Transient flow and freezing of molten core debris in coolant channels of the subassemblies of a liquid-metal fast breeder reactor has been an important consideration in postaccident heat removal. As a first step to study this phenomenon, transient freezing of a number of simulant materials in tube flow was investigated experimentally. Controlling parameters of the transient freezing process were determined from theoretical consideration. A parametric study of the effects of the controlling parameters on freezing was carried out, and an empirical correlation based on experimental measurements was obtained that is applicable over a wide range of Prandtl numbers. Results of the present study were compared to the existing analytical models.