Nuclear Reactor Nozzle Repair Without Heat Treatment
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Solution Overview
Problem
The existing nozzle repairing methods for nuclear reactor vessels require heat treatment to remove stress after welding, which is challenging in high-radiation areas, and do not effectively improve stress corrosion resistance.
Innovation Solution
A method that involves removing the first connection portion of the in-core instrument tube, grooving the second connection portion, inserting a new in-core instrument tube, and groove-welding it without heat treatment, using a material with higher stress corrosion resistance, and performing buttered welding to cover the existing groove-welding portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire groove-welding portion is removed and restored, then the stress corrosion resistance is improved, but the workability deteriorates due to the need for heat treatment in high-radiation areas
Solution Approach 1:
The groove-welding portion is divided into two separate connection portions (first connection portion and second connection portion). Only the first connection portion is removed and restored, while the second connection portion is left intact. This segmentation allows the repair to be performed without removing the entire groove-welding portion, thereby avoiding the need for heat treatment and improving workability while still enhancing stress corrosion resistance through the restoration of the first connection portion.
2Reliability
If heat treatment is performed after welding to remove stress, then the reliability is improved, but the ease of operation deteriorates due to the difficulty of performing heat treatment in high-radiation areas
Solution Approach 1:
The harmful effect of stress is eliminated by selectively removing only the first connection portion that contains the stress, rather than performing heat treatment on the entire groove-welding portion. The second connection portion is preserved and used as a stable base that does not require heat treatment, thereby extracting the stress removal function from the heat treatment process and enabling repair without heat treatment in high-radiation areas.
3Reliability
If the groove-welding portion is completely removed and restored, then the stress corrosion resistance is improved, but the loss of time increases due to the extensive repair process
Solution Approach 1:
The repair is applied locally only to the first connection portion where stress corrosion cracking is most likely to occur, rather than restoring the entire groove-welding portion. The second connection portion is left intact and serves as a stable reference structure. This local quality approach concentrates the repair effort where it is most needed, reducing the overall repair time while still achieving improved stress corrosion resistance.
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 allows for easier and more effective nozzle repairs without the need for heat treatment, improving workability and stress corrosion resistance by using a new groove-welding portion with higher stress corrosion resistance.
Implementation Method 1
groove-welding the inner surface side of the semi-spherical portion so as to fix the new in-core instrument tube
Implementation Method 2
performing buttered welding to cover the existing groove-welding portion
Data Source
AI summary
It is possible to improve the workability and the stress corrosion resistance by easily performing a repairing operation in a nozzle repairing method and a nuclear reactor vessel. The repairing method includes: removing a first connection portion ((trepanned portion) 208) with respect to an in-core instrument tube (204) in a groove-welding portion (206); removing the in-core instrument tube (204) from a lower mirror (66); leaving and grooving a second connection portion ((existing welding portion) 211) with respect to the lower mirror (66) in the groove-welding portion (206); inserting a new in-core instrument tube (204A) into an attachment hole (203); and groove-welding (so as to form a new groove-welding portion (213)) the inner side of the lower mirror (66) so as to fix the new in-core instrument tube (204A).