Nuclear Fuel Bundle Guard Rings for Thermal Striping
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Solution Overview
Problem
Liquid metal cooled nuclear reactors, such as sodium cooled fast reactors, experience thermal striping due to hot and cold spots in the sodium flow exiting the fuel bundles, leading to damaging thermal stresses in the primary vessel over time.
Innovation Solution
The fuel bundle design includes a channel with a nose assembly and multiple fuel rods, where at least one fuel rod is surrounded by a guard ring for spacing, and some fuel rods are helically wrapped with wire, while others are not, to reduce bulk sodium rotation and promote sodium flow mixing, thereby minimizing thermal striping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If fuel bundles are used in liquid metal cooled reactors, then nuclear energy generation is achieved, but thermal striping occurs causing thermal stresses in the primary vessel
Solution Approach 1:
The fuel bundle is segmented into multiple fuel rods with guard rings at specific positions. These guard rings divide the sodium flow path into multiple channels, preventing large-scale thermal striping by distributing the thermal loads across different flow paths. The segmentation of the flow path directly addresses the thermal stress problem while maintaining energy generation capability.
Solution Approach 2:
Guard rings are introduced as intermediary structures between adjacent fuel rods. These guard rings act as mediators that redirect sodium flow and prevent direct thermal coupling between hot and cold spots. The guard rings serve as intermediate flow path elements that mitigate thermal striping effects while allowing the reactor to continue generating power.
2Object-affected harmful factors
If guard rings are added to fuel rods, then thermal striping is reduced, but device complexity increases
Solution Approach 1:
Rather than modifying the entire fuel bundle uniformly, guard rings are strategically placed at specific locations where thermal striping is most problematic. The guard rings are positioned at specific axial locations and only on certain fuel rods, applying the solution locally where needed rather than throughout the entire system, thus reducing overall complexity while maintaining effectiveness.
Solution Approach 2:
The patent applies guard rings to only some fuel rods rather than all fuel rods, or at selected positions along the fuel rod length. This partial application of the guard ring concept provides sufficient thermal striping mitigation without the full complexity of implementing guard rings on every fuel rod throughout their entire length, balancing effectiveness with structural simplicity.
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 thermal stresses on the fuel bundle components, extending the equipment's lifetime by minimizing thermal striping and promoting uniform sodium flow within the reactor core.
Implementation Method 1
the wire wrappings generate a Magnus force that induces a rotation of a sodium flow passing through the fuel bundle
Implementation Method 2
the rotating sodium flow creates a centrifugal force that promotes mixing of the sodium flow and minimizes thermal striping
Data Source
AI summary
In one embodiment, the fuel bundle for a liquid metal cooled reactor includes a channel, a nose assembly secured to a lower end of the channel, and a plurality of fuel rods disposed within the channel. At least one of the fuel rods has at least one guard ring surround the fuel rod and spacing the fuel rod from adjacent fuel rods.