Nuclear Reactor Core Shroud Alignment Configuration
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Solution Overview
Problem
In nuclear reactor designs, maintaining the alignment of upper and lower internals during thermal expansion and contraction is challenging, especially in advanced passive plant designs where protruding alignment pins are not feasible, making it difficult to manufacture, install, and remove the core shroud assembly without compromising rotational stability.
Innovation Solution
The design incorporates jacking block assemblies with radially extending jacking studs and vertically spaced alignment posts around the core shroud top plate, allowing for alignment and load transfer without hardware removal, facilitating easy installation and potential removal of the core shroud assembly, and accommodating differential thermal expansion with a hard surface liner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alignment pins are used to maintain lateral alignment of upper core plate, then alignment is achieved, but the design becomes incompatible with advanced passive plant core shroud assemblies and complicates removal operations
Solution Approach 1:
The alignment system is segmented into multiple functional components: alignment pins for lateral positioning, notches for angular orientation, and clearance features for thermal expansion. This segmentation allows each component to perform its specific function independently, achieving precise alignment without requiring a complex integrated system.
Solution Approach 2:
Instead of using protruding pins that extend outward from the core shroud, the invention inverts the approach by using pins that are received within recesses and notches in the core shroud assembly. This inversion allows alignment to be achieved while maintaining a compact profile that is compatible with passive plant designs and facilitates easier removal operations.
2Stability of the object's composition
If alignment pins are made rigid to maintain precise alignment, then alignment stability is improved, but thermal expansion and contraction during power ramp-up and cool down cannot be accommodated
Solution Approach 1:
The alignment system incorporates dynamic features that allow it to adapt to thermal changes. The clearance between alignment pins and their receiving features, along with the notched geometry, enables the upper core plate and core shroud to move relative to each other during thermal expansion and contraction while maintaining proper alignment. This dynamic capability allows the rigid pins to provide stability while the system as a whole accommodates thermal variations.
Solution Approach 2:
The invention changes the geometric parameters of the alignment features, specifically designing notches with specific angular orientations (e.g., 45 degrees) and clearances that allow for thermal movement. These parameter changes enable the alignment system to maintain precision while accommodating the physical changes that occur during reactor operation cycles.
3Manufacturing precision
If protruding alignment pins are used to align core shroud, then alignment is achieved, but hardware removal becomes necessary during maintenance outages
Solution Approach 1:
The invention inverts the conventional protruding pin design by using pins that are received within recesses and notches in the core shroud assembly. This inverted configuration eliminates the need for hardware removal during maintenance, as the pins are already positioned within the structure and can be easily accessed and removed if necessary, significantly improving maintenance accessibility.
4Ease of repair
If alignment features are simplified for easy removal, then maintenance accessibility is improved, but rotational stability during operation may be compromised
Solution Approach 1:
The alignment system is segmented into multiple functional components: alignment pins for lateral positioning, notches for angular orientation, and clearance features for thermal expansion. This segmentation allows each component to perform its specific function independently, achieving precise alignment without requiring a complex integrated system.
Solution Approach 2:
The notches are designed with specific asymmetric angular orientations (e.g., 45 degrees) that provide rotational stability by preventing unwanted rotation of the upper core plate relative to the core shroud. The asymmetric geometry ensures that the alignment features engage in a way that maintains rotational stability during operation while still allowing for easy removal when needed.
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 solution ensures precise alignment and stability of the core shroud and upper core plate during assembly and operation, simplifies the manufacturing and installation process, and allows for easy removal of the core shroud assembly, reducing the complexity and time required for field operations.
Implementation Method 1
The pins must laterally support the upper core plate so that the plate is free to expand radially and move axially during differential thermal expansions between the upper internals and the core barrel
Data Source
AI summary
An alignment system that employs jacking block assemblies and alignment posts around the periphery of the top plate of a nuclear reactor lower internals core shroud to align an upper core plate with the lower internals and the core shroud with the core barrel. The distal ends of the alignment posts are chamfered and are closely received within notches machined in the upper core plate at spaced locations around the outer circumference of the upper core plate. The jacking block assemblies are used to center the core shroud in the core barrel and the alignment posts assure the proper orientation of the upper core plate. The alignment posts may alternately be formed in the upper core plate and the notches may be formed in top plate.