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Deconstruction of German nuclear power plants

After an extensive testing and approval process, Viega “Megapress” installation components have now also been approved for use in nuclear power plants. Thanks to the fast, safe and cost-effective installation process, operator PreussenElektra is able to make significant savings, both in terms of cost and time, in the decommissioning of its “Unterweser” and “Isar 1” power plants.

There are areas of application in building services engineering that, without doubt, represent the gold standard in installation technology. This may be, for example, due to the fact that their operational conditions or quality requirements far exceed those of conventional areas of application for pipeline systems and their associated installation components. Nuclear power plants such as the “Isar 1” and “Unterweser” plants operated by the energy supplier PreussenElektra are a case in point. Even when the plants are disconnected from the grid, the above-average quality requirements are only minimally affected, irrespective of safety considerations. The closure of pipeline systems (in this case made of thick-walled ferritic or austenitic steel) that were previously used to convey, for example, radioactive water, waste water contaminated with various chemical substances or fully desalinated water – requires almost exactly the same specifications for the remaining and final operational phases prior to the final decommissioning of the pipeline systems (for the requirement levels that remain in place) as for plants still operating at full capacity. This is logical, because decommissioning is carried out in stages and any remaining sections of the extensive pipeline systems continue to function during the process …

Arno Hentschel, a welding engineer with many years of professional experience working for manufacturers, inspectors and now for the operator PreussenElektra, explains why even a relatively simple closing cap has to be a high-end, state-of-the-art product:

“For pipeline installations in German nuclear power plants, there are five defined classes of pipes with proven nuclear specifications. Depending on the pipe class, these specifications stipulate, for example, that each individually welded pipe closure must be ‘uniquely crafted’ and subjected to non-destructive material testing, for instance using radiography, by a qualified and certified testing company. Easing the requirements by reducing the percentage of components subject to non-destructive material testing – as is the case in series production of pipe welds for the construction of nuclear power plants – does not apply here. This makes it a complicated and time-consuming undertaking, because we are talking about a very large number of connection and closure points during the dismantling process.”

 

In addition, many of the pipe closures are located at a height of several metres, just 15 cm below the ceiling, some of which are only accessible using scaffolding. Due to the extreme conditions, only very highly skilled welders would be able to weld here. Furthermore, the welding work requires a disproportionately large amount of time and organisation. The pipelines, made of austenitic steel, would have to be completely filled with large quantities of expensive forming gas prior to welding on account of the risk of oxidation of the weld seam. In many cases, this is virtually impossible because the system has so many branches. In addition, it is vital that the area around the welds is protected against fire transmission. To sum up, welding work is extremely time-consuming and therefore very expensive ... 

With the protective caps from the “Megapress” and “Megapress S” pipeline systems for thick-walled steel pipes and the subsequently developed austenitic steel versions “Megapress Stainless 316”, Dipl.-Ing. Arno Hentschel, together with the system supplier Viega, is now providing an alternative process in the dimensions DN 15 to DN 100, which meets the high quality requirements of PreussenElektra and is cost-effective to install.

Award for Viega manufacturing

A brief look back: A few years ago, following the established press connector systems for copper (“Profipress”) and austenitic steel (“Sanpress” and “Sanpress Inox”), Viega was the first manufacturer to bring the innovative press connecting technology for thick-walled steel pipes in industrial applications to series-production readiness with “Megapress”(see box). This represented a giant leap forward, particularly for the refurbishment or expansion of existing systems. It meant that such installations could now also be carried out during operation or in confined spaces, and above all by any trained HVAC and plumbing fitter instead of a certified welder.

However, there were still major hurdles to overcome before the Viega system caps could be included in the specifications for use in the nuclear power plant installation environment mentioned above. This is because the press connecting technology had not yet been approved for use with neither thick-walled steel nor austenitic steel pipelines. In a multi-stage test procedure, a comprehensive set of requirement specifications had to be drawn up, outlining the special nuclear requirements for the protective caps and their press connection. In close coordination with the VdTÜV inspector and following the release of the requirement specifications, the performance of Viega as a manufacturer was tested and the manufacturing processes involved were approved. After numerous tests had been carried out, a qualification in accordance with VdTÜV allowing the installation components to be used in the respective power plants was put in place, and the Viega protective caps were installed for the first time with EPDM or FKM sealing elements, depending on the medium.

The considerable time and effort invested here is now certainly paying off for PreussenElektra, as “the savings resulting from quicker installation combined with significantly less outlay will be substantial during the course of dismantling all PreussenElektra power plants,” explains Dipl.-Ing. Hentschel. At the same  time, exactly the same level of safety is being maintained while the amount of radiation to which fitters are exposed is significantly reduced.

For Viega as a manufacturer, independent evaluation of its production processes as part of the approval process carried out by PreussenElektra and the VdTÜV provides confirmation of the high-quality “Megapress” production.

Object Deconstruction of German nuclear power plants
Location Germany
Year 2021
Object Type Renovation
Area of use Industry
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