Nuclear Reactor Fuel Element Expanders for Radial Spacing
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Solution Overview
Problem
Fast reactors cooled by liquid metals face challenges in maintaining core geometry stability and reactivity control due to temperature-induced expansions and deformations, which can lead to uncontrolled reactivity increases and assembly errors during refueling.
Innovation Solution
The nuclear reactor incorporates a support system with radially expandable fuel elements and elastic constraints, featuring alternating low and high thermal expansion materials in the expanders, allowing for differential thermal expansion and maintaining core compactness while permitting rotation during refueling, thus preventing uncontrolled reactivity and assembly errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fuel elements are assembled with minimum distance to maintain core compactness, then reactivity control is improved, but refueling becomes problematic due to fuel deformations and swelling
Solution Approach 1:
The fuel element is divided into two distinct parts: an active part containing the fuel and a service part containing the expander mechanism. This segmentation allows the active part to remain compact for reactivity control while the service part provides the mechanical function of expansion to facilitate refueling operations.
Solution Approach 2:
The expander mechanism changes its physical state based on temperature parameters. During normal operation, the expander remains contracted to maintain core compactness. During refueling operations, the expander expands to create the necessary clearance, dynamically adjusting the geometry to resolve the contradiction between compactness and accessibility.
2Reliability
If bimetallic elements are used to amplify arching in a predetermined direction, then thermal expansion effects are enhanced, but assembly errors produce opposite results and rotations are not permitted
Solution Approach 1:
The expander mechanism employs an asymmetric design with cam profiles that are specifically shaped to control the expansion motion. The cam and cam follower arrangement creates a predetermined expansion path that is insensitive to assembly orientation, allowing the mechanism to function correctly regardless of how the fuel element is positioned during assembly.
Solution Approach 2:
Instead of using bimetallic elements that arch in a predetermined direction (which requires precise assembly orientation), the invention inverts the approach by using a mechanically actuated expander that creates clearance through controlled expansion. This inversion makes the system insensitive to assembly orientation while still achieving the desired thermal expansion effects.
3Reliability
If fuel elements are kept compact to prevent uncontrolled reactivity increase, then safety is improved, but space for thermal expansion is restricted
Solution Approach 1:
The system dynamically adjusts the spacing between fuel elements based on operational requirements. During normal power operation, the expanders remain contracted to maintain core compactness and safety. During refueling operations, the expanders extend to provide the necessary clearance, allowing the system to adapt its geometry to different operational states.
Solution Approach 2:
The expander mechanisms are pre-positioned within the fuel element structure during manufacturing. This preliminary configuration allows the expanders to quickly deploy when needed for refueling operations without requiring complex assembly procedures, and ensures they are ready to maintain compactness during normal operation.
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 enhances safety by controlling reactivity through controlled radial expansion, allowing for efficient refueling and minimizing reactivity fluctuations, while ensuring the core remains compact and stable during normal and accident conditions.
Implementation Method 1
expanders (50) which, in cold assembly conditions, maintain their projection within the horizontal projection of the outline of the fuel elements (12) and radially expand when the core output temperature exceeds a predetermined reference value
Implementation Method 2
featuring alternating low and high thermal expansion materials in the expanders, allowing for differential thermal expansion
Implementation Method 3
a system of constraints and rigidities of relative component parts, such as to make said spacing mechanically possible
Data Source
AI summary
The present invention concerns a nuclear reactor, preferably a pool-type nuclear reactor cooled by liquid metal or molten salts, having a core formed of a bundle of fuel elements and immersed in a primary fluid for cooling the core; the fuel elements are provided with expanders acting in a direction perpendicular to the axes of the fuel elements and having low thermal expansion elements which engage alternatively with high thermal expansion elements to amplify the radial expansion of respective end elements which, when a predetermined temperature is exceeded, engage with each other and space the fuel elements from one another and in particular their active part to introduce negative reactivity into the core.