Efficient decontamination technologies are needed for both decommissioning and safe operation of nuclear power plants. Up to now room walls as well as other structures contaminated with radionuclides have mainly been decontaminated using mechanical removal processes. The aim of such processes is to remove the wall surfaces to a contaminated depth of several millimeters. This generates a large amount of dust, which can lead to secondary contamination, and is associated with high personnel and/or technical expenditures. Advances in high-power lasers allow the use of laser radiation to remove contaminated layers. These layers are melted to depths of up to 5 mm by a laser beam. Most of the radionuclides are dissolved in the melt. The molten layer is detached from the wall by pulsed compressed air jets and solidifies to form small particles in which the radionuclides are fixed. The particles are then suctioned up by means of a negative pressure. The advantages of the innovative process are based on minimal dust formation and force-free coupling of the laser unit and the wall, allowing a very lightweight and flexible overall design of the system. Because the laser processes can easily be automated and controlled by remote control, the personnel exposure time within contamination areas can be minimized in an efficient manner.
The present report describes the development and testing of a laser decontamination system for the removal of radioactively contaminated concrete wall layers. A diode laser with a power of 10 kW is used as the radiation source. The laser energy is delivered via a fiber optic cable up to 100 m in length to the laser tool, which is situated on a specially designed autonomous manipulator. The manipulator moves over the wall surface to be processed by means of pneumatic suction plates. For velocities of 400 mm/min and a removal depth of 2 to 3 mm, a removal rate of 1.2 m2 per hour could be achieved. The laser focus area on the processed concrete surface is 10 mm × 45 mm. Using today’s commercially available lasers with powers of > 50 kW, removal rates higher than 6 m2 per hour are possible.
Development efforts revolving around the presented technology are focused on two main areas which can be understood as spinoffs of the present research: increasing the removal rate using more powerful lasers and adapting the technology for use in decontamination of chemically contaminated surfaces, e.g., for pollutant-free stripping of PCB-containing wall coatings.