Prior to construction, the modular steam generator of the French 250-MW(e) fast breeder demonstration plant (Phenix) was submitted to a number of tests carried out on scale-one module mockups. The Phenix steam generator consists of seven tube coil-shaped modules operated as countercurrent sodium-to-water (or steam) heat exchangers. We report on the experimental verification of the accuracy of the procedures and models utilized to predict the steady-state heat transfer, the pressure losses, and the static stability of a 15-MW(th) mockup comprised of an economizer-evaporator, a superheater, and a reheater tested for 8000 h on the 5-MW(th) CEA facility at Grand Quevilly, and a 45-MW(th) mock-up comprised of three economizer-evaporators, three superheaters, and three reheaters tested 6200 h at Les Renardières on the 45-MW(th) EDF facility.