Two-Piece Replacement Nozzle for Nuclear Reactor Coolant Piping
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Solution Overview
Problem
Nozzle failures and leakage in nuclear power facilities due to stress corrosion cracking, particularly in pressurized vessels and reactor coolant piping, result in lengthy repair schedules and increased radiation exposure for personnel, as existing one-piece replacement nozzle methods require large structural weld joints.
Innovation Solution
A two-piece replacement nozzle design, comprising a thin-walled first nozzle piece inserted into a counterbored opening and a smaller weld pad, with a second nozzle piece welded internally, reducing the size of weld pads and joints, allowing for faster installation and reduced radiation exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-piece replacement nozzle is used, then the nozzle can be replaced with a single component, but the weld pad and pad-to-nozzle weld become relatively large, resulting in long welding schedule duration and increased personnel radiation exposure
Solution Approach 1:
The replacement nozzle is divided into two separate pieces: a first replacement nozzle portion that interfaces with the weld pad, and a second replacement nozzle portion that connects to the existing instrumentation piping. This segmentation allows the weld pad to be minimized in size while still accommodating the full functional requirements of the original nozzle, thereby reducing welding time and radiation exposure.
2Strength
If a one-piece replacement nozzle is used, then the nozzle maintains structural integrity, but the large weld joint geometry increases the risk of welding issues and requires more material
Solution Approach 1:
By segmenting the nozzle into two portions, the weld pad size is reduced, which directly decreases the volume of material exposed to radiation and the potential for welding defects. The first nozzle portion is welded to a minimized weld pad, and the second portion is welded to the existing piping, distributing the welding operations and reducing overall risk.
Solution Approach 2:
The second replacement nozzle portion is positioned within or adjacent to the first portion, creating a nested or closely integrated configuration. This allows the replacement assembly to maintain the external dimensions and structural profile of the original nozzle while using a minimized weld pad, thereby preserving structural integrity without the harmful effects of large weld joints.
3Ease of repair
If a one-piece replacement nozzle is used, then installation is straightforward, but the repair time and outage duration are significantly increased
Solution Approach 1:
The segmented nozzle design allows the first portion to be installed with a minimized weld pad, which reduces welding time. The second portion can be separately prepared and attached, allowing parallel preparation activities and reducing overall repair duration while maintaining ease of installation through modular assembly.
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 two-piece nozzle design significantly reduces the time required for replacement, minimizing outage duration and personnel radiation dose by approximately half, while maintaining the same dimensions and functionality as the original nozzle.
Implementation Method 1
A two-piece replacement nozzle design, comprising a thin-walled first nozzle piece inserted into a counterbored opening and a smaller weld pad, with a second nozzle piece welded internally
Data Source
AI summary
This invention provides an improved replacement nozzle configuration. The nozzle is provided in two pieces. A first nozzle piece is a relatively thin-walled cylinder that is inserted into the counterbored opening of a pressure vessel after the protruding portion of the original nozzle has been removed. A weld pad is attached to the pressure vessel, to which the first replacement nozzle piece is welded. Due to the reduced dimensions of the thin-walled first nozzle portion, a much smaller weld pad and pad-to-nozzle weld can be used. A second nozzle piece is positioned within the first nozzle piece and welded thereto. The existing instrumentation piping is connected to the free end of the second nozzle piece. This two-piece replacement nozzle can be implemented in approximately half the time required for the one-piece design.