Fuel Assembly Reinforcement Segments for Damaged Spacer Stability
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Solution Overview
Problem
In nuclear reactors, particularly boiling water reactors, fuel rods experience oxidation and irradiation-induced growth, leading to uneven material expansion that can cause spacers to become damaged or displaced, resulting in fuel elements becoming jammed and compromising accident-proof storage and transport safety, necessitating labor-intensive re-skeletonization with increased radiation exposure.
Innovation Solution
The method involves inserting first and second strengthening structure segments with support structures between fuel rods, using nickel-chromium-iron-molybdenum alloy or zirconium alloy, to reinforce the fuel assembly without removing existing spacers, ensuring safe storage and transport by maintaining fuel rod spacing and preventing relative movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing spacers are mechanically removed and replaced with new ones (re-skeletonization process), then the fuel assembly can be restored to functional condition, but the process requires considerable human labor and increases radiation dose exposure to workers
Solution Approach 1:
The upgrading structure is divided into multiple segments that can be inserted independently between fuel rods. Each segment contains support structures that can be positioned at specific locations, allowing partial reinforcement rather than complete disassembly and replacement of the spacer system.
Solution Approach 2:
The upgrading structure segments are designed to be inserted into the existing fuel assembly structure without removing the original spacers. The support structures nest between the fuel rods, integrating with the existing assembly while providing additional reinforcement.
2Ease of operation
If the fuel assembly channel and spacers are left without reinforcement, then the assembly can be easily handled, but oxidation and irradiation cause growth that leads to fuel elements becoming jammed and spacers being damaged during removal
Solution Approach 1:
The upgrading structure is installed in advance during the upgrading process, providing reinforcement before the fuel assembly is placed back into service. This preliminary reinforcement prevents future jamming and damage that would occur during normal operation and removal cycles.
Solution Approach 2:
The upgrading structure acts as a protective cushion or buffer between the fuel rods and the fuel assembly channel walls. This beforehand protection absorbs the effects of oxidation and irradiation-induced growth, preventing direct contact and damage between the spacers and channel structures.
3Reliability
If labor-intensive re-skeletonization is performed to replace damaged spacers, then complete spacer functionality is restored, but the process increases radiation exposure and requires significant human intervention
Solution Approach 1:
Instead of completely replacing all spacers through full re-skeletonization, the invention applies partial action by inserting upgrading structure segments only at specific locations where reinforcement is needed. This provides sufficient reliability improvement without requiring complete disassembly and replacement of the entire spacer system.
Data Source
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AI summary
Within the scope of the method presented here, strengthening structure segments (1, 7) are introduced into the fuel assembly (14) at one or more positions (25, 26) in order to achieve an as-designed mounting of the fuel rods (15) of the fuel assembly (14) that achieves fixing of the fuel rods (15) transversely to a longitudinal direction (16) in which the fuel rods (15) extend in such a way as to prevent a relative movement of fuel rods (15) with respect to one another, even in the case of a malfunction. It is not absolutely necessary here to remove defective or displaced spacers which are present. Thus, fuel assemblies (14) can be strengthened in a simple manner for transport and/or storage.