Experiments were performed with the Three Mile Island reactor coolant system open to the atmosphere and the coolant lowered to a level above the fuel (a condition required for defueling) to ascertain the extent of coolant mixing. A principal concern for coolant decontamination during defueling is the radionuclides released and their distribution within the primary system. Analyses of radionuclide, temperature, and dissolved oxygen data taken during these experiments confirm mixing in the primary system under forced coolant flow conditions with only minimal mixing occurring during static periods.