Thermal stratification may be responsible for the development of severe cracks in the feedwater line of steam generators in pressurized water reactors, leading Framatome to carry out an experimental program especially dedicated to this problem. This developmental program analyzes the mechanisms and the driving parameters of thermal stratification. It develops and qualifies an antistratification device to prevent thermal stratification at the steam generator feedwater nozzle location. The program also compares on-site measurements with mockup results. The outcome of the experimental program is a qualified helical antistratification device to be installed in the thermal sleeve of the steam generator feedwater nozzle. As required, this device significantly reduces thermal stratification effects in the feedwater system, even in very low feedwater flow conditions.