Adaptive CRDM Bolt Drilling Assembly for Stuck Thread Extraction
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Solution Overview
Problem
In boiling water nuclear reactors, stuck bolts due to galled threads between stainless steel bolt and flange interfaces pose challenges during maintenance, leading to prolonged exposure to radiation, high costs, and compromised vessel integrity, with conventional solutions being risky, cumbersome, and inefficient.
Innovation Solution
An adaptive drilling device with a guide assembly, drill assembly, and thrust assembly is designed to safely and efficiently extract and rethread bolts in the control rod drive mechanism, utilizing a gear reduction drive motor, drill bearings, and a securing subassembly to align and secure drilling activity, and a thrust handle connected to a lead screw for linear movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional improvised processes and machines are used to extract stuck bolts, then extraction can be performed, but the process becomes risky, heavy, cumbersome, and dangerous with prolonged radiation exposure
Solution Approach 1:
The device is divided into distinct functional modules: a guide assembly with guide plates and rods for positioning, a drill assembly with motor and drill bit for bolt removal, and a thrust assembly with lead screw and feed wheel for controlled movement. This segmentation allows each component to perform its specific function efficiently while reducing overall operational complexity
Solution Approach 2:
The guide assembly acts as an intermediary between the operator and the drill assembly, providing precise alignment and positioning. The guide plates and rods serve as mechanical mediators that constrain the drill bit to follow a predetermined path, eliminating the need for complex manual positioning and reducing operator exposure to radiation
2Productivity
If conventional extraction methods are used, then bolts can be removed, but extraction time increases leading to higher labor costs and excessive radiation dose
Solution Approach 1:
The guide assembly is pre-configured with guide plates and rods positioned to align with the bolt locations before the extraction process begins. This preliminary positioning eliminates the need for time-consuming alignment adjustments during operation, allowing immediate drilling upon activation and significantly reducing total extraction time
Solution Approach 2:
The manual mechanical process of aligning and positioning extraction tools is replaced by the pre-configured guide assembly with fixed guide plates and rods. This mechanical guidance system automatically ensures proper alignment, eliminating the time-consuming manual positioning that characterized conventional methods
3Reliability
If stuck bolts are not properly extracted and re-threaded, then maintenance can proceed, but vessel integrity is compromised
Solution Approach 1:
The guide assembly provides localized precision positioning at the exact locations where bolts need to be extracted and re-threaded. The guide plates and rods are positioned to ensure accurate alignment specifically at the critical threaded areas, maintaining vessel integrity without requiring complex global repositioning systems
Solution Approach 2:
The device enables precise control over drilling parameters through the thrust assembly's lead screw mechanism, allowing adjustment of feed rate, depth, and pressure. This parameter control ensures that the drilling and re-threading process maintains optimal conditions for preserving vessel integrity while managing repair complexity
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 device reduces radiation exposure time, minimizes labor costs, and maintains vessel integrity by allowing faster and more precise extraction and rethreading of stuck bolts, thereby enhancing safety and efficiency during maintenance.
Implementation Method 1
a lead screw running through the central plate nut and connected to the thrust handle
Implementation Method 2
a gear reduction drive motor
Implementation Method 3
a drill bit, and a securing subassembly configured to secure the drill assembly to a first guide plate
Data Source
AI summary
An adaptive drilling device for extracting bolts from a control rod drive mechanism (CRDM) in a boiling water nuclear reactor includes a guide assembly configured to align and secure drilling activity, a drill assembly configured to drive a drill bit into a CRDM bolt, and a thrust assembly configured to linearly and bidirectionally drive the drill assembly. The guide assembly has three guide plates and a pair of guide rods. The drill assembly includes a gear reduction drive motor, drill bearings, a drill bit, and a securing subassembly configured to secure the drill assembly to a first guide plate. The thrust assembly includes a thrust handle connected to the drive motor, a central plate nut, a lead screw running through the central plate nut and connected to the thrust handle, and a feed wheel connected to the lead screw.