Tests to guarantee safety in the Paks II project

Safety awareness in the nuclear industry is as much a feature of construction as it is of operation. In this spirit, two new units are being built at Paks, north of the existing four. A practice of testing before any major activity is already being carried out during site preparation work. This was also the case for the site preparation slurry wall and the soil stabilisation activities: a 32-metre test slurry wall was built before the construction of the 2,700-metre long slurry wall to ensure water tightness, and a test soil stabilisation was carried out on the site to assess the feasibility of the planned solution - deep soil mixing. The results of the tests were also examined by the National Nuclear Energy Office and were used as a basis for the granting of the construction permits.

A further indication of the safety consciousness of the project is the fact that when the Block 5 zone melt trap was built, two additional valves were built in addition to the eight melt valves that came with the equipment to demonstrate that the valves would start to melt at the required temperature if necessary. But there is also the production of the reactor vessel, the heart of the nuclear power plant, whose components are being made into test pieces identical to the final one, which will be shipped to Paks several months before the vessel arrives, so that the procedures and steps to be taken during installation, such as welding, can be tested on site in good time.

For a similar purpose, the process used for concreting the base slabs of the new blocks was recently studied on a model of the same size as the original. The experts carried out a mock-up test, i.e. a 1:1 construction of a section of the reactor building's baseplate with a footprint of about 4×8 metres and a thickness of 3 metres. The aim of the procedure, which was carried out in the presence of experts from the National Atomic Energy Authority, was to model the construction, particularly in view of the mass concrete nature of the thick structures. The experts studied the behaviour of the material, the technical parameters of the concrete, its spatial distribution, homogeneity and stability, and the filling of the spaces. The hardening of concrete is an exothermic process, i.e. it generates heat, so they also monitored whether the concrete temperature would reach the critical 70 °C, i.e. whether temperature-reducing admixtures would be necessary. The volume of work involved is illustrated by the fact that 6 cubic metres of sub-base concrete, 90 cubic metres of concrete, 26 tonnes of reinforcing steel and half a tonne of tie wire were used to construct the model of the base plate. A smaller 3×3 m pre-mock-up concrete block was also made beforehand to detect any defects and deficiencies - in other words, in this case, a test preceded the test.

The successful mock-up test is just one of the eight hundred or so steps that are invariably a prerequisite for the production of the 5th block of the base plate. This, i.e. the pouring of the first concrete, is a symbolic step because the International Atomic Energy Agency classifies the nuclear installation as under construction from this moment, i.e. the start of the pouring of the core of the nuclear island. Work is scheduled to start with the completion of the baseplate under the control building of the Block 5 nuclear island.

It is interesting that the six buildings of the nuclear island are built on a common base plate. The scale of the task is illustrated by the fact that a total of 88 thousand cubic metres of precast concrete and 60 thousand cubic metres of structural concrete will be needed for the base slabs of the two blocks, and some 19 thousand tonnes of reinforcing steel. To sum up, a total of 63 thousand cubic metres of concrete and 7000 tonnes of reinforcing steel were used for the complete construction of MOL Campus - so the construction below ground level alone will significantly exceed the total construction raw material requirements for MOL.