Control Rod Drive Seal Rewelding for Reactor Maintenance
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Solution Overview
Problem
Existing methods for maintaining rod assembly control mechanisms (MCGs) in nuclear reactors, such as the 'Canopy' and 'Omega' RMCG solutions, are unsatisfactory due to high complexity, unpredictable defects, and the need for complete replacement of components, which disrupts planning and dosimetry.
Innovation Solution
A method involving the removal of lips forming the omega seal, machining the casing upper end, and creating a leak-tight welded connection between the casing and sheath, allowing for selective replacement of the EML and sheath without removing the heat-insulation, thereby reducing defects and simplifying the maintenance process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the complete MCG is replaced by intervening at the Canopy seal, then the rod assembly control mechanism can be maintained, but the heat-insulation of the cover must be removed and refitted which disrupts planning and increases time loss
Solution Approach 1:
The invention divides the maintenance operation into two separate access points: the Canopy seal for EML replacement and the Omega seal for sheath replacement. This segmentation allows selective maintenance of components without requiring complete MCG replacement or heat-insulation removal, thereby reducing time loss and planning disruption while maintaining reliability.
2Ease of manufacture
If the Omega seal is cut vertically to preserve the initial design, then the welded seal design is maintained, but unpredictable surface defects appear in 38% of cases requiring systematic repair
Solution Approach 1:
The invention removes the lips forming the Omega seal before welding, thereby eliminating the source of surface defects in advance. This preliminary action prevents the formation of defective zones that would otherwise require systematic repair, while still achieving a leak-tight welded connection between the casing and sheath.
3Reliability
If the lips forming the Omega seal are removed and a new welded connection is created, then leak-tightness is achieved without unpredictable defects, but additional machining operations are required
Solution Approach 1:
The invention extracts and removes the lips forming the Omega seal, which are the source of unpredictable surface defects. By taking out these problematic components, the invention eliminates the defect source while requiring only standard machining operations to create fresh welding surfaces, achieving leak-tightness without defects.
4Loss of time
If selective replacement of EML and sheath is performed without removing heat-insulation, then time is saved and planning is simplified, but access to the Omega seal becomes more difficult
Solution Approach 1:
The invention segments the maintenance access points by enabling intervention at the Omega seal independently of the Canopy seal and heat-insulation removal. This segmentation provides direct access to the sheath and EML through the Omega seal location, saving time and simplifying planning while avoiding the complexity of heat-insulation removal.
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
This method ensures reliable and economical maintenance by eliminating defects, saving time, and minimizing disruptions to reactor operations while maintaining leak-tightness without unnecessary component replacement.
Implementation Method 1
creating a leak-tight welded connection between the casing and the sheath or a replacement sheath, by welding the welding surface and a matching welding surface provided at the sheath lower end
Data Source
AI summary
A maintenance method is applied to a nuclear reactor having a drive assembly for a control rod assembly. The drive assembly includes a casing for receiving a drive rod lifting mechanism and a sheath for receiving the drive rod. A first lip is at an upper end of the casing, and a second lip is at a lower end of the sheath. The lips are welded together forming a seal between the casing and said sheath. The method includes removing the lips via material removal; carrying out a maintenance operation on the control rod assembly; creating a welding surface by machining the upper end of the casing; and creating a leak-tight connection between the casing and the sheath by welding the created welding surface to a matching welding surface provided at the lower end of the sheath. A replacement sheath may be used instead of the original sheath.