Bimetallic Spring Fuel Assembly Gap Control
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Solution Overview
Problem
Nuclear fuel assemblies experience misalignment and increased impact loads during reactor operation due to gaps between fuel assemblies, which can lead to power penalties and increased risk during seismic/LOCA events, necessitating a solution to reduce or eliminate these gaps while maintaining clearance for fuel handling during outages.
Innovation Solution
Incorporation of bimetallic springs that expand and contact adjacent components at operating temperatures, reducing fuel assembly gaps and providing alignment benefits, and designed to absorb seismic/LOCA loads, with configurations such as rectangular or circular disc shapes attached to grid straps or nozzles, using materials like INVAR™ and stainless steel for optimal deflection and load capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gaps are maintained between fuel assemblies, then fuel handling during outages is facilitated, but misalignment and impact loads increase during reactor operation
Solution Approach 1:
The patent employs a dynamic support feature that transitions between two states: during reactor operation, the spring is compressed to push fuel assemblies together, eliminating gaps and preventing misalignment; during outages, the spring relaxes to allow gaps that facilitate fuel handling. This dynamic behavior resolves the contradiction by adapting the spacing to operational requirements.
Solution Approach 2:
The support feature utilizes thermal expansion parameters to automatically adjust the spacing between fuel assemblies. As the reactor core temperature changes during operation versus outage conditions, the material properties of the support feature change, causing it to expand or contract accordingly. This parameter change enables the system to maintain optimal spacing for either operational integrity or maintenance access.
2Reliability
If fuel assemblies are closely spaced, then alignment and impact load resistance improve, but clearance for fuel handling during outages is reduced
Solution Approach 1:
The spring-loaded support feature dynamically adjusts the clearance between fuel assemblies based on operational state. During operation, the spring is compressed to minimize gaps and maximize alignment; during outages, the spring expands to provide necessary clearance for handling operations. This dynamic mechanism resolves the contradiction by making the spacing adaptable rather than fixed.
Solution Approach 2:
The support feature is pre-configured with a spring mechanism that automatically performs the action of creating clearance or applying pressure as needed. The spring is pre-loaded to provide the necessary force, eliminating the need for manual adjustment or complex control systems during operational transitions.
3Productivity
If gaps between fuel assemblies are reduced, then power penalties are minimized, but structural support complexity increases
Solution Approach 1:
The support feature is designed to be self-regulating, using the thermal expansion properties of its material to automatically adjust and maintain optimal spacing between fuel assemblies without external control systems. The spring mechanism self-adjusts based on temperature changes, eliminating the need for complex active control systems while maintaining high power efficiency.
Solution Approach 2:
The patent utilizes material parameter changes, specifically thermal expansion coefficients, to achieve automatic spacing adjustment. By selecting materials with appropriate thermal expansion properties, the support feature naturally compensates for thermal effects during reactor operation, maintaining optimal fuel assembly spacing to minimize power penalties without requiring complex active control 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
The bimetallic spring feature effectively reduces fuel assembly gaps during operation, enhances alignment, and absorbs seismic/LOCA loads, minimizing power penalties and grid damage, while allowing for proper fuel handling and alignment during maintenance.
Implementation Method 1
a bimetallic spring that moves between a first and second position relative to the plane as the fuel assembly transitions in a reactor core from a shutdown temperature to an operating temperature
Implementation Method 2
at least some of the interconnected components have a bimetallic spring that moves between a first and second position relative to the plane
Data Source
AI summary
A nuclear fuel assembly having lateral support provided by a bimetallic spring that extends from a side of the fuel assembly under certain core conditions to pressure against an adjacent component and withdraws under other core conditions, such as shutdown, to enable the nuclear fuel assembly to be aligned or withdrawn from the core and repositioned.