Transient cooldown in a model cold leg and downcomer. [PWR]

This report describes an experimental program of fluid mixing experiments performed at atmospheric pressure in a 1/5-scale, transparent model of a cold leg, downcomer, lower plenum, pump simulator and loop seal typical of Westinghouse and Combustion Engineering Pressurized Water Reactor (PWRs). The tests were transient cooldown tests in that they simulated an extreme condition of Small Break Loss of Coolant Accident (SBLOCA) during which cold High Pressure Injection (HPI) fluid is injected into stagnant, hot, primary fluid with complete loss of natural circulation in the loop. Cooldown in this new test series is much slower than in previous tests that did not model the pump simulator and loop seal volumes. For the stagnant loop condition, the dominant buoyancy force diverts cool HPI water to the additional volumes.