Nuclear Fuel Assembly Lifting Tool for Constrained Core Access
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Solution Overview
Problem
Current refueling methods for nuclear reactors are hindered by the need for a large working space due to the swinging motion of grappling hooks, which is constrained by adjacent fuel assemblies, and the challenge of removing control rod assemblies during refueling without disrupting neutron suppression.
Innovation Solution
A lifting tool with downwardly extending elements that surround and overlap the control rod assembly, allowing for secure attachment and removal of fuel assemblies without requiring a large working space, enabling the lifting tool to accommodate control rods extending above the fuel assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional grappling hooks with swinging motion are used for fuel assembly removal, then the fuel assembly can be engaged and lifted, but a large working space is required which is constrained by adjacent fuel assemblies
Solution Approach 1:
The lifting tool is divided into multiple downwardly extending elements (typically three or more) that can be independently positioned and locked onto the fuel assembly. This segmentation allows the tool to engage the fuel assembly from multiple points simultaneously, eliminating the need for a single-point engagement that requires swinging motion and large working space.
Solution Approach 2:
The invention transitions from a horizontal/swinging engagement mechanism to a vertical engagement mechanism. The downwardly extending elements engage the fuel assembly from above in a vertical direction, utilizing the vertical dimension rather than horizontal swinging motion, thereby reducing the required working space within the constrained reactor core environment.
2Productivity
If control rod assemblies are removed during refueling, then fuel assembly replacement can proceed, but neutron suppression is disrupted
Solution Approach 1:
The lifting tool is designed to accommodate both the fuel assembly and the control rod assembly simultaneously. The downwardly extending elements are positioned to engage the fuel assembly while the open central region allows the control rod assembly to remain in place, merging the lifting function with the neutron suppression function into a single integrated operation.
Solution Approach 2:
The lifting tool serves multiple functions: it lifts the fuel assembly for removal or installation, accommodates the control rod assembly during the process, and maintains neutron suppression capability. This multi-functionality eliminates the need to separately remove control rods, thereby maintaining both productivity and reliability.
3Area of stationary object
If lifting tool with downwardly extending elements is used, then working space requirement is reduced, but the tool structure becomes more complex
Solution Approach 1:
The downwardly extending elements are nested within a common support structure that connects to the crane. The elements can be positioned and locked independently while remaining part of an integrated tool assembly, reducing the overall structural complexity compared to having completely separate components for each engagement point.
Solution Approach 2:
The downwardly extending elements incorporate self-locking mechanisms that automatically engage with the fuel assembly during the lowering process. This self-service capability reduces the need for complex external locking mechanisms and simplifies the overall tool structure while maintaining secure engagement.
Data Source
AI summary
Refueling of a nuclear reactor (40) includes removing a fuel assembly (10). The removal method includes lowering a lifting tool (80) of a crane (44) onto a top of the fuel assembly. The lowered lifting tool including a plurality of downwardly extending elements (82) that surround and vertically overlap a portion (74) of a control rod assembly (70) extending above the top of the fuel assembly. The downwardly extending elements are locked with corresponding mating features (26) at the top of the fuel assembly to connect the lifting tool with the fuel assembly. The connected fuel assembly is moved into a spent fuel pool (42) using the crane, and the lifting tool is disconnected from the top of the fuel assembly by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.