DISMANTLING LARGE COMPONENTS | DECOMMISSIONING
V Post-segmentation The separated ring segments are placed on the reactor building operation floor or on the reactor pool bottom. The location of the post-segmentation area depends primarily on the possibilities and conditions on site and the resulting space conditions. The reactor building crane is used to transport the cut ring segments of the RPV to the post-segmentation area. The pre-segmentation design ensures that the maximum weight of the RPV segments, in particular that of the RPV calotte, does not exceed the permitted operational load capacity of the reactor building crane. At the post-segmentation area, the post-segmentation
into smaller segments suitable for packaging begins. At the same time, the preparatory work is started for cutting off the next ring segment of the RPV. The segmentation equipment includes a rotating
cutting table and a cutting robot with an attached oxyacetylene torch. The packages are placed into packaging containers provided by the customer. As in the case of pre-segmentation, cutting at the post-segmentation area is carried out remotely by means of thermal cutting techniques. The thermal cutting process is a proven cutting
technology in the conventional dismantling of large components. In nuclear facilities, the spread of contamination by cutting fumes is prevented by local extraction systems and by enclosures for pre- and post- segmentation operations with directed airflow ventilation and filtering. Exhaust air filter systems are used to prevent the spread of hazardous substances. As part of the dismantling process, regular contamination
prevention and cleaning measures are applied, both within the post-segmentation area and near the reactor cavity. These measures include both the extraction and filtering of fumes and tiny particles by means of smoke extractors and the capture of slag particles close to their formation by means of collection funnels, insofar as this is technologically feasible. In addition, cleaning of the affected areas is carried out after each segmentation campaign. After segmentation, all of the affected areas are cleaned once again to remove contaminants.
Although the dismantling equipment was extensively
tested in a mock-up facility beforehand, improvements were made on site.
Lessons Learned NUKEM Technologies has successfully dismantled and packaged two complete RPVs in the last 24 months. The first rings of a third RPV have been cut out and temporarily stored for further dismantling. The equipment is currently being moved to another site, where the dismantling of two more pressure vessels is planned in the coming months. Even though these reactors are not the same, there is
regular exchange between the different project teams to share findings. Reduction in dismantling times and the associated cost reductions can be achieved through the experience of previous projects. The goal is to save costs and time and to increase the overall quality of work. Within the projects, experience is also exchanged between the construction site and the engineering departments in lessons-learned sessions so that these findings can be incorporated into follow-up projects as early as in the planning and design stage. Furthermore, as the dismantling equipment is used at the site, further modifications and improvements are made. There are always some problems that remain undetected even during the extensive mock-up testing phase. One reason is that it is very hard to achieve identical reproduction of the conditions on site. The equipment also has to be adapted to the structural conditions on site, which often deviate from the design documents that are available. As a result, practical solutions are found which ensure a significantly higher level of safety for the processes and shortened operational times during the dismantling of the following reactor disassembly projects. For example, the dismantling time of the second RPV could be halved to six months, plus assembly and disassembly of equipment. The reduction in the cutting times results in significant cost savings due to the lower personnel costs on the construction site. In addition, the customer benefits on a case-by-case basis from the shorter dismantling time as the reactor room can be released earlier to be used for further activities. ■
www.neimagazine.com | February 2023 | 35
Above left: Removal of a cut piece by means of the lifting beam
Above right: Transport of the RPV calotte to the post- segmentation area
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