Mixed Spacer Design for Nuclear Fuel Bundle Heat Transfer
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Solution Overview
Problem
Conventional fuel bundles in nuclear reactors face challenges in maintaining optimal operating conditions and heat transfer during both normal and transient scenarios, particularly due to the limitations of single-type spacers which can lead to dry-out patches and overheating, exacerbated by the geometry of grid-type spacers and inadequate coolant film retention by ferrule-type spacers.
Innovation Solution
Implementing a mixed-type spacer design within the same fuel bundle, where grid-type spacers with mixing vanes are used near the inlet for enhanced coolant mixing and ferrule-type spacers are used near the exit to minimize liquid film stripping, optimizing spacer types based on axial position and coolant characteristics to achieve improved heat transfer and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If grid-type spacers with mixing vanes are used throughout the fuel bundle, then coolant mixing is enhanced, but liquid film stripping increases leading to dry-out patches and overheating
Solution Approach 1:
The patent applies local quality by using different spacer types in different axial locations within the fuel bundle. Grid-type spacers with mixing vanes are placed in the lower portion (first axial location) to enhance coolant mixing where needed, while ferrule-type spacers are placed in the upper portion (second axial location) to minimize liquid film stripping. This spatial differentiation of spacer characteristics resolves the contradiction by optimizing each location's specific requirements rather than using a uniform spacer design throughout the bundle.
2Object-affected harmful factors
If ferrule-type spacers are used throughout the fuel bundle, then liquid film retention is improved, but coolant mixing is insufficient leading to reduced heat transfer efficiency
Solution Approach 1:
The patent resolves this contradiction by applying ferrule-type spacers in the upper axial location where liquid film retention is critical, while placing grid-type spacers with mixing vanes in the lower axial location where enhanced coolant mixing is needed. This localized application ensures that each spacer type performs its optimal function in the appropriate location, achieving both liquid film retention and effective coolant mixing throughout the fuel bundle.
3Device complexity
If single-type spacers are used in the fuel bundle, then device complexity is reduced, but operating conditions cannot be optimized for both normal and transient scenarios
Solution Approach 1:
The patent applies local quality by differentiating spacer types based on axial location to optimize performance under different operating conditions. The lower portion uses grid-type spacers that provide enhanced mixing during normal operation, while the upper portion uses ferrule-type spacers that maintain liquid film during transient conditions. This spatial variation in spacer characteristics allows the fuel bundle to be optimized for both normal and transient scenarios simultaneously, resolving the contradiction between device complexity and operational reliability.
4Manufacturing precision
If grid-type spacers are used near the inlet, then coolant mixing is enhanced, but heat transfer to coolant is reduced due to film stripping
Solution Approach 1:
The patent resolves this contradiction by placing grid-type spacers with mixing vanes specifically in the lower axial location (first axial location) where enhanced mixing is beneficial, while placing ferrule-type spacers in the upper axial location (second axial location) where heat transfer to coolant is critical. This localized differentiation ensures that mixing enhancement occurs where it is most effective without compromising heat transfer performance in regions where liquid film retention is essential.
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 mixed-type spacer approach enhances heat transfer during normal operations and improves resilience during transient conditions, reducing the risk of dry-out patches and fuel rod overheating, as demonstrated by full-scale bundle tests showing improved margins and reduced sensitivity to sudden coolant flow losses.
Implementation Method 1
grid-type spacers with mixing vanes are used near the inlet for enhanced coolant mixing
Implementation Method 2
ferrule-type spacers are used near the exit to minimize liquid film stripping
Data Source
AI summary
Example embodiment fuel bundles use multiple types of spacers within the same fuel bundle. The type for each spacer location may be determined based on the axial position of the spacer, the characteristics of the spacer type, and the location and coolant characteristics for the particular example fuel bundle including the spacers. Historic performance data for the particular bundle location, predictive modeling, etc. may be used to determine what spacer types at which locations result in the best operating conditions and margins for example fuel bundles.