Results are presented of a study made of the possible extent of zirconium-water reaction and core meltdown following a postulated loss-of-coolant accident in the PWR plant. Zirconium-water chemical reaction and core meltdown occur in the course of the core temperature excursion which could follow a loss- of-coolant if no cooling were provided after an uncovering of the core. An analysis of the temperature excursion involves consideration or the complex relationships between core geometry, decay heating rates, water (or steam) flow through the core, and the thermodynamic and chemical properties of water, steam, and the core materials. Parametric studies of the temperature excursion are used in evaluating the effectiveness of the PWR Safety Injection System in prevention of core chemical reaction and meltdown. Combinations of delay time in operation and rate of injection are considered. (auth)