Nuclear Fuel Rod Plenum Spring Assembly Spacer Design
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Solution Overview
Problem
Conventional nuclear reactor fuel rod designs experience nonuniform pressure distribution on the top surface of fuel pellets due to the limited contact area of the plenum spring, leading to potential pellet chipping and vibration, and pose challenges in installation and performance.
Innovation Solution
A threaded spacer is introduced between the plenum spring and the top pellet to distribute pressure uniformly and prevent chip migration, featuring a flat head with a hex contour and spiral thread for secure attachment to the spring, ensuring proper pressurization and minimizing installation errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional plenum spring is used to hold fuel pellets in position, then the spring can apply pressure to the pellets, but the pressure distribution is nonuniform due to limited contact area, causing pellet chipping and vibration
Solution Approach 1:
A spacer is introduced as an intermediary component between the plenum spring and the fuel pellets. The spacer has a larger contact surface area than the spring, distributing the spring's force uniformly across the top surface of the pellets. This mediator resolves the contradiction by maintaining the necessary compressive force while eliminating the nonuniform pressure distribution that causes pellet damage and vibration.
2Device complexity
If the plenum spring directly contacts the top pellet surface, then the assembly is simple, but installation errors can occur and the spring may not properly pressurize the pellets
Solution Approach 1:
The spacer incorporates a hexagonal recess that receives a correspondingly shaped tool during installation, enabling self-alignment and self-correction of installation errors. The geometry of the spacer and tool interface guides proper positioning, making the assembly process self-correcting and highly reliable while maintaining simplicity.
3Volume of moving object
If the plenum spring has limited contact area with the pellets, then the spring structure is compact, but chip migration can occur from nonuniform pressure zones
Solution Approach 1:
The spacer serves as a mediator that distributes the spring's compact force over a larger area, eliminating nonuniform pressure zones that generate harmful effects. By placing the spacer between the compact spring and the pellets, the system maintains spring compactness while preventing pellet chipping and chip migration through uniform pressure distribution.
4Stability of the object's composition
If uniform pressure distribution is achieved on the pellets, then pellet stability improves, but the device complexity increases due to the additional spacer component
Solution Approach 1:
The system is segmented into distinct functional components: the plenum spring for applying force, the spacer for distributing pressure and providing alignment features, and the fuel pellets. This segmentation allows each component to perform its specific function optimally, achieving pellet stability through the spacer's pressure distribution while keeping the overall device relatively simple through clear functional division.
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 spacer design achieves uniform pressure distribution, reduces pellet chipping, and enhances fuel rod stability, facilitating correct assembly and preventing performance issues such as excessive clad corrosion and potential fuel melting.
Implementation Method 1
a spring extending between a top end plug and an upper surface of the active element, pressuring the active element toward a lower end plug
Implementation Method 2
A threaded spacer is introduced between the plenum spring and the top pellet to distribute pressure uniformly
Data Source
Figure 1
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AI summary
A nuclear fuel rod plenum spring assembly that has a spacer affixed to the lower end of the ground torsion spring. The spacer has a substantially flat surface on its underside that presses against the upper surface of the upper fuel pellets to spread the load of the spring over the top surface of the upper most fuel pellet.