Fuel Rod End Plug Geometry for Reliable Resistance Pressure Welding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing resistance welding methods for nuclear reactor fuel rod tube end plugs face challenges such as weld failures due to material incompatibilities, especially with high-temperature reactors, and AC welding's inefficiencies, leading to poor bond quality and stress concentrations.
Innovation Solution
A fuel rod design with annular end faces of equal surface area and a continuous, curved undercut in the tube end plug minimizes stress concentrations, combined with a resistance pressure weld using direct current for controlled heating and bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If resistance welding is used to connect tube end plugs to cladding tubes, then welding speed and productivity are improved, but weld reliability deteriorates due to material incompatibilities and temperature differentials
Solution Approach 1:
The patent changes the electrical parameter from AC to DC welding current, and controls the temporal sequence of heating and pressing phases. DC current provides sustained heating without cooling cycles, while the separated heating-pressing sequence allows temperature equalization before bonding, resolving the reliability issue while maintaining productivity
Solution Approach 2:
The patent applies preliminary heating to equalize temperatures between the tube end plug and cladding tube before applying pressing force. This preliminary thermal preparation eliminates temperature differentials that cause stress concentrations, ensuring reliable welds while maintaining efficient processing
2Device complexity
If AC welding current is used, then equipment simplicity is improved, but welding quality deteriorates due to heating and cooling cycles causing stress concentrations
Solution Approach 1:
The patent changes the electrical parameter from AC to DC current. DC current provides continuous unidirectional heating without the heating-cooling cycles inherent in AC welding, eliminating the repeated thermal stress that degrades weld quality. This parameter change maintains equipment simplicity while dramatically improving manufacturing precision
3Temperature
If tube end plug mass is increased to match cladding tube mass, then temperature uniformity is improved, but stress concentrations increase due to sharp angular transitions in recess geometry
Solution Approach 1:
The patent replaces sharp angular transitions with continuously curved surfaces in the tube end plug recess geometry. Curved transitions eliminate stress concentration points while maintaining the mass matching needed for temperature uniformity during welding, thereby preserving both thermal uniformity and structural strength
4Reliability
If heating time is extended to improve bond quality, then welding reliability is improved, but productivity deteriorates due to increased cooling periods in AC welding cycles
Solution Approach 1:
The patent changes from AC to DC current, eliminating the periodic cooling phases inherent in AC cycles. DC current provides continuous heating that maintains elevated temperature for extended periods without interruption, allowing thorough bonding while preventing heat loss. This resolves the contradiction by enabling long heating times without productivity penalty
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
This design enhances weld quality and strength, reducing failures and ensuring a reliable seal, even in high-temperature environments, by uniformly heating and bonding the cladding tube and end plug.
Implementation Method 1
a controlled high current, typically alternating current (AC), is passed between the cladding tube 4 and the end plug 6 which is compressively loaded. Resistance at the interface between the end plug 6 and the cladding tube 4 generates localized heating resulting in a diffusion bond
Implementation Method 2
Resistance at the interface between the end plug 6 and the cladding tube 4 generates localized heating resulting in a diffusion bond
Data Source
AI summary
A fuel rod for a nuclear reactor, including a cladding tube having a first end with an annular end face, a second end with an annular end face, and a cylindrical body portion extending therebetween, and a first tube end plug including a front portion, an annular lip with an annular end face, and a substantially straight cylindrical body portion extending therebetween, wherein the surface area of the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are substantially equal, and the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are connected by a resistance pressure weld.