Lock-Support Spacer Grid for Nuclear Fuel Rod Restraint
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Solution Overview
Problem
Conventional nuclear fuel assemblies face issues with fuel rod cladding restraint, leading to fretting and potential breach due to hydraulic forces and turbulence, as well as surface damage during assembly, which can result in corrosion and cladding failure.
Innovation Solution
An improved spacer grid design featuring an egg-crate base grid with lock-support sleeves that rotate to apply transverse pressure on fuel rods, preventing axial and radial movement while allowing thermal growth, and a method for loading fuel rods without damaging the cladding, using a tool to rotate the sleeves into position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional spring grids are used to restrain fuel rods, then fuel rod movement is restrained, but cladding surface damage and fretting occur
Solution Approach 1:
The patent employs a flexible lock-support sleeve that can rotate and deform elastically to engage with the fuel rod. The sleeve's flexibility allows it to apply restraining forces without creating rigid contact points that cause surface damage. The thin-walled construction enables the sleeve to conform to the fuel rod surface while maintaining restraint capability, thereby preventing fretting and surface damage while ensuring cladding integrity.
2Manufacturing precision
If fuel rods are tightly restrained during assembly, then positioning accuracy is improved, but cladding surface damage occurs
Solution Approach 1:
The lock-support sleeve is designed to be rotatable and dynamically adjustable during the fuel rod loading process. Initially, the sleeve can rotate freely to allow easy insertion of the fuel rod with high positioning accuracy. Once positioned, the sleeve can be locked in place to provide stable restraint without applying excessive static pressure that would damage the cladding surface. This dynamic capability enables precise positioning while preventing surface damage.
3Reliability
If complex restraint mechanisms are used to prevent fuel rod movement, then fuel rod stability is improved, but device complexity increases
Solution Approach 1:
The lock-support sleeve serves multiple functions within a single component: it provides radial restraint to prevent fuel rod movement, allows for rotational adjustment during loading, and can be locked in position to maintain stability. By combining these functions into one universal element, the patent achieves fuel rod stability without requiring multiple separate complex mechanisms, thereby reducing overall device complexity while maintaining reliability.
Data Source
AI summary
An improved grid for a nuclear reactor fuel assembly that has an egg-crate base grid as the primary support structure with each support cell of the base grid that supports a fuel rod having a lock-support sleeve that is rotatable within the support cell between a first and second orientation. In the first orientation the lock-support sleeve fits loosely within the support cell of the base grid and respectively, loosely receives the fuel rods that are loaded therein. The lock-support sleeves are then rotated to a second orientation that locks the fuel rods axially within the support cells.