Dual Chamfer Nuclear Fuel Pellet Design for Chipping Prevention

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Solution Overview

Problem

Sintered fuel pellets in nuclear reactors are prone to chipping during manufacturing and handling, leading to defects that cause hot spots, mechanical stress on cladding, and potential cladding failure, resulting in radioactive leaks due to the formation of sharp edges and missing pellet surfaces.

Innovation Solution

A sintered fuel pellet design featuring a first chamfer with a steep slope (7°-40°) and a second chamfer with a gentle slope (0.2°-10°) to prevent sharp edges and ensure a soft contact between pellets, reducing the risk of chipping and mechanical stress on the cladding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a single chamfer is provided on the fuel pellet end face, then the loading ease is improved, but chipping risk remains

Engineering Contradiction:

Improveloading easeVSAvoidchipping risk

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The single chamfer is segmented into two distinct chamfers: a first chamfer with a first slope and a second chamfer with a second slope. This segmentation allows each chamfer to serve a specific function - the first chamfer facilitates loading while the second chamfer prevents chipping by avoiding sharp edges, thus resolving the contradiction between loading ease and chipping risk.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different slopes are assigned to different chamfers based on their specific functions. The first chamfer has a steeper slope optimized for loading, while the second chamfer has a gentler slope optimized for preventing chipping. This local differentiation of geometric properties allows simultaneous optimization of loading ease and chipping prevention.

Inventive Principle:

Principle #3Local quality

2Ease of operation

If a chamfer is provided to ease loading, then loading ease is improved, but sharp edges form causing chipping

Engineering Contradiction:

Improveloading easeVSAvoidsharp edges

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The potential harm of sharp edges is converted into a benefit by introducing the second chamfer with a gentle slope. This second chamfer specifically targets the sharp edge problem at the interface between the first chamfer and the pellet body, transforming the harmful sharp edge into a beneficial rounded transition that prevents chipping while maintaining loading ease.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Ease of manufacture

If chipping occurs during manufacturing, then manufacturing complexity increases, but pellet defects increase

Engineering Contradiction:

Improvemanufacturing complexityVSAvoidpellet defect rate

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The dual chamfer geometry is designed into the mold before manufacturing. By pre-configuring the mold with the specific dual-chamfer geometry, the pellet is formed with the correct shape during manufacturing, eliminating the need for post-manufacturing corrections and reducing defect rates while maintaining manufacturing simplicity.

Inventive Principle:

Principle #10Preliminary action

4Strength

If missing pellet surface occurs due to chipping, then cladding mechanical stress increases, but safety decreases

Engineering Contradiction:

Improvecladding supportVSAvoidcladding failure risk

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The second chamfer with its gentle slope is designed in advance to prevent the formation of sharp edges that cause chipping. By preventing chipping before it occurs, the design eliminates the subsequent harmful effects including missing pellet surface, reduced cladding support, and increased cladding failure risk, thus addressing the contradiction between strength and reliability.

Inventive Principle:

Principle #9Preliminary anti-action

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 dual chamfer design significantly reduces the risk of chipping and cladding failure, maintaining a soft contact between pellets and preventing radioactive leaks, while ensuring a conventional shape with reduced surface defects and improved reactor efficiency.

Implementation Method 1

A fuel pellet is obtained by sintering of a green fuel pellet mainly made from uranium oxide

Methodology Applied

Scientific EffectSintering: Sintering

Data Source

PatentUS9042507B2Nuclear reactor green and sintered fuel pellets, corresponding fuel rod and fuel assembly

Publication Date: 2015.05.26 AREVA NP SAS

AI summary

A sintered fuel pellet for a water nuclear reactor fuel rod including a peripheral wall extending along a central axis and two end faces. At least one of the end faces includes at least a first chamfer extending from the peripheral wall towards the central axis with a first non-zero slope with respect to a plane perpendicular to the central axis and a second chamfer extending from the first chamfer towards the central axis with a second non-zero slope with respect to a plane perpendicular to the central axis, wherein the first slope is different from the second slope.