Boiling Water Reactor Control Rod with Segmented Cruciform Blades
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Solution Overview
Problem
Control rods in boiling water reactors face degradation due to Irradiation Assisted Stress Corrosion Cracking (IASCC) and have poor seismic scrammability, which is critical for reactor safety during earthquakes, especially when structural rigidity hinders quick reactor shutdown.
Innovation Solution
A control rod design with a cruciform cross-section structure that separates blades into distinct regions with different cross-sectional configurations, including a first region with a united cruciform cross-section, a second region with separated cross-sections, and a third region with continuous and separated blades, reducing crevice formation and enhancing flexibility during seismic events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the control rod uses a rigid structure with united cruciform cross-section to maintain structural integrity, then structural strength is improved, but seismic scrammability deteriorates
Solution Approach 1:
The control rod is divided into multiple blade members (first through fourth blade members) that can separate from each other during seismic events. The separation regions allow blades to move independently, improving scrammability while maintaining structural integrity when united during normal operation.
Solution Approach 2:
The control rod structure transitions from a static rigid configuration to a dynamic configuration during seismic events. The blades can separate and move relative to each other, allowing the structure to adapt to seismic forces while maintaining strength during normal reactor operation.
2Ease of manufacture
If the control rod uses a structure with crevices between blades to reduce manufacturing complexity, then ease of manufacture is improved, but reliability deteriorates due to IASCC
Solution Approach 1:
The design extracts and eliminates the harmful crevice spaces between blades by providing substantial contact surfaces where blades directly touch each other. This removes the crevice corrosion pathway while maintaining the simplified blade structure for easy manufacturing.
Solution Approach 2:
The design converts the potential harm of blade separation into a benefit by designing substantial contact surfaces that prevent crevice formation. The same structural features that enable blade separation also eliminate crevices, turning a potential reliability issue into a solution.
3Speed
If the control rod uses separated blade cross-sections to enhance flexibility during seismic events, then seismic scrammability is improved, but structural strength deteriorates
Solution Approach 1:
The control rod is segmented into multiple blade members with defined separation regions. During seismic events, blades can separate to improve scrammability, while the segmented structure maintains overall structural integrity through the connection regions between blades.
Data Source
AI summary
A control rod for a boiling water reactor is provided with a structure element having mutually-perpendicular four blades. The four blades have a neutron absorber-filling region that neutron absorber is held, respectively. In the structure element, a plurality of regions formed in an axial direction of the control rod include a first region having a first cross-section that forms a first united cruciform cross-section of the four blades connected one another, a second region having a second cross-section that has each separated cross-section of the four blades, and a third region having a third cross-section that has a second united cross-section of continuous two blades of the four blades, disposed in a diametrically opposite direction and facing each other and each separated cross-section of remaining two blades of the four blades, disposed perpendicularly to the continuous two blades.