The "Enrico Fermi" nuclear power station at Trino Vercellese had an enriched uranium reactor, cooled by pressurised water, with two thermal units for a total of 330,000 KVA. When it first started operation it was the biggest plant in the world. Constructed by Recchi and commissioned by SELNI, a joint venture comprising private and public electricity companies, it had a covered surface area of 13,000 square metres and a total construction volume of 360,000 cubic metres. The foundations of the steel pressure vessel and of the 60-metre high concrete biological protection wall were laid directly on a layer of compact clay marl, 140 metres below ground level to guarantee maximum stability and avoid any risk of environmental contamination.