Multi-Pitch Wire-Wrapped Fuel Assembly for Coolant Flow Balancing
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Solution Overview
Problem
Nuclear fuel assemblies experience a temperature gradient across fuel pins due to uneven coolant flow, leading to thermodynamic stresses and strains, which can be mitigated by varying the wire wrapping pitch and clocking angle of fuel pins to improve thermal-hydraulic performance.
Innovation Solution
Implementing a multi-pitch wire wrap design for fuel pins, where pins closer to the fuel assembly duct have a shorter pitch than those in inner rings, and adjusting clocking angles to avoid wire-to-wire interference, thereby enhancing coolant mixing and pressure drop distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform wire wrapping pitch is used for all fuel pins, then the manufacturing process is simple, but a temperature gradient develops across the fuel pins due to uneven coolant flow distribution
Solution Approach 1:
The patent applies different wire wrapping pitches to different radial positions of fuel pins. Specifically, fuel pins in the inner region (first set) use a first pitch while fuel pins in the outer region (second set) use a second pitch that is a multiple of the first pitch. This local differentiation optimizes coolant flow distribution and reduces temperature gradients across the fuel assembly.
2Ease of manufacture
If fuel pins near the duct wall have the same wire wrapping pitch as inner fuel pins, then the wire wrapping process is simplified, but coolant flows too quickly through edge subchannels reducing heat removal efficiency
Solution Approach 1:
The patent implements location-specific wire wrapping pitches where outer fuel pins (closer to duct wall) use a different pitch than inner fuel pins. This creates localized flow resistance in edge subchannels, slowing coolant flow and improving heat removal efficiency from fuel pins near the duct wall.
3Device complexity
If a single wire wrapping pitch is used throughout the fuel assembly, then the design is simple, but the outlet temperature of the nuclear reactor is limited
Solution Approach 1:
The patent changes the wire wrapping pitch parameter radially across the fuel assembly. By using a first pitch for inner fuel pins and a second pitch (a multiple of the first) for outer fuel pins, the design optimizes coolant flow distribution to increase the outlet temperature of the nuclear reactor while maintaining manageable design complexity.
4Ease of manufacture
If fuel pins are positioned in different rings with the same wire wrapping characteristics, then manufacturing is consistent, but thermodynamic stresses and strains increase due to temperature gradients
Solution Approach 1:
The patent applies differentiated wire wrapping pitches to fuel pins in different radial rings. Inner rings use a first pitch while outer rings use a second pitch, creating a gradient that reduces temperature differences between center and edge fuel pins, thereby reducing thermodynamic stresses and strains while maintaining manufacturing consistency through systematic variation.
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 reduces the temperature gradient across fuel pins, increases outlet temperature, and improves thermal-hydraulic performance without exceeding thermomechanical limits, resulting in a more efficient nuclear reactor operation.
Implementation Method 1
a nuclear fuel pin is wrapped by a circular wire in a helical pattern
Implementation Method 2
As coolant flows in the subchannels, there is typically a greater pressure drop in interior subchannels as compared to edge subchannels
Data Source
AI summary
A nuclear fuel assembly is constructed with fuel assembly components that are wire wrapped and positioned in hexagonal rings within a fuel assembly duct. The fuel assembly components positioned in an outermost ring of the fuel assembly are wire wrapped with a pitch that is shorter than fuel assembly components positioned at an interior ring of the fuel assembly. The shorter pitch at the outer ring of the fuel assembly increases pressure drop of a coolant fluid at the edge and corner subchannels and thereby reduces the temperature gradient across the fuel assembly, which provides a higher output temperature of the nuclear reactor without substantially increasing peak temperature of the fuel cladding.