SMR Control Rod Guide Assembly Suspension Design
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Solution Overview
Problem
Conventional pressurized water reactors (PWRs) face challenges in maintaining reliable control rod assembly movement and fuel assembly stability due to the weight-bearing upper core plate, which limits flow resistance reduction and introduces alignment and thermal expansion issues, especially in smaller modular reactors (SMRs) with reduced power output.
Innovation Solution
The SMR design omits the upper core plate, suspending control rod assembly guide structures from above using a support element, allowing for increased flow passages and reducing material costs, while ensuring alignment through mating features and accommodating thermal expansion with a gap between the guide structure and fuel assembly, and incorporates a heavy terminating element for enhanced weight and reduced SCRAM time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an upper core plate is used to support control rod assembly guide structures, then structural support and alignment are provided, but flow resistance is increased and manufacturing cost is increased
Solution Approach 1:
The patent removes the upper core plate from the reactor core structure, extracting this component that was causing flow resistance issues. The control rod assembly guide structures are instead supported by the pressure vessel wall and internal core structures, eliminating the need for the upper core plate while maintaining necessary structural support functions.
2Strength
If an upper core plate is used to support control rod assembly guide structures, then structural support is provided, but manufacturing cost is increased
Solution Approach 1:
The upper core plate is removed from the design, reducing the number of components that need to be manufactured and assembled. This extraction of the upper core plate directly reduces manufacturing cost while the support function is redistributed to existing structural elements.
3Manufacturing precision
If control rod assembly guide structures are rigidly fixed, then alignment is maintained, but thermal expansion is constrained causing stress
Solution Approach 1:
The patent employs expandable support structures that can dynamically adjust to thermal expansion. The guide structures include features that allow controlled movement and expansion as temperature changes, preventing stress buildup while maintaining operational alignment through mating features and gaps.
4Stability of the object's composition
If hold-down springs are used to prevent fuel assembly lift-off, then fuel assembly stability is maintained, but device complexity and manufacturing cost are increased
Solution Approach 1:
The hold-down springs are removed from the fuel assembly structure. Instead, the guide structures themselves provide stability and positioning functions through their geometric design and mating features, eliminating the need for separate hold-down spring components and reducing overall device complexity.
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 configuration enhances flow efficiency, reduces manufacturing costs, and maintains reliable control rod movement and fuel assembly stability in SMRs by eliminating the need for hold-down springs and upper core plates, while accommodating thermal expansion and providing improved alignment and support.
Implementation Method 1
accommodating thermal expansion with a gap between the guide structure and fuel assembly
Data Source
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AI summary
A pressurized water reactor (PWR) comprises a pressure vessel containing primary coolant water. A nuclear reactor core is disposed in the pressure vessel and includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of fuel rods containing a fissile material. A control system includes a plurality of control rod assemblies (CRA's). Each CRA is guided by a corresponding CRA guide structure. A support element is disposed above the CRA guide structures and supports the CRA guide structures. The pressure vessel may be cylindrical, and the support element may comprise a support plate having a circular periphery supported by the cylindrical pressure vessel. The CRA guide structures suitably hang downward from the support plate. The lower end of each CRA guide structure may include alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly.