Concrete base slab1

The parties to the contract were the plant builder (Areva ANP, AREVA), the structural designer of the base slab (Finnprima), the concrete supplier (Forssan Betoni Oy) and the contractor that performed the concreting work (Hartela Oy).

The reactor building, the safeguard buildings and the fuel building share a common base slab. the design bases of the slab include loads during the construction stage, loads during plant operation, loads caused by internal accidents or external collisions against the plant, as well as earthquakes. Security against collapsing of the entire construction based on the slab as a result of earthquake or collision loads has also been required.

The base slab is 103.1 m wide and 100.8 m long. The thickness of the slab under the reactor building is 3.15 m and under the safeguard buildings 1.5 m. The slab is over its entire area supported on rock. The concrete composition used in the base slab is not used in conventional construction work, and in that sense it is rare. Similar mixes are mainly used only in massive structures. The type of concrete used in the base slab cannot be considered to pose any special difficulties in fabrication or concreting, provided the concrete mix has been validated with sufficient preliminary tests.

The consortium AREVA-Siemens (CFS) selected Forssan Betoni from the four potential concrete suppliers apparently on price grounds, although the small size of the company was considered a risk. However, Forssan Betoni had taken part in some large-scale construction projects before, such as bridges and power plants, and according to CFS the company fulfilled the criteria defined for the selection.

At the time the agreement was concluded, Forssan Betoni was not required to have a valid certified ISO 9001 quality system, although most of the other candidates were already at the time using an ISO 9000-based quality system.

Hartela Oy was chosen by AREVA as the concreting contractor from among several candidates. The selection was strongly influenced by TVO's request to employ Finnish contractors on the site.

According to information received from TVO, the large base slab concreting operation on 3 October was started using the designed and approved composition of concrete. TVO's supervisors detected problems in the concreting work on the afternoon of the first concreting day.

After months of investigations, Areva decided to replace Hartela Oy? with giant French construction giant Bouygues Trravaux Publics.

1 STUK Investigation report 1/06