[en] Three transient thermal-hydraulic models, TRAN I, II, III, have been incorporated into the CORTRAN code. The TRAN I, II, III models are similar in as much as they retain the wire-wrap mixing and swirl flow models of the Energy code, i.e., the wire-wrap mixing is modeled by an enhanced eddy diffusivity in the central regions of the bundle and a swirl flow in the region near the duct wall. The fuel rod and duct wall models required to treat the stored heat and thermal inertia effects, are also similar in the three models. Up to 10 radial nodes are allowed in the rods and 6 radial nodes in the duct wall to solve the one-dimensional conduction equation for the rods and duct wall, by finite difference. Temperature-dependent properties are taken into account in calculating rod temperatures