[en] Trepaud's steam generator (G.V.T.) for light-water, heavy water and sodium-cooled reactors constists of a vertical unit, operating with once through counter-current flow. It uses undulating tubes and produces superheated steam. There are two types of steam generators for PWR reactors on the market at the moment: those with U tubes which reduce tube dilatation effects, but do not offer the advantages of a counter-current flow. They produce wet steam (with 0.5 to 1 pc humidity); those with straight tubes which offer a once-through counter-current flow they produce a superheated steam, but with the stresses arising from dilatation. G.V.T. combines the advantages of both, without suffering their disadvantages