear fuel assembly under start-up conditions of the nuclear reactor. The hold-down margin under start-up conditions or hot full power conditions is reduced, thus enhancing the mechanical and structural stability of the nuclear fuel assembly.