Control Rod Blade Distance Means for Shadow Corrosion Mitigation
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Solution Overview
Problem
Shadow corrosion between zirconium-based channel boxes and stainless steel control rods in nuclear boiling water reactors leads to channel box bowing, potentially causing control rod insertion issues and interference, which can disrupt reactor operation.
Innovation Solution
The control rod design incorporates distance means, such as protrusions or ridges on its blades, to maintain a minimum distance of 0.5-2 mm from the channel box, reducing shadow corrosion and ensuring smooth insertion and operation by distributing these features along the control rod blades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If control rod blades are placed close to channel boxes, then control rod insertion efficiency is improved, but shadow corrosion increases leading to channel box bowing
Solution Approach 1:
The patent introduces an intermediary component (insulating coating or spacer) between the control rod blade and the channel box. This intermediary prevents direct metal-to-metal contact, thereby eliminating the galvanic couple that causes shadow corrosion, while still allowing the control rod to function effectively within the reactor core.
Solution Approach 2:
The patent applies a sacrificial insulating coating on the control rod blade surface. This coating is designed to be consumed or degraded over time, providing continuous protection against shadow corrosion. When the coating deteriorates, the control rod can be replaced, ensuring long-term protection without compromising the expensive channel box.
2Volume of moving object
If control rod blades are placed close to channel boxes, then reactor core space utilization is improved, but channel box bowing occurs due to shadow corrosion
Solution Approach 1:
By introducing an insulating intermediary between the control rod and channel box, the patent prevents the shadow corrosion process that would otherwise cause hydrogen absorption and subsequent bowing of the channel box, thereby maintaining its straight shape and structural integrity.
Solution Approach 2:
The patent changes the surface properties of the control rod blade by applying an insulating coating, which alters the electrochemical parameters at the interface between metal components. This parameter change prevents the galvanic corrosion process, thereby preventing the shape distortion (bowing) of the channel box.
3Quantity of substance
If control rod blades are placed close to channel boxes, then fuel assembly density is improved, but control rod interference occurs due to channel box bowing
Solution Approach 1:
The insulating intermediary prevents shadow corrosion, thereby preventing channel box bowing that would cause interference between the control rod and channel box, ensuring smooth operation and ease of control rod insertion and withdrawal.
Solution Approach 2:
The patent applies protective insulating measures beforehand to prevent shadow corrosion and subsequent channel box deformation. This preemptive protection avoids future interference problems, ensuring that control rods can operate freely without friction or binding caused by bowed channel boxes.
Data Source
AI summary
A control rod for a nuclear boiling water reactor is described. The control rod has a longitudinal centre axis and control rod blades, each control rod blade having a first and a second side and being substantially parallel to the longitudinal center axis. Each control rod blade comprises an absorber material which extends from a first absorber end to a second absorber end, the distance between the first absorber end and the second absorber end defining an active length. The control rod blades are provided with distance means on the first and second sides of the control rod blades, the distance means extending a distance of at least a third of the active length of the control rod blade.