Since all materials of construction are not compatible with spray solutions, an additional problem must be resolved. The corrosion of aluminum and zinc fabricated or coated components in a typical PWR plant when contacted with the sodium hydroxide in the alkaline sodium thiosulfate spray solution is a major contributor to post-accident hydrogen generation. When the hydrogen from metals corrosion is combined with the hydrogen generated from radiolytic decomposition of the coolant and the Zircaloy-water reaction of the overheated fuel cladding, hydrogen can reach a flammable concentration level in the reactor building within 1 to 2 months after a LOCA.