An experimental study on the depressurization of the containment by water spray in a small scale facility

The containment of a nuclear reactor acts as the ultimate barrier for radionuclides to be leaked in the environment. Severe accidents in nuclear reactors may result in the pressurization of the containment and may provide different potential leak paths. So, to enhance the safety of new designs of Indian pressurized heavy water reactors, an additional safety measure called containment Spray System is introduced. The system is designed to cater/mitigate the conditions after design basis accidents. As a contribution to the safety analysis of condition post severe accident, experiments are carried out to investigate the system performance. The accidental conditions are simulated by injecting the saturated steam into the test vessel filled with air at atmospheric pressure and temperature. The effect of different spray parameters such as nozzle geometry, spray mass flow rate and Sauter mean diameter on vessel pressure and temperature is measured. Three initial vessel pressure 1.5 bar, 2.0 bar, 2.5 bar and five different nozzles with nozzle orifice diameter as 1.65 mm, 2.10 mm, 2.45 mm, 2.75 mm and 3.10 mm are chosen for the experimental investigation. The vessel pressures are chosen based on the post accidental conditions in Indian pressurized heavy water reactor. Experiments are conducted with water at room temperature as the spray medium. The experiments are carried out in a vessel of 500 mm diameter and 1200 mm height. These studies are carried out to optimize the containment spray system configuration for best effectiveness. It is seen that the Sauter mean diameter and nozzle geometry influences the depressurization rate of the vessel. The depressurization rate is inversely proportional to the Sauter mean diameter while it increases with the increase in the spray mass flow rate/ Reynolds Number.