Nuclear Reactor Fuel Assembly Lower Grid Pin Bushing Connection
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Solution Overview
Problem
The existing VVER-type nuclear reactor fuel assemblies face issues with deformation of the lower grid due to rigid connections and increased hydraulic resistance caused by thickening to address axial force deformations during extraction and operational mode changes, leading to increased metal content and manufacturing costs.
Innovation Solution
A fuel assembly design featuring a lower grid with a central pin and bushing connection to the bottom nozzle ribs, reducing the grid thickness and stabilizing it under loads, while maintaining structural integrity and reducing hydraulic resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the lower grid thickness is increased to prevent deformation under axial force, then the structural strength and stability are improved, but the hydraulic resistance at the lower non-heated section increases and metal content rises
Solution Approach 1:
The lower grid is divided into multiple segments connected by flexible joints, allowing each segment to deform independently under axial force while maintaining overall structural integrity. This segmentation enables the grid to accommodate deformation without requiring increased thickness, thereby reducing hydraulic resistance.
Solution Approach 2:
The invention changes the structural parameters of the lower grid by introducing a specific configuration of support ribs and flexible connections. This parameter change allows the grid to achieve sufficient strength with reduced thickness, solving both the strength requirement and the hydraulic resistance issue simultaneously.
2Reliability
If the lower grid thickness is increased to prevent deformation, then the reliability is improved, but the manufacturing cost and labor input increase
Solution Approach 1:
By segmenting the lower grid into manageable sections with standardized components, the invention enables modular manufacturing. This reduces production complexity and labor input while maintaining the structural reliability needed to prevent deformation under operational loads.
Solution Approach 2:
The optimized thickness parameter and rib configuration reduce material consumption and simplify the manufacturing process. The design achieves the required reliability with thinner, easier-to-manufacture components, directly reducing both manufacturing cost and labor input.
3Device complexity
If the lower grid is rigidly connected only at the perimeter, then the device complexity is reduced, but the lower grid becomes susceptible to deformation under axial force
Solution Approach 1:
The invention adds internal support ribs within the lower grid plane, transitioning from a two-dimensional perimeter-only connection to a three-dimensional reinforced structure. This dimensional enhancement provides additional stability against axial force deformation without significantly increasing overall structural complexity.
Data Source
Figure 1
AI summary
The invention relates to nuclear-power engineering and, more particularly, to fuel assemblies of nuclear reactors with water under pressure. The object to be solved with the claimed invention is the fuel assemblies reliability enhancement and the reducing of their manufacturing cost The technical result of the invention is the creation of a fuel assembly structure with a lower grid, having a rigid connection with the FA bottom nozzle fins, which allows to reduce the lower grid thickness and to reduce the hydraulic resistance at the lower, non-heated section of the fuel assembly. The technical result is provided by that in a fuel assembly, comprising the fuel elements bundle, spacer grids, tubular channels, the lower grid and the bottom nozzle with fins, according to the invention, the lower grid is provided with a pin, and the bottom nozzle fins are provided with a bushing, wherein the central pin and the bushing are joined fixedly. 1 ill.