Nuclear Fuel Hold-Down Assembly with Instrumentation Channel
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Solution Overview
Problem
Conventional nuclear reactor designs face challenges in securing fuel assemblies due to hydraulic forces, which can cause them to float and vibrate, and in accessing and shielding top-mounted instrumentation systems without disrupting the hold-down mechanisms.
Innovation Solution
A hold-down assembly featuring a base plate secured by a cylindrical tube spring guide with springs and a hold-down bar, which compresses against the reactor's upper core plate, providing a defined channel for top-mounted instrumentation and shielding against cross flows, while allowing for the insertion and removal of in-core instrumentation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional hold-down mechanisms are used to secure fuel assemblies, then fuel assembly stability is improved, but access to top-mounted instrumentation is hindered and shielding from cross flows is insufficient
Solution Approach 1:
The hold-down mechanism is segmented into modular components: a hold-down bar, a base plate with central opening, and spring guides. This segmentation allows the base plate to provide instrumentation access through its central opening while the hold-down bar provides securing force, resolving the contradiction between stability and accessibility.
Solution Approach 2:
The base plate serves multiple functions simultaneously: it provides a mounting surface for the hold-down mechanism, creates a central channel for instrumentation access, and works with the hold-down bar to provide cross-flow shielding. This multi-functionality resolves the contradiction by integrating stability and accessibility functions into a single component.
2Stability of the object's composition
If conventional hold-down mechanisms are used to secure fuel assemblies, then fuel assembly stability is improved, but shielding against cross flows is insufficient
Solution Approach 1:
The hold-down bar and base plate are merged into an integrated assembly where the base plate extends beneath the hold-down bar to form a continuous shielding structure. This merging creates effective cross-flow shielding while maintaining the hold-down function, resolving the contradiction between stability and harmful factor protection.
3Measurement precision
If top-mounted instrumentation systems are added, then measurement capability is improved, but the hold-down mechanism complexity increases
Solution Approach 1:
The base plate is designed with a central opening that serves dual purposes: it allows instrumentation to pass through for measurement capabilities while simultaneously serving as part of the hold-down mechanism structure. This multi-functionality adds measurement capability without increasing hold-down mechanism complexity.
4Ease of operation
If instrumentation channels are created in the hold-down assembly, then instrumentation access is improved, but structural integrity may be compromised
Solution Approach 1:
The base plate is designed with a central opening for instrumentation access, but the material distribution and thickness are optimized locally to maintain sufficient structural integrity. The opening is positioned and sized to provide instrumentation access while minimizing impact on the overall strength of the hold-down assembly.
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
Effectively secures fuel assemblies and protects instrumentation from cross flows, maintaining reactor stability and performance with minimal modifications to existing hold-down devices.
Implementation Method 1
a spring or coil springs (98) circumscribing an outer surface of the spring guide (94)
Implementation Method 2
hydraulic forces, which can cause them to float and vibrate
Implementation Method 3
The hold-down bar (96) rests against the upper core plate (40) when the fuel assembly is installed in the reactor core
Implementation Method 4
a portion of that extension protrudes above the upper core plate (40) to fully shield the instrumentation shroud from exposure to the upper core outlet flow jet disturbances as well as the induced cross flow
Data Source
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AI summary
A plate mounted fuel assembly hold-down system (88) that provides a defined channel for both the insertion and removal of reactor head mounted, fixed in-core detector instrumentation, provides a guided path for the fixed in-core detector during insertion, and shields the instrument shroud against coolant cross flow. The hold-down assembly (88) includes a base plate (90) that seats on the adapter plate (84) of the fuel assembly (22) and has openings that align with the control rod guide thimbles. A hollow sleeve extends through and below a central opening (92) in the base plate to mate with the fuel assembly instrument thimble (110). The sleeve extends above the base plate and through and above an upper core plate (40) of the reactor. A hold-down bar (96) is slidably mounted on the sleeve and is restrained below the top of the sleeve. A spring (98) is positioned around the sleeve and is captured between the hold-down bar and the base plate.