Particle Release During Laser Decontamination of Concrete Surfaces

The phase–out of all Nuclear Power Plants (NPP) until 2022 in Germany offer the opportunity to apply new and efficient decommissioning technologies, which allow further reduction of decommissioning costs and minimization of the collective dose for personnel. One challenging task in this process is the decontamination of protective paints containing polychlorinated biphenyl (PCB). PCB-containing surfaces demand consecutive radiological decontamination and removal of the PCB-containing paints before the demolition is possible. Laser technology, commonly used in many different industrial sectors, presents an advanced approach to this problem. Successful thermal decomposition of PCB-containing paints using high power diode lasers has been reported by our group in former publications [1]. Ongoing investigations focus on the technology transfer from static laboratory state to industrial application. This includes the verification of safety and efficiency issues for the complete laser supported process. The current presentation covers all aspects of the laser process: concrete sample preparation as well as an experimental set-up utilizing a mobile laser system that includes an innovative laser head. Particular focus will be on the phenomena of the generated concrete surfaces and the arising by-products during laser processing. A 10 kW high power diode laser, Laserline LDF 1500-10000 was used for the ablation experiments. Concrete samples were coated with typical decontamination epoxy-based paints, which match the commonly used paint systems in German NPPs in terms of composition, structure and thickness. The influence of significant processing parameters (laser power, feed rate, type of concrete and composition of paint) on the laser ablation are shown in relation to the energy input per length. The release of particles is subjected to these parameters as well. Therefore the size and the shape of the arising particles have been measured online in accordance with these processing parameters by an Engine Exhaust Particle Sizer (EEPS, Model RP-3090, TSI) in a range between 5.6 to 560 nm. The quantity of particles has also been counted by a Condensation Particle Counter (CPC, Model 3022, TSI). Overall up to 6 million particles per cubic decimeter are detected with a dilution factor of 1:100 throughout the experiments. Both measuring systems are connected to the exhaust air pipe downstream, next to the laser head. The shift of the particle size in accordance with the above mentioned parameters is crucial for a comprehensive understanding of the laser decontamination. The mobile laser supported decontamination technology will be tested in 2018 in a German nuclear facility. This test will contain the decontamination process with actual surface configurations like floors, walls, ceilings and corners, and will act as an effective proof-of-concept for the developed laser system prototype.