In many pressurized water reactors, containment spray is used to remove fission products, particularly iodine, from the containment atmosphere following a loss-of-coolant accident (LOCA). Elemental iodine is absorbed into the spray drops as they fall through the containment. To achieve permanent removal of the iodine from the containment atmosphere, the spray solution contains ∼0.2M boric acid and ∼0.15M NaOH. This paper describes the spray additive system’s design and criteria used in large nuclear power plants to ensure that the containment spray solution can perform its iodine removal function.