Steam Generators

Two model Delta-75 steam generators are used in the AP600. The Delta-75 steam generator is based on standard Westinghouse Model-F technology. The Model-F is a proven design with approximately 75 units currently in commercial operation. The Model F-type replacement steam generators have an impressive record of less than one tube plugged per steam generator for every four years of operation. This is the highest level of reliability achieved by any steam generator worldwide.

Steam Generator Reliability

These reliability achievements are due to a variety of design enhancements incorporated to improve performance and increase service life. Enhancements include full-depth hydraulic expansion, stainless steel broached tube support plates, the use of thermally-treated Inconel 690 (I-690) for the tube material to improve corrosion resistance, the addition of upgraded anti-vibration bars to reduce wear, upgraded primary and secondary moisture separators, and use of a triangular tube pitch.

Steam Generator Materials

Westinghouse led in the development of the I-690 tube material which has been endorsed by the Electric Power Research Institute (EPRI) for use in new steam generators. I-690 has excellent overall corrosion resistance, is resistant to primary water stress corrosion cracking, and has low primary release rates which are expected to reduce primary side radiation levels by at least 50 percent compared to units employing I-600 tube material.

The Delta-75 steam generator used for the AP600 is currently in use at the V.C. Summer plant in the U.S., and has completed one 18-month cycle of operation with the new steam generators. The design enhancements incorporated into the Delta-75 steam generators have provided the plant greater operating flexibility and increased safety margins.

Steam Generators