Nuclear Fuel Assembly Channel Box Protrusions
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Solution Overview
Problem
Shadow corrosion on zirconium-based channel boxes in nuclear boiling water reactors leads to channel box bowing, causing interference with control rods and potential fuel assembly lifting due to close contact with stainless steel control rod blades, exacerbated by manufacturing and irradiation-related elongation.
Innovation Solution
The fuel assembly design features protrusions along the full length of the channel box's outer sides, increasing the distance between the channel box and control rods, which mitigates shadow corrosion and ensures smooth control rod insertion, with protrusions distributed evenly and curved to facilitate sliding, and a cruciform support member for added rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the channel box is made close to control rods to maximize fuel assembly space, then space utilization is improved, but shadow corrosion occurs leading to channel box bowing and control rod interference
Solution Approach 1:
Protrusions are introduced as intermediary elements between the channel box and control rod. These protrusions maintain a controlled gap that prevents direct contact, thereby eliminating shadow corrosion while still allowing the channel box to be positioned close to the control rod for optimal space utilization.
Solution Approach 2:
The protrusions are designed in advance to prevent shadow corrosion before it can occur. By maintaining a predetermined gap through the protrusions, the harmful shadow corrosion effect is prevented from initiating, avoiding subsequent channel box bowing and control rod interference.
2Object-affected harmful factors
If protrusions are added to channel box outer sides to prevent shadow corrosion, then shadow corrosion is reduced, but device complexity increases
Solution Approach 1:
Instead of modifying the entire channel box structure, protrusions are added only at specific local positions on the outer sides where shadow corrosion would occur. This localized modification effectively prevents shadow corrosion while minimizing the increase in overall device complexity.
3Ease of manufacture
If the channel box is allowed to deform under irradiation, then manufacturing flexibility is improved, but channel box bowing increases causing control rod interference
Solution Approach 1:
The protrusions serve as a cushioning mechanism that compensates for channel box deformation due to irradiation. By maintaining a gap through the protrusions, the design accommodates shape changes while preventing the channel box from bowing into contact with the control rod, thus maintaining stability in the operational relationship.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces shadow corrosion and channel box bowing, preventing control rod interference and ensuring reliable fuel assembly operation by maintaining a consistent gap between the channel box and control rods, thereby reducing the risk of fuel assembly lifting.
Implementation Method 1
Shadow corrosion is a local corrosion enhancement and can appear on a zirconium based alloy component when the component is in close contact with another metal
Implementation Method 2
the protrusions are configured to enable a control rod to easily slide over and on top of them
Data Source
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AI summary
A fuel assembly (3) for a nuclear boiling water reactor (1) is provided. The reactor comprises a plurality of such fuel assemblies and a plurality of control rods (4). Each control rod is insertable between the fuel assemblies. The fuel assembly has a longitudinal center axis (z) and includes a plurality of elongated fuel rods (7) and an elongated channel box (6). The channel box has inner sides (8), facing the fuel rods, and outer sides (9). Each inner and outer side has a longitudinal center line (y) extending in parallel with the center axis and along the length of the channel box. A number of protrusions (12) are distributed along the center line of at least two of the outer sides. The protrusions are configured to ensure a minimum distance (d2) between the outer side and an adjacent control rod and to enable the control rod to easily slide over and on top of the protrusions.