Nuclear Fuel Rod Spacer Grid Strip With Cantilevered Spring Tab
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Solution Overview
Problem
Existing nuclear fuel assembly spacer grids face challenges in minimizing flow resistance while maintaining suitable support for fuel rods and ensuring good manufacturability.
Innovation Solution
The spacer grid strip features interlaced strips with a cantilevered tab forming a spring and a contact portion that biases fuel rods away from the wall, combined with a motion limiter to limit rod motion and reduce flow resistance, allowing coolant flow and supporting fuel rods effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring and motion limiters protrude from the wall portion to support fuel rods, then the fuel rod support capability is improved, but the flow resistance of the spacer grid increases
Solution Approach 1:
The spring is formed as a thin, flexible tab that can elastically deform to accommodate fuel rod positioning while presenting minimal resistance to coolant flow. The flexible nature of the thin tab allows it to provide support functionality without creating significant flow obstruction compared to rigid protruding structures.
Solution Approach 2:
The motion limiter is designed to engage only when the fuel rod displacement exceeds a certain threshold, rather than continuously obstructing the flow path. This partial action approach allows normal coolant flow to pass through while providing support only when needed, reducing overall flow resistance.
2Reliability
If the spring protrudes significantly to effectively bias the fuel rod, then the fuel rod support capability is improved, but the risk of overstress or deformation of the spring increases
Solution Approach 1:
The spring tab is designed with dynamic characteristics that allow it to adapt its deformation behavior based on the applied load. The tab can undergo larger deformations for normal fuel rod positioning while the motion limiter provides a mechanical stop to prevent excessive deformation that would cause overstress or deformation of the spring material.
Solution Approach 2:
The motion limiter acts as a preventive measure that engages before the spring tab can undergo excessive deformation. By providing this mechanical constraint in advance, the system prevents situations where the spring would be subjected to stresses beyond its elastic limits, thereby protecting the spring from permanent deformation or failure.
3Reliability
If a complex spring structure with motion limiters is used to support fuel rods, then the fuel rod support capability is improved, but the manufacturing complexity increases
Solution Approach 1:
The spring and motion limiter are merged into a single integrated component formed from one continuous tab, eliminating the need for separate parts and complex assembly operations. This unified structure reduces manufacturing complexity while maintaining the dual functionality of spring support and motion limitation.
Solution Approach 2:
The tab structure serves multiple functions simultaneously: it acts as the spring element for fuel rod support, provides the motion limiter through its geometric configuration, and maintains structural integrity of the spacer grid. This multi-functionality reduces the overall number of components needed and simplifies the overall device complexity.
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 reduces flow resistance and supports fuel rods throughout their lifetime, enhancing manufacturability and preventing overstress or deformation of the spring, while maintaining efficient coolant flow and reducing fretting risks.
Implementation Method 1
a spring comprising a cantilevered tab formed in the strip and a contact portion formed at least partially in the tab and protruding from the tab for contacting the fuel rod received in the cell
Data Source
AI summary
The strip is of the type comprising a wall portion for delimiting a cell with interlaced strips, a spring formed in the strip and provided on the wall portion for biasing a fuel rod extending through the cell away from the wall portion, the spring comprising a cantilevered tab formed in the strip and a contact portion formed at least partially in the tab and protruding from the tab for contacting a fuel rod received in the cell.