Fuel Assembly End Plug Vibration Suppression
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Solution Overview
Problem
In fuel assemblies for boiling water reactors, the existing tie plate structures face issues with maintaining a constant binding force and preventing vibration of fuel rods, particularly due to differences in material properties between the tie plate and leaf springs, which can lead to loose parts and increased pressure loss.
Innovation Solution
A fuel assembly design featuring end plugs with support protrusions and closed-loop springs or cylindrical plates with protruding springs and support protrusions, which are integrated with the tie plate to provide lateral support and prevent vibration, ensuring the springs do not become loose parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If leaf springs are welded to the inner wall of the insertion hole in the upper tie plate, then vibration suppression of the fuel rod is improved, but the reliability deteriorates due to material incompatibility causing loose parts
Solution Approach 1:
The leaf spring and upper tie plate are formed as a single integrated component through stamping, eliminating the welded joint between dissimilar materials. This merging of components removes the source of loosening while maintaining the vibration suppression function through the integrated structure's elastic deformation capability.
Solution Approach 2:
The integrated upper tie plate and leaf spring are constructed from the same material (stainless steel), creating a homogeneous composite structure that avoids galvanic corrosion and differential thermal expansion issues between dissimilar materials like Inconel and stainless steel, thereby preventing loose parts.
2Productivity
If fuel rods are densely disposed in the reactor core, then the productivity is improved, but the harmful factors increase due to hydrodynamic vibration damage
Solution Approach 1:
The leaf spring acts as a flexible elastic element that deforms under hydrodynamic forces, absorbing vibration energy and providing continuous contact support to the fuel rod. This flexible mechanism effectively dampens hydrodynamic vibrations while allowing the dense fuel rod arrangement required for high productivity.
3Stability of the object's composition
If the binding force between tie plate and fuel component is maintained at constant level, then the stability is improved, but the device complexity increases to accommodate thermal expansion differences
Solution Approach 1:
The leaf spring transforms the rigid binding structure into a dynamic system that can elastically deform in response to thermal expansion and contraction. This dynamic capability allows the binding force to remain stable on average while accommodating instantaneous dimensional changes, without requiring complex adjustment mechanisms.
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 effectively suppresses fuel rod vibrations and reduces pressure loss by maintaining a stable support structure for the end plugs, even under varying conditions such as thermal expansion and water flow.
Implementation Method 1
a closed-loop spring having a portion that is inserted through an opening portion formed in the end plug and is stored in a single space formed in the end plug, and a remaining portion protruding to the outside of the end plug
Data Source
AI summary
A fuel assembly according to the present invention includes an end plug disposed on both upper and lower end portions of a fuel rod, and a tie plate that supports at least an upper portion of the end plug. The end plug includes a plurality of support protrusions on a surface of the end plug, and a closed-loop spring having a portion that is inserted through an opening portion formed in the end plug and is stored in a single space formed in the end plug, and a remaining portion protruding to the outside of the end plug. The end plug is supported by the plurality of support protrusions and the closed-loop spring in a state in which the plurality of support protrusions and the closed-loop spring are in contact with an inner wall of an insertion hole formed in the tie plate.