CHELANT PASSIVATION: NEW STUDY CHALLENGES AN OLD MYTH.

Results of DOE-sponsored study and experience support the evidence concerning the ability of chelants to control deposit buildup and limit boiler corrosion. The formation of a protective magnetite film from a solution containing an extremely high concentration of chelating agent was investigated in the course of an investigation of secondary-water chemistry of nuclear pressurized-water reactors (PWRs). The study was related to the impact of chelants on iron oxide accumulation in the crevices of steam generator tubesheets, which leads to tube denting. The basic treatment program used ammonia and hydrazine (all-volatile treatment 0AVT), with ethylenediaminetetra-acetic acid (EDTA) as a chelant. A passivation equation is derived and is tested experimentally by iron addition to the test solution.