The refill phenomena occurring from 200 to 217 min of the Three Mile Island Unit 2 accident were analyzed by using measurement data including the reactor coolant system (RCS) pressure and the pressurizer level. At 200 min, the high-pressure injection (HPI) system began to inject water into the RCS, resulting in a primary system depressurization due to steam condensation; and the pressurizer water drained into the reactor vessel, increasing the liquid level at the core. It is believed that the core was completely covered by water by ∼207 min, when the pressurizer level decrease and the RCS depressurization stopped. Continued HPI resulted in increasing hot-leg water levels; and the pressurizer level began to increase at ∼210 min, when water reached the level of the surgeline entrance to the hot leg. Analysis of the refill assuming uniform liquid levels in the RCS fails to predict the observed phenomena. A set of equations describing the refill phenomena and accounting for compression of noncondensable gases has been derived from theoretical considerations, and solutions for water levels throughout the RCS have been obtained to correctly predict the phenomena occurring during the refill period.