Covra NV (Centrale organisatie voor radioactief afval) is a Dutch company that stores radioactive waste temporarily, including low-level radioactive waste from hospitals. Because the present storage building would become inadequate in the foreseeable future, the decision was made to build a second. The NOEtop wall formwork system was selected for this task. The formwork and falsework for this construction project was supplied by Arkel-based NOE-Bekistingtechniek B. V., the Dutch subsidiary of NOE-Schaltechnik.
The new building, known as VOG2, will provide temporary storage for the low-level radioactive waste created in the Netherlands for the next 15 years. It consists of three long storage lines. In one of these lines, the waste is received, presorted and taken to its storage location by an overhead crane. The building’s floor slab is supported by 1,800 piles driven into the ground. The building itself has a plan area of approximately 80 x 93 metres and walls 13.25 metres high. The external walls are 75 cm thick and consist of a 40 cm thick inner leaf, 15 cm thick insulation layer and 20 cm thick external fair-faced concrete outer leaf.
75 cm thick in-situ concrete wall
All the walls were constructed in in-situ concrete, for which the site team decided to use NOEtop wall formwork. This system excels through its ease of handling, great flexibility of use and outstanding robustness. For example, the frame and profiles are hot dip galvanised inside and out. All formwork panels have cast corners and their profiles have a uniform thickness. In addition to standard-sized panels, the company can also supply NOEtop XXL panels, which also have integral bracing members. The largest of these panels has dimensions of 5.30 x 2.65 m and allows users to cast an area of more than 14 m² quickly and efficiently without a single butt joint. The various sizes of panels can be combined end-on or side-on in the NOEtop panel system, without disrupting the consistency of the panel pattern. This advantage was made good use of on the site in Borssele. It enabled the NOEtop panels to be combined in such a way that a special detail of the building was integrated very smoothly into the construction process: the construction of corbel supports in in-situ concrete.
Two different corbel supports in one pour
In the construction of the storage facility, the site team had to cast two different types of corbel: one for the overhead crane and another for the installation of the roof. The waste containers are transported within the storage facility by an overhead crane. The crane is installed on separate, individual corbel supports at a height of 7.30 m. The roof of the building consists of prefabricated concrete units. These are placed on continuous corbel supports that form the top of the walls. In order to cast the corbels and the walls in one pour, the site team built a formwork mould of the required dimensions using NOE Combi 20 girders and braced the construction with NOEtop panels. The walls and corbels were cast together as a unit. The storage facility walls were cast in 25 separate sections.
Although NOEtop can withstand a concrete pressure of 88 kN/m², the concreting team had to proceed very carefully on site. The area that had to be concreted in one pour was so large it took between eight and nine hours to complete in some cases. Another requirement was that the outer leaf of the wall had to be formed in fair-faced concrete and therefore fulfil higher aesthetic requirements.