General Corrosion Summary (Cont.)

Corrosion DOE-HDBK-1015/1-93 GENERAL CORROSION Rev. 0 CH-02 Page 21 General Corrosion Summary (Cont.) During the initial fill of a reactor system, great care is taken to promote the formation of the best possible protective corrosion film. The protective film acts as a barrier and stops further uncontrolled corrosion from taking place. This process, called pretreatment or pickling, involves careful control of reactor coolant water chemistry and temperature during the pretreatment period. Four methods used to chemically control general plant corrosion are: Passivators (inhibitors) consist of a naturally active metal that corrodes at a very low rate. A common passivator is potassium chromate. Cathodic protection is the external application of an external electric current to the iron so that it acts as a cathode and has no anodic areas. This is accomplished by using either an external electrical source or the use of a sacrificial anode to provide the electrical current. Removing corrodants to reduce the dissolved oxygen and lesser extent carbon dioxide. Treating the water in this manner reduces the dissolved solids and reduces the conductivity. Chemical addition to alter the chemical reaction or tie up a particular corrodant. Filming amines, phosphates, and sodium hydroxide are used to provide organic films and adjust the system pH. The six water chemistry conditions that limit corrosion of aluminum are: Maintaining pH slightly acidic with the value of the pH depending largely on operating temperature. Elimination of dissolved oxygen Elimination of soluble and solid impurities Prevention of the introduction of organic impurities Pretreatment (or pickling) Maintaining water purity