Abstract: The present invention includes an apparatus for watertight sealing of a steam generator nozzle and methods for installing the apparatus. The apparatus comprises a nozzle dam, a nozzle dam attachment ring, and a seal. The attachment ring is provided in an interior of the nozzle and has a plurality of retaining tabs and a nozzle dam landing. The nozzle dam is adapted for insertion into the attachment ring and abutment against the nozzle dam landing. The nozzle dam has a plurality of radial protrusions adapted to interlock with the retaining tabs for fixing the nozzle dam in the attachment ring upon rotation of the nozzle dam in the attachment ring. The seal covers at least one side of the nozzle dam for effecting a seal between the nozzle dam and the attachment ring. The present invention also provides methods and apparatus for the pressurization and control of nozzle dam seals.