Nuclear Fuel Rod End Plug Resistance Welding
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Solution Overview
Problem
Resistance welding of end plugs to nuclear fuel rod cladding tubes is limited by non-destructive examination feasibility, susceptibility to contaminants, and the need for post-weld mechanical removal of weld upset, complicating the process.
Innovation Solution
A method involving an end plug with a cylindrical bond portion and a cladding seat of reduced diameter, where electrical current is applied while clamping to generate a resistance weld, allowing for a self-cleaning process with controlled sliding and potential non-destructive examination of the weld bond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If resistance welding is used to join end plugs to cladding tubes, then welding speed and productivity are improved, but non-destructive examination becomes infeasible and weld quality is susceptible to undetected contaminants
Solution Approach 1:
The end plug is divided into distinct functional segments: a cladding seat portion that contacts the cladding tube, a bond portion that forms the weld, and a main body portion. This segmentation allows the bond portion to be specifically optimized for weldability and examination accessibility, while the cladding seat provides stable contact. The separated functional zones enable the weld to be positioned where it can be properly examined while maintaining high welding speed.
Solution Approach 2:
The cladding seat acts as an intermediary element between the end plug and the cladding tube. It provides a dedicated contact surface that ensures proper positioning and electrical contact for resistance welding, while the bond portion serves as an intermediary zone that facilitates the actual welding process and enables examination. This intermediary structure resolves the contradiction by separating the contact function from the welding function.
2Productivity
If high current is applied during resistance welding to generate sufficient heat, then welding speed is improved, but weld upset increases requiring mechanical removal or suppression
Solution Approach 1:
The end plug features localized geometric variations with different diameters at different sections. The bond portion has a specific diameter that is optimized for weldability and controlled heat generation, while the cladding seat has a different diameter optimized for contact stability. This local quality differentiation allows high current to be applied without excessive upset, as the heat is concentrated in the bond portion rather than distributed throughout the entire end plug.
Solution Approach 2:
The invention changes geometric parameters of the end plug, specifically the diameters of the cladding seat and bond portion. By optimizing these dimensional parameters, the resistance welding process generates sufficient heat at controlled locations without producing excessive weld upset. The parameter optimization allows high welding speed while minimizing harmful effects.
3Strength
If the cladding tube is forced over the end plug during welding, then a strong bond is achieved, but the process becomes more complex requiring precise control of slide distance
Solution Approach 1:
The end plug is pre-formed with specific geometric features including a cladding seat with reduced diameter and a bond portion with optimized dimensions. These preliminary geometric preparations ensure that when the cladding tube is forced over the end plug, the sliding distance is naturally controlled by the geometric transitions. The preliminary shaping of the end plug eliminates the need for complex real-time control mechanisms.
Solution Approach 2:
The geometric design of the end plug, with its stepped configuration and optimized bond portion dimensions, provides built-in control that cushions against process variability. The natural stops created by the geometric transitions ensure consistent weld quality without requiring complex active control systems.
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 method provides a strong, self-cleaning weld with controlled bond length and quality, enabling non-destructive examination and reducing post-weld processing needs, enhancing robustness and reliability.
Implementation Method 1
a high current is passed between the cladding and the end plug which is compressively loaded. Resistance at the interface between the end plug and the cladding generates localized heating resulting in a diffusion bond
Data Source
AI summary
An open end of a cladding tube of a nuclear fuel rod is plugged with an end plug having a main body and a cylindrical bond portion extending from the main body and terminating in a cladding seat with reduced diameter compared with the cylindrical bond portion. The plugging includes clamping the open end of the cladding tube against the cladding seat of the end plug and, while clamping, applying electrical current between the end plug and the open end of the cladding tube so as to force the open end of the cladding tube over the cladding seat and slide over the cylindrical bond portion of the end plug and to generate a resistance weld between a cylindrical bonding surface of the cylindrical bond portion of the end plug and the inside surface of the open end of the cladding tube.