Abstract

Thermal cutting techniques are reviewed by experiences in under water use. Experiences for oxyfuel cutting under water for depths of up to 35 m and cutting thicknesses of austenitic plated mild steel of up to 150+40 mm thickness are presented. In addition to common thermal techniques, that have found a widespread industrial use, such as plasma-arc cutting, oxyfuel cutting or laser-cutting, special techniques for decommissioning tasks, as contact-arc-metal-cutting are presented. The contact-arc-metal-cutting process has already proven its capability in decommissioning of nuclear facilities.

New trends in handling techniques aim on the reduction of time for dismantling and on reduction of time staff is exposed to radiation. A new, innovative way is to perform certain dismantling tasks manually operated, that by now had to be operated remote controlled. This approach applies if time for installation of the remote operation equipment exceeds time for the dismantling operation. Furthermore, the manually operated dismantling is much more versatile towards technical and unpredictable difficulties. A new development is e.g. the Steady-X-System which allows an operator to manipulate a tool which is designed for machine operated use. The Steady-X-System is realized by separating tool weight forces and manipulation forces, in such a way that a heavy tool may be operated manually with the required precision.

Decontamination techniques represent an important domain in the decommissioning of nuclear facilities. By decontamination, radioactivity of components may be drastically decreased, so that further treatment may occur at much lower security standards, or the component may even be disposed or recycled conventionally. By this means, an important reduction of radioactive waste and therefore reduction of costs can be achieved. The scope for waste reduction is enormous high for mineral (concrete) and ceramic components. As state of the art in decontamination, mechanical methods, such as milling, sandblasting, hammer, scabbier or needle-sealer are most commonly used to remove the contaminated surfaces and activated layers of concrete components. One disadvantage of these techniques is, that removed, radioactive particles are partially reintegrated by the mechanical action into the new generated material surface. To eliminate this recontamination, additional material has to be removed and disposed as radioactive wastes, than necessary if recontamination could be avoided. New technologies able to remove surfaces from ceramic and mineral materials are to be developed. One novel technique which is presented here is the dryice laserbeam process. A laserbeam heats the surface of the material to be removed at exactly controlled temperatures. Dryice pellets, consisting of compressed carbon dioxide snow at phase equilibrium solid–gas at −78 °C, are subsequently projected onto the heated surface. Multiple mechanisms effect the removal of the materials surface. The removed surface layer is sucked off with the gaseous carbon-dioxide. Recontamination hardly occurs. Surface removal by dryice-laser beam-process may be effected on concrete and on ceramic surfaces, where removal-precision in between 0,5 and 2 mm is reached as well as on organic coating with very good bonding as e.g. powder coatings.

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