During the Steam Generators Replacement Operation at Angra NPP (Brazil), a transfer opening was required in the Concrete Shield Building and in the Steel Containment. For this purpose, structural analyses were conducted using Abaqus in order to verify the adequacy, from a structural point of view, of the works to be undertaken to perform the transfer opening and seal it again. The most appropriate techniques were also assessed and proposed for the cutting and repositioning of the original materials, bar welding and local reinforcements of the transfer opening. Furthermore, the calculation of the loads on the separation walls was conducted after the replacement of the Heat Exchangers.