Reactor pressure analysis at the initial stage ofa loss of coolant accident

To analyze the initial non-equilibrium stage of a loss of coolant accident (LOCA), a simple model of vessel blowdown has been developed. The model consists of a pressurized vessel and a discharge pipe, which connects the vessel bottom to ambient conditions. Initially, both vessel and pipe are filled with saturated liquid and its vapor. The discharge starts when the pipe end is suddenly opened. The system is described by the equations of the vapor volume behavior, the liquid level in the vessel, the vapor production in the liquid and the discharge rate of the liquid through the break. The study of such equations explains the earliest depressurization states and their influence in the mass flux through the pipe. The model is finally validated comparing theoretical results with some Marviken experimental data.