Trapezoidal Nuclear Fuel Pellet Sintering Without Grinding
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Solution Overview
Problem
Conventional methods for manufacturing annular nuclear fuel pellets face challenges in achieving precise inner and outer diameter tolerances due to sintering deformation and non-uniform green density distribution, leading to heat flux asymmetry and increased safety risks in nuclear fuel rods.
Innovation Solution
A method involving single action uni-axial pressing with an inclined wall-type forming mold to create a trapezoidal annular green compact, which is then sintered under a reducing gas atmosphere, resulting in a pellet with diametric tolerances of 13 μm or less without the need for grinding, and maintaining uniform diameters along the height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional double action uni-axial pressing is used to manufacture annular green compact, then manufacturing process is simple, but sintering deformation occurs causing large diametric tolerances
Solution Approach 1:
The patent applies asymmetry by using an inclined wall-type forming mold where the inner wall is inclined at a specific angle (α) relative to the central axis, creating a trapezoidal green compact shape. This asymmetric geometry compensates for sintering shrinkage, resulting in a cylindrical pellet with uniform diameter and tolerance of 13 μm or less after sintering, eliminating the need for grinding processes.
2Manufacturing precision
If non-uniform green density distribution is present in the green compact, then pressing process is easier, but sintering deformation occurs causing diameter variation along height
Solution Approach 1:
The patent applies local quality by creating a green compact with non-uniform density distribution through the inclined wall forming process. The varying pressure distribution during pressing creates higher density in certain regions, which compensates for sintering shrinkage in a controlled manner, resulting in uniform diameter along the pellet height after sintering.
3Reliability
If conventional manufacturing method is used, then production cost is lower, but heat flux asymmetry occurs reducing safety margin
Solution Approach 1:
The patent applies preliminary action by pre-shaping the green compact with a trapezoidal cross-section using the inclined wall forming mold before sintering. This preliminary geometric configuration compensates for sintering shrinkage, ensuring uniform diameter and reducing heat flux asymmetry in the final pellet, thereby improving safety margin without requiring subsequent grinding operations.
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 approach allows for precise control of inner and outer diameters, reducing heat flux asymmetry and enhancing safety by minimizing diametric tolerances, thereby improving the thermal margin and reducing the need for costly grinding processes.
Implementation Method 1
sintering the annular nuclear fuel green compact under a reducing gas atmosphere to obtain the annular nuclear fuel pellet
Implementation Method 2
sintering the annular nuclear fuel green compact under a reducing gas atmosphere
Data Source
AI summary
A method for manufacturing an annular nuclear fuel pellet is provided. In the method, an annular nuclear fuel green compact whose lateral cross-section is a trapezoid is prepared. The thickness of the annular nuclear fuel green compact reduces along one direction of the central axis, and a green density of the nuclear fuel green compact increases along one direction of the central axis. The annular nuclear fuel green compact is sintered under a reducing gas atmosphere so that the annular nuclear fuel pellet is obtained. According to this method, the annular pellet which has uniform inner and outer diameters and small diametric tolerances along the pellet height is fabricated without grinding the pellet surfaces.