Elastic Holding Device for Nuclear Fuel Plate Swelling
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Solution Overview
Problem
Current fuel plate holding systems for fast-flow nuclear reactors face challenges in accommodating differential expansion and swelling, leading to mechanical stress and potential degradation of fuel elements, while also requiring a high volume fraction of fuel and efficient cooling in severe thermal gradients.
Innovation Solution
A holding device with a cage-like structure that mechanically decouples fuel plates from each other and their support structures, using isostatic connections and elastic retaining mechanisms to allow free deformation and minimize interaction stresses, while maintaining a high volume fraction of fuel and ensuring efficient gas circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If fuel plates are rigidly held in support structures to maintain geometric stability, then structural integrity is improved, but mechanical stress and degradation of fuel elements occur due to differential expansion and swelling
Solution Approach 1:
The support structure is segmented into multiple independent holding devices distributed along the fuel plate, rather than a single rigid support. Each holding device independently supports the plate, allowing local deformation without transmitting stress across the entire structure. This segmentation decouples the mechanical constraints and enables the fuel plate to expand and swell freely while maintaining overall geometric stability.
Solution Approach 2:
The holding devices are designed with specific geometric parameters that provide just enough constraint to maintain stability while allowing sufficient freedom for thermal expansion. The spacing, orientation, and geometry of the holding devices are optimized to permit differential expansion in the thickness direction while preventing excessive displacement, thus resolving the contradiction between stability and stress prevention.
2Manufacturing precision
If fuel plates are held firmly to maintain positioning accuracy, then positioning stability is improved, but interaction stresses increase leading to fuel element degradation
Solution Approach 1:
The positioning function is segmented into multiple independent holding devices rather than a single rigid positioning system. Each device provides localized positioning constraint, maintaining accuracy for individual plates while allowing independent movement. This eliminates the transmission of interaction stresses through a unified rigid support structure.
Solution Approach 2:
The holding devices act as intermediary elements between the fuel plates and the support structure. They provide necessary positioning constraints while serving as mechanical cushions that prevent direct rigid contact and stress transmission between the fuel plates and the support structure, thus reducing harmful interaction stresses.
3Strength
If support structures are made rigid to ensure mechanical architecture, then structural strength is improved, but volume fraction of fuel decreases due to larger structure size
Solution Approach 1:
The support structure is divided into multiple small, distributed holding devices rather than a single large rigid structure. Each holding device is minimized in size while collectively providing the necessary mechanical architecture strength. This segmentation reduces the total volume of support structure, thereby increasing the fuel volume fraction.
Solution Approach 2:
The holding devices are strategically positioned at critical locations where mechanical support is most needed, rather than providing uniform rigid support throughout. This localized approach provides sufficient structural strength at key positions while minimizing the overall volume of support structure, maximizing the fuel volume fraction.
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 enables the fuel plates to deform freely without significant interaction stresses, maintaining a high fuel volume fraction and facilitating efficient cooling, thus enhancing the mechanical integrity and operational efficiency of the reactor core.
Implementation Method 1
each upper holding means providing elastic holding of an upper longitudinal end of a plate in a direction of the width of the plate and allowing free deformation of the upper longitudinal end of the plate in a direction of the thickness of the plate
Implementation Method 2
The heat transfer fluid, for example helium, circulates between the plates ensuring the extraction of calories by heat exchange
Implementation Method 3
the fuel elements, which are the heating elements, are at a higher temperature than their support structures, which leads to a positive differential thermal expansion of the fuel elements with respect to their holding structure
Implementation Method 4
the fast spectrum introduces differential swelling phenomena in addition to differential expansions. By swelling is meant a definitive deformation of the materials
Data Source
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AI summary
The invention relates to a device for holding nuclear fuel plates (4) having a longitudinal axis (X), that comprises a bottom (6) defining a lower longitudinal end of the holding device and a lid (8) defining an upper longitudinal end of the holding device, the bottom (6) and the lid (8) being rigidly connected together, a plurality of upper holding means (18) for the plates (4) and connected to the lid (8) and a plurality of lower holding means (16) for the plates (4) and connected to the bottom (6) for elastically holding the longitudinal ends of the plates (4) in the width (R) direction of the plate (4) and for allowing the free deformation of said longitudinal ends in the thickness (T) direction of the plate.