Chlorides:

Another parameter which is carefully monitored and controlled within most nuclear facilities is chloride (Cl^-). The purpose for manage the chloride ion concentration at the minimum level practicable is which various forms of corrosion are affected through the chloride ion, and the category of greatest concern is chloride stress corrosion. 

While high levels of Cl^- are suspected, or detected, immediate steps have to be taken to eliminate the source and erase Cl^- from the system since of the potential consequences.  One method of erasing it is to initiate a feed and bleed operation after determining which makeup water supplies is not the source of contamination if Cl^- is present in the reactor coolant system. Because of the huge volume of water generally contained within the reactor coolant system, cleanup through this method includes considerable amounts of pure water and an important amount of time.

Additional problems related along with feed and bleed operations involve changes in pH and a loss of H₂ from the reactor coolant system in during the cleanup.  Modifications to either, or both, of these parameters have the potential to further aggravate the occurrence of chloride stress corrosion since: pH changes from the optimum operating limits cause increased common corrosion; and a loss of H₂ from the reactor coolant makes the dissolved oxygen which is generally present from either contained or radiolysis within the makeup water available to interact along with the Cl^- ions.  That would promote chloride stress corrosion (recalling which Cl^-, O₂ , and tensile stress are all essential for chloride stress corrosion to occur).

Actually that a huge amount of makeup water is being introduced will result within hydrogen depletion since even deaerated water holds small amounts of oxygen.  H₂ will also be lost since of the draining of coolant from the system. In During conditions that require the use of feed and bleed to correct chemistry anomaly of any type, raised attention to all parameters becomes increasingly significant.

Another technique which might be used to control Cl^- concentrations within the reactor coolant is to route more bypass flow by the ion exchanger system, whereas installed.  Use of this system precludes the needs of a huge inventory of makeup water as well as like the disposal problems which arise from the bleed (draining) of coolant from the system.  Since the ion exchanger has minimal effect on dissolved gases, depletion of hydrogen does not contribute to the potential of the problem. Rising flow by the ion exchanger(s) might cause changes to the pH of the system, therefore, and as in the case of feed and bleed, raised vigilance is essential to ensure pH, as well as other parameters, are properly controlled and managed.