The common foundation slab of the entire nuclear island of Unit 5, which is approximately three meters thick on average, is being built continuously in several bays. Having regard to the huge size of the area and the complexity of the preparation, the area has been divided into several bays in order to carry out the task efficiently and safely. In these bays, the levelling concrete, which includes waterproofing and grounding mesh is first and foremost prepared, in some areas up to one and a half meters thick. The task of the levelling concrete is to provide a solid, clean and even surface for further work. This is followed by the reinforcement, for which massive, 40 mm diameter reinforcing steel bars are used. The volume is clearly demonstrated by the fact that in the 122 square meters area of the first concrete pouring alone, 133 tons of iron structure increase the load-bearing capacity and durability of the foundation slab. The reinforcement bars extending beyond the structure ensure continuity between the completed foundation slab sections.