Boiling Water Reactor Fuel Element Throttle Design
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Solution Overview
Problem
Existing fuel elements for boiling water reactors have limited variability in pressure loss coefficients, making it difficult to achieve desired mass flow distribution and stability, especially when using primary orifices of different sizes, as adjustments to primary orifices are impractical and secondary orifices can only vary pressure loss within a narrow range.
Innovation Solution
A fuel element design featuring a throttle element with a centrally arranged impact body and edge region in the flow channel, allowing interaction with the cooling water flow regardless of primary orifice size, enabling adjustment of pressure loss coefficients over a broader range by varying the width and shape of the edge region and webs, and fine-tuning through edge design and transition area configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional secondary orifice is used in the fuel assembly base, then the pressure loss can be adjusted, but the adjustment range is very narrow and cannot accommodate different primary orifice sizes
Solution Approach 1:
The throttle element is segmented into multiple independent components: an impact body with a specific cross-sectional area, webs connecting the impact body to the base, and an edge region. This segmentation allows each component to contribute differently to the pressure loss, enabling a broader adjustment range by varying the dimensions and configuration of individual segments rather than relying on a single orifice parameter.
Solution Approach 2:
The invention transitions from a traditional single-parameter orifice design to a multi-dimensional throttle element structure. The pressure loss is now determined by multiple geometric parameters including the impact body cross-sectional area, web dimensions and spacing, and edge region characteristics. This dimensional expansion provides additional degrees of freedom for adjusting pressure loss across a wider range to match different primary orifice sizes.
2Reliability
If primary orifices are firmly connected to the lower core grid, then structural stability is maintained, but any change to primary orifices requires great technical effort and is practically impossible
Solution Approach 1:
The pressure loss adjustment function is extracted from the primary orifice system and relocated to the fuel assembly base through the throttle element. The primary orifices remain firmly connected to the lower core grid for structural stability, while the throttle element provides the necessary pressure loss tuning capability independently. This separation allows each subsystem to fulfill its primary function without compromising the other.
Solution Approach 2:
The throttle element acts as an intermediary component between the primary orifice system and the fuel rods. It mediates the flow of cooling water, adjusting the pressure loss in a manner that complements the fixed primary orifices. This intermediary structure enables pressure loss tuning without requiring modifications to the firmly connected primary orifice system.
3Reliability
If the fuel element pressure loss is optimized for dry-out and stability behavior, then reactor core stability is improved, but the pressure loss coefficient must be precisely matched between primary and secondary orifices
Solution Approach 1:
The throttle element introduces local quality variations through its differentiated structure: the impact body creates a localized pressure drop, the webs provide intermediate flow resistance, and the edge region contributes additional pressure loss. By optimizing the local geometry of each component, the overall pressure loss can be precisely tuned to achieve desired dry-out and stability characteristics without requiring complex matching between primary and secondary orifices.
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 allows for precise adjustment of pressure loss coefficients and drag coefficients, enabling uniform fuel assembly performance across different zones of the reactor core without requiring adjustments to primary orifices, thus maintaining reactor core stability and efficiency.
Implementation Method 1
the pressure loss of the fuel elements used must be adjusted to the desired mass flow distribution
Implementation Method 2
a flow channel through which cooling water flows during operation of the reactor
Data Source
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AI summary
The invention relates to a fuel element (100) for a boiling water reactor, having a multiplicity of fuel rods (102) which are combined to form a bundle and which stand with the lower end thereof on a lower holding plate (311), and having a fuel element base (101), the upper outlet opening of which faces toward the holding plate (311) and the lower inlet opening of which faces toward a lower core grate (201) of the boiling water reactor, wherein a flow duct (301) extends through the fuel element base (101) between the upper outlet opening and a lower inlet opening along a central longitudinal axis (A), which flow duct (301) is traversed by cooling water during operation, wherein the fuel element base (101) has a throttle element (302) which is spaced apart from the inlet and outlet openings in the direction of the central longitudinal axis (A) and which comprises an impact body (303) which is held centrally in the flow duct (301) by a plurality of webs (401) which extend transversely with respect to the central longitudinal axis (A), which impact body (303) occupies a part of the cross-sectional area of the flow duct (301).