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DEVELOPMENT OF A PLASMA ARC TORCH AND CONTROL/MONITORING TECHNIQUE FOR THE INTERNAL CUTTING OF SMALL BORE PIPEWORK

Objective

During decommissioning of nuclear facilities, small bore pipework needs to be cut remotely up to distances of 10m with access through the top of the pile cap. Often, due to the close packing of the pipework, the cutting operation must be performed internally through the bore of the tube. In the absence of direct viewing and manual access, there is a requirement to develop techniques for the cutting process and methods for monitoring and remotely controlling its operation and ensuring its effectiveness. The plasma torch process has been selected as the cutting method based on economic considerations and on its reliability and effectiveness in remote and manual operations.

The objective of the project is to develop:

techniques based on non-contact sensors which can monitor and remotely control the progress and effectiveness of the cutting process;
a small plasma torch capable of being inserted in the bore of < 50 mm internal diameter pipework with remote deployment (up to 10 m distance) under automatic control;
the deployment system which can be located on the pile cap, positioned above each pipe in turn and lowered to a predetermined depth to perform a complete circumferential severance of the tube in one pass.

The work will include cutting trials of the complete system in a full-size mock-up of a reactor gas manifold.

The AEA Northern Research Laboratories will take into account the experience gained elsewhere and particularly at the "Institut fuer Werkstoffkunde der Universitaet Hannover" on plasma arc torch cutting and its control/monitoring.
During decommissioning of nuclear facilities, small bore pipework needs to be cut remotely up to distances of 10 m with access through the top of the pile cap. Often, due to the close packing of the pipework, the cutting operation must be performed internally through the bore of the tube.

The objective of the project is to develop:
techniques based on non contact sensors which can monitor and remotely control the progress and effectiveness of the cutting progress;
a small plama torch capable of being inserted in the bore of less than 50 mm internal diameter pipework with remote deployment (up to 10 m distance) under automatic control; the deployment system which can be located on the pile cap, positioned above each pipe in turn and lowered to a predetermined depth to perform a complete circumferential severance of the tube in one pass.

The remote deployment system has been designed, manufactured, commissioned and operated on the reactor using the specially adapted plasma torch. The deployment rig was used to locate the plasma torch at distances of up to 1 metres. A specially developed camera system was used to carryout the remote inspection of the stay tubes. Full mock-up tests have been completed and operators fully trained on using the equipment. A total of 130 tubes were successfully cut and inspected. The first stage of the control software has been completed and a small test rig constructed to test the software.
WORK PROGRAMME

1. Literature survey to find the most suitable plasma cutting combination for this application.

2. Torch adaptation for remote deployment and automatically controlled rotation

3. Examination of the cutting parameters on representative pipework.

4. Control system developments; monitoring technique and feedback system will be designed, developed and interfaced for automatic control.

5. Preliminary testing of the deployment system in small-size mock-up

5.1. To test the workability of the remote deployment system.
5.2. To check the feedback control system under remote operation conditions.
5.3. To optimize the equipment to commercial standards.

6. Testing of the deployment system in full-size mock-up to evaluate the optimized system in a representative decommissioning environment.

7. Final evaluation including specific data on costs and radiological impact on work force and working area, working time and secondary waste arisings.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

United Kingdom Atomic Energy Authority (UKAEA)
Address
Sellafield Laboratory
CA20 1PF Seascale
United Kingdom