atw - International Journal for Nuclear Power | 11/12.2019

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atw Vol. 64 (2019) | Issue 11/12 ı November/December DECOMMISSIONING AND WASTE MANAGEMENT 546 | Fig. 6. Overview of tested samples as supplied by KTE (A– lid of a 200 liter drum, B– steel sheet, C– coated u profile, D– locker door part). | Fig. 7. Components for decontamination of complex metal surfaces, (A) laser tool for the decoating of flat surfaces and (B) laser tool for the decontamination of edges. transported using optical fibres to reach the experimental area. This feature allows for the protection of costly laser equipment from contamination in any case, as described in section 2. The user can simply equip the required laser tool and start the decontamination process. Suction and filtration of mobilized contamination at high efficiency is facilitated applying a commercial filtration and suction unit by ULT GmbH. The localized suction of aerosols leads to prevention of recontamination and guarantees clear vision for the user at all times. Restricted access to the experimental area is beneficial to simplify the laser safety requirements, even in case of a technology demonstration. A full-fledged risk assessment according to §5 of ArbSchG [18] and §3 of ArbStättV [19] has been filed to scan for any arising risks for operators coming along with the application of the whole set up. All requirements of the occupational safety have been tested and proven. The risk assessment covers the following subject area: p General occupational safety p Laser safety p Safety from toxic substances (PCB) p Radiation safety p Respiratory protection The risk assessment complies with the laws, guidelines (ASR), workers compensation board rules and provisions. The risk assessment was finalized by TU Dresden and IABG and checked by KTE and has been the fundamental milestone for approval of the on-site demonstration at MZFR. 5.3 Decontamination of complex metal geometries The decontamination of metal surfaces at MZFR was conducted on paints and metals prior unknown, to check the ability to transfer results from laboratory scale to on-site tests. To test limits of the laser tool, samples of varying geometries have been supplied by KTE, e.g. painted steel sheets, bracket steel or complex surfaces like ridges/spline/serration, as shown in Figure 6. Different laser tools were designed to ensure the decontamination at different surface geometries, e.g. in case of tighter angles the tool was adapted to maintain the complete suction of particles and aerosols during the laser process. A tool change can be completed within 1.5 min, Figure 7. Similar ablation characteristics were found for all tested samples as compared to the laboratory results (Figure 2). This implies that generalized material characteristics for paint layers and metals can be applied. From practical point of view, the flexibility of the laser ablation process was verified, as all tested geometries were completely cleaned without residues (Figure 8). 5.4 Decontamination of concrete walls and floor at MZFR Decontamination of concrete demands solutions for a multitude of demands, e.g. uneven surfaces, varying thicknesses of paint, different shapes of surfaces and unknown PCB concentration in the decontamination paint. The practicability of the developed laser system was tested on walls and floors at the MZFR on sample surfaces sized 30 x 30 cm². The decontamination paint on the wall was thin and exhibited a high PCB concen tration (see Table 3). The floor featured lower PCB concentration and very thick paint (approx. 1.5 mm). In Figure 9 the side view of the laser head is shown during the decontamination. During the process all arising by-products, like visible particles and gases, are extracted by the extraction and filtration unit and do not endanger the working staff. Figure 10 displays the result of decontamination on a floor | Fig. 8. Steel sheet partly decoated. | Fig. 9. Laser head during the decontamination of the floor. Decommissioning and Waste Management First On-site Demonstration of Laser- based Decontamination Technology in Germany ı Torsten Kahl, Georg Greifzu, Carsten Friedrich, Christian Held, Marion Herrmann, Wolfgang Lippmann and Antonio Hurtado
atw Vol. 64 (2019) | Issue 11/12 ı November/December | Fig. 10. Demonstration field floor (A) before and (B) after the decontamination with multiple scans. Sample number Position Before decontamination PCB in mg/kg demonstration field before (A) and after (B) the laser process. In Figure 11 the laser head is displayed with different adaptions for flat areas (picture A and B) and internal corners (picture C). The modular set-up enables a fast change of the adaptions omitting any changes to the leaser heads basic components. Using such adaptions the decontamination of a wall with adjoining corners was demonstrated, illustrating the clear advantage compared to shaving equipment, where usually boundary areas need an additional, time- consuming handling step. The removal of thick layers and/or remaining soot can be realized by multiple passes. Both have been demonstrated in Karlsruhe. During the demonstration an average laser power of 3.7 kW was applied, resulting in a practical determined ablation speed of 6 m²/h 5.5 PCB sampling at the MZFR Within the demonstration PCB sampling was performed to prove the decontamination rate of the laserbased paint removal. This study aimed at the evaluation of the PCB concentration of the primary source. To release material the PCB-concentration must amount less than 50 mg/ kg. Samples with mass > 50 mg were extracted using an electric scraper. AGROLAB Labor GmbH performed the analysis of the samples according to DIN EN 15308. The samples taken before the decontamination consisted mainly of decontamination paint. After the decontamination no paint remained on the surface anymore, therefore the now surfacing concrete was sampled. In Figure 12 the sampled surfaces are shown before PCB sampling (A), after PCB sampling (B) and after decontamination and the consecutive PCB sampling (C). The corresponding PCB concentration is shown in Table 3. The laser-based decontamination process resulted in an average reduction of PCB of 98.7 % within a practical application. This value is even higher than the value of the laboratory experiments performed at the TU Dresden [16]. The remaining PCB concentration after the decontamination is mainly caused by the PCB inside the concrete matrix. After sealing the walls with PCB containing paint the PCB diffuses from the decontamination paint (primary source) into the concrete. Alternative laserbased technologies are available to remove and to vitrify concrete surfaces in a single process step [20; 21]. | Fig. 11. Laser head for concrete decontamination; A- laser head (round version), B- laser head (angled), C- laser head internal corner. After decontamination PCB in mg/kg Difference mg/kg | Fig. 12. Examples of a demonstration field: (A)- before sampling, (B)- after decontamination and (C)- after decontamination and sampling. 6 Conclusion and future prospects The TU Dresden successful demonstrated the application of laser-based decontamination on radiologic and chemical-toxic contaminated metal and concrete surfaces at the MZFR in Karlsruhe. All necessary documents to obtain acceptance of the KTE were prepared by TU Dresden and approved by KTE. An independent work permit was available to TU Dresden. The selective decontamination on metal surfaces is characterized by a process stop after removing any coating (decontamination paint, oxide and/or contamination). The practical removal rate on metal is 0.42 m²/h using a mean laser power of 150 W and an average paint thickness of 165 µm. The application of laser-based decontamination to PCB-contaminated concrete surfaces resulted in a mean reduction of 98.7 % of the PCB-concentration. During the onsite-demonstration a removal rate of 6 m²/h of paint from concrete walls with 3.7 kW laser power were accomplished. The handheld laser tools Reduction % 1 Floor 9.3 0.23 9.07 97.5 2 Floor 30.1 0.04 30.06 99.9 3 Wall 3,810 67.3 3,742.7 98.2 4 Wall 2,360 19 2,341 99.2 5 Wall 1,976 18.9 1,957.1 99.0 6 Wall 2,510 14.2 2,495.8 99.4 7 Wall 2,272 49.7 2,222.3 97.8 | Tab. 3. PCB concentration of the sampling before and after the decontamination. Ø 98.7 % DECOMMISSIONING AND WASTE MANAGEMENT 547 Decommissioning and Waste Management First On-site Demonstration of Laser- based Decontamination Technology in Germany ı Torsten Kahl, Georg Greifzu, Carsten Friedrich, Christian Held, Marion Herrmann, Wolfgang Lippmann and Antonio Hurtado
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