Westinghouse pressurized water reactors have experienced soluble releases of 58Co and natural 58Ni into the reactor coolant during refueling shutdowns. When the soluble inventory of 58Co was not managed properly, the refueling water became contaminated, forcing delays in refueling operation schedules. Subsequent testing at other refueling shutdowns identified the development of oxygen species in the coolant as the prime reactant causing the dissolution. Hydrogen peroxide addition to reactor coolant under prescribed conditions was successfully used to create a controllable and soluble release of 58Co and nickel. The controlled release permitted a more deliberate removal of the activity by ion-exchange purification. A lesser, soluble release of the activity was shown to be caused by the depression in reactor coolant pH resulting from dissociation of boric acid following reactor coolant system boration and cooldown.