Magnetite Deposition Behavior on Alloy 600 and Alloy 690 Tubes in Simulated PWR Secondary Water

Fouling due to magnetite deposition has been a major concern for steam generator (SG) tubing of pressurized water reactors (PWRs). Alloy 690 SG tubes are now used for new plants or are scheduled to replace old Alloy 600 tubes of operating plants. The purpose of this study is to investigate the magnetite deposition behavior on the two different SG tube materials: Alloy 600 and Alloy 690. Deposition tests were conducted under a sub-cooled nucleate flow boiling condition in simulated secondary water of a PWR at 270 degrees C. After these tests, we observed that the tube surfaces were covered with deposits composed of porous magnetite particles. We found approximately 30% more magnetite deposits on Alloy 600 than on Alloy 690. The electrostatic repulsive force between the magnetite particles and the Alloy 600 surface was only half of that between the magnetite particles and the Alloy 690 surface, resulting in an increase in the deposit mass.