EDM In-bore System (Thermal Tube Cutting )

A Novel Approach to Foreign object Management in SG Tubes(16.9Ø)

 Steam generator maintenance is conducted periodically, and owing to advancements in inspection technologies, there is a growing incidence of identifying extraneous materials within the steam generator structure.

 We propose a miniature in-bore Electrical Discharge Machining (EDM) system designed for the safe removal of foreign materials located around the SG tubes within a nuclear power plant's steam generator. Targeting specific regions near the U-BEND, this system employs EDM technology to remotely and automatically create a passage window in the SG heat exchange tube for the removal of foreign objects. This is achieved without causing additional mechanical stress on the SG tube, ensuring a stable passage for the removal of foreign objects from the secondary side. Additionally, this in-bore EDM system allows for remote handling, which minimizes radiation exposure for nuclear workers.

 This end- tool, equipped with ultra-miniaturized in-bore EDM technology and designed with an optimal electrode in terms of size and shape, can be inserted through the primary side tube sheet of the SG tube to accurately reach the target location. It ensures the removal of the foreign object without generating additional materials and safely exits to the steam generator's primary side water chamber. Pipe blocking service can be provided in conjunction with.

EDM End tool
-Linear/Lateral/Curved

This equipment, functioning as the distal end device where discharge machining is actually carried out, facilitates the occurrence
of discharges between the electrode at the top of the device and the workpiece (inner wall of the thermal tube). As a result, it can create openings in the steam generator's thermal tube.

Once the rotational angle adjustment is completed, the lower device's fixation component is activated, attaching an O-ring to the inner wall of the thermal tube, securely anchoring the device to the thermal tube's inner wall. During the supply of discharge machining fluid, the electrode undergoes reciprocating motion, generating discharge debris of 100μm or less. This process results in the formation of openings.

• Linear : The distal end device performs linear reciprocating motion in the direction of the thermal tube's conduit.

• Lateral : The distal end device performs diagonal reciprocating motion in the direction of the thermal tube's conduit

• Curved : The distal end device performs a diagonal reciprocating motion in the lateral direction of the thermal tube's conduit in a bending configuration. In the case of the bending configuration, it is possible to enter both the U-bend region and the fully curved section of the steam generator's thermal tube. The length of electrode disengagement from the thermal tube is structurally determined by the machining, which enhances the likelihood of preserving foreign materials. Additionally, even in the event of power loss, there is a possibility of manually retracting the device from the interior to the exterior of the thermal.

 

EDM
power and motion controller

• Motion C-Box(Controller Box)
 EDM motion control unit can control the position and orientation of various robots ranging from 1 to 6 axes, and it is customized to enhance the efficiency of discharge machining and optimize the versatility of robot movement range in
line with customer requirements.

• Power C-Box(Controller Box) 
 The output of the power control unit determines the maximum power capacity that can be exerted within the given environment, considering the discharge machining area and volume required by the customer.

EDM
Puller and Pusher

• EDM Puller
 The EDM Puller can spool up cables connected to the EDM END tool up to a maximum length of 25 meters. It maintains real-time tension on the spooled cable to prevent detachment. Additionally, the borescope used for discharge machining
position adjustment can also be wound up in a similar manner.

• EDM Pusher
 The EDM Pusher plays a crucial role in transporting the EDM END tool to the target location. The EDM END tool, attached to the cable, is inserted into the interior of the thermal tube. It is then moved forward and backward by four interlocking rollers, achieving a minimum repeat precision of 1mm during the movement.

EDM 
Assistance Software

• EDM Control S/W
The program that directly controls the real-time functions related to discharge machining includes the EDM END tool's position movement and fixation, the supply of discharge machining fluid, the operation of EDM Puller and EDM Pusher, the initiation of discharge machining processes, and the configuration of various discharge machining parameters such as current, gap voltage, electrode speed, etc. Additionally, it enables real-time monitoring of discharge machining efficiency and discharge parameters by recording data separately, and visually presenting it in the form of graphs.

Development program: PLC(Programmable logic controller), CIMON

• EDM Positioning S/W
 This is a position calculation program that quantitatively calculates the current position (height) from the reference point of the EDM END tool inserted inside the thermal tube, as well as the angle from the reference point of the electrode's front end (in the direction of movement). This program provides information to completely control the equipment's position in hidden areas remotely, ensuring precise control of the device's location.

Development program: Labview

• EDM Boat Sampling S/W
The dedicated software used during boat sampling operations has several functions. It allows you to adjust discharge process variables to control power, control camera positions, regulate the flow rate of the circulation system, and control the actuators of the underwater EDM discharge device to manage motion. The motion control of actuators involves measuring the gap between the discharge electrode a d the workpiece precisely and controlling motor rotation speed accordingly. This allows operators to conduct safe, remote boat sampling operations.  All of this software is registered with the Korean Copyright Commission and is available exclusively through KNR.

---

---