Fuel Assembly Fastening Mechanism for Buoyancy-Safe Reactor Fixation
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Solution Overview
Problem
Existing nuclear reactor designs face challenges in securely fixing fuel assemblies, particularly in molten metal-cooled reactors where buoyancy issues and neutron-induced embrittlement compromise the reliability and safety of spring-loaded fixation mechanisms, leading to potential breakage and operational risks.
Innovation Solution
A fuel assembly fastening mechanism using a lattice structure with a holding lever and securing wedge that relies on static pressure for fixation, eliminating friction forces and utilizing coolant and buoyancy for secure alignment, allowing individual handling of fuel assemblies without reliance on spring-loaded components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spring-loaded elements are used to stabilize fuel assemblies vertically through friction, then fixation force is provided to counteract buoyancy, but the metal components experience neutron embrittlement causing force changes and potential breakage
Solution Approach 1:
The patent removes spring-loaded elements from the fuel assembly fixation mechanism. Instead, it uses a holding lever with a nose that engages with a nozzle window, creating a frictionless mechanical connection that eliminates neutron embrittlement risks while maintaining reliable fixation against buoyant forces
Solution Approach 2:
The patent replaces the spring-loaded friction-based mechanical system with a lever-based mechanical advantage system. The holding lever rotates about an axis and uses a nose that contacts the nozzle window perpendicularly, substituting elastic deformation (springs) with rigid body mechanics (lever rotation) to achieve fixation without neutron-sensitive materials
2Reliability
If holding lever contact surface is perpendicular to fuel assembly main axis, then static load mechanism eliminates friction forces, but insertion and removal forces must overcome static pressure
Solution Approach 1:
The patent employs a dynamic holding lever that rotates about an axis between locked and unlocked positions. During normal operation, the perpendicular contact creates static load with no friction. During insertion/removal, the lever rotates to change the contact geometry, allowing force application parallel to the main axis to overcome the static pressure and engage/disengage the locking mechanism
3Adaptability or versatility
If individual fuel assembly handling is enabled, then operational flexibility is improved, but fixation mechanism complexity increases
Solution Approach 1:
The patent assigns an independent holding lever mechanism to each fuel assembly, allowing individual operation. Each holding lever is independently rotatable and can be engaged or disengaged separately, enabling individual fuel assembly handling while keeping each unit's complexity manageable through modular design
Solution Approach 2:
Instead of having a complex centralized locking system that locks multiple assemblies together, the patent inverts the approach by giving each assembly its own simple locking lever. This distributes the complexity across multiple simple units rather than concentrating it in one complex system, achieving individual handling capability
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
Ensures reliable and safe fixation of fuel assemblies, minimizing wear and operational risks, enabling flexible and efficient handling of fuel assemblies even in buoyant conditions, thus enhancing nuclear reactor operation safety and flexibility.
Implementation Method 1
relying on static pressure for secure fixation
Implementation Method 2
the fuel assemblies can be buoyant within the coolant, e.g. in molten metal-cooled nuclear reactors like lead-cooled nuclear reactors
Data Source
Figure 1~2
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AI summary
A fuel assembly fastening mechanism (24) for use in a nuclear reactor (10) includes a fuel assembly (22) comprising a fuel assembly header (28) and a fuel assembly footer (30). The fuel assembly footer (30) has a footer housing and comprises a holding lever having a nose, the holding lever being rotatable between an unlocked position and a locked position. The fuel assembly (22) further comprises a securing wedge arranged within the fuel assembly footer (30), the securing wedge being movable between an upper position and a lower position. When the securing wedge is in one position chosen from the upper position and the lower position, the holding lever is in the unlocked position, and when the securing wedge is in the other position chosen from the upper position and the lower position, the holding lever is in the locked position. The fuel assembly fastening mechanism further includes a nozzle for mounting the fuel assembly in an open cell (20) of a bottom core plate (18) of the nuclear reactor (10), the nozzle comprising a nozzle housing engaging the footer housing and a nozzle window. The nose of the holding lever is received by the nozzle window in the locked position of the holding lever such that a contact surface between the nose of the holding lever and the nozzle window is arranged perpendicular to a fuel assembly main axis. Further, a method for operating a fuel assembly fastening mechanism (24) and a fuel assembly (22) is shown.