Nuclear Fuel Grid Cell Stiffness and Flow Design
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Solution Overview
Problem
Existing tube grid cell designs for nuclear fuel bundles in reactors lack improved lateral properties and stiffness while also experiencing high hydraulic resistance, which affects the stability and efficiency of fuel rod spacing and coolant flow.
Innovation Solution
A tube grid cell with a circular cross-section, featuring a leaf spring and two pairs of horizontal support members positioned 120 degrees apart, providing a five-point contact system for improved stiffness and reduced hydraulic resistance, and a grid assembly with triangular or square pitch between fuel rods to minimize impact and enhance lateral spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional ferrule designs with discrete cylinders and springs are used, then fuel rod spacing is maintained, but lateral properties and grid assembly stiffness are insufficient
Solution Approach 1:
The tube grid cell is divided into distinct functional segments: upper and lower solid sections for structural stiffness, and a middle section with support members for fuel rod positioning. This segmentation allows each part to optimize its function while contributing to overall assembly performance.
Solution Approach 2:
The tube grid cell combines different material properties within a single integrated structure - solid sections provide rigidity while the middle section with spring elements provides flexibility and positioning capability. This composite approach resolves the contradiction between stiffness and spacing stability.
2Strength
If solid housing sections are added to improve lateral properties, then grid assembly stiffness increases, but hydraulic resistance increases due to blockage
Solution Approach 1:
The housing is designed with spatially varying properties: solid sections at the top and bottom for lateral stiffness, and an open middle section for fluid flow. This local differentiation allows the structure to provide stiffness where needed while minimizing hydraulic resistance in the coolant flow path.
Solution Approach 2:
The support members are arranged in three-dimensional space with specific spacing and orientation, creating a configuration that provides lateral support while maintaining flow channels. The vertical arrangement of solid sections at extremes allows coolant to flow through the middle section with minimal obstruction.
3Reliability
If support members are positioned to provide five-point contact, then fuel rod support stability improves, but manufacturing complexity increases
Solution Approach 1:
Multiple support members are integrated into a single tube grid cell structure rather than being separate components. This merging reduces the number of parts and assembly steps while achieving the five-point contact configuration for stable fuel rod support.
Solution Approach 2:
The support members serve multiple functions: providing lateral positioning, axial support, and vibration damping through spring elements. This multi-functionality reduces the need for additional specialized components, simplifying manufacturing.
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 design enhances lateral properties and stiffness of the grid assembly, reducing hydraulic resistance and improving thermal hydraulic characteristics by minimizing blockage and providing a stable five-point contact system for fuel rod support.
Implementation Method 1
one leaf spring and two pairs of support members... providing a five point contact system to support the fuel rod
Data Source
AI summary
A tube grid cell (2) for a fuel bundle (8) of a nuclear reactor. The tube grid cell (2) having the length (L), comprises a cell housing (10) which has, along the longitudinal axis A, a lower section (16), an upper section (18) and a middle section (20). The middle section (20) is provided with two pairs of support members (22) and a resilient member (24) configured to generate a resilient force in an inward radial direction, the resilient member is arranged at essentially equal distance from the support members (22), and positioned approximately (120) degrees apart from the support members seen along axis A. The upper section (18) and the lower section (16) have respectively a length L1 and L2 along axis A that is larger than 0.1 L and smaller than 0.3 L, and is provided with a solid housing wall, having an even thickness and no openings, indentations or protrusions.