Numerical simulations of the TOPFLOW-PTS steam-water experiment

The correct analysis of the Pressurized Thermal Shock requires the simulation of the thermal mixing that occurs when cold Emergency Core Cooling (ECC) water is injected into the cold leg, where it flows to the downcomer and mixes with the hot coolant present in the primary circuit. In the framework of the NURISP (NUclear Reactor Integrated Simulation Project) project attempts are being made to improve the CFD modeling for two-phase PTS scenarios. For this purpose, two steady-state reference cases from the TOPFLOW-PTS experimental program were defined: one for air-water and one for steam-water flow. The current paper focuses only on the steam-water reference case. The pre-test simulations were performed with the commercial CFD code ANSYS CFX 12.0. The simulations of the steam-water reference test predicted a thermal stratification in the cold leg at the entrance into the downcomer and in the downcomer itself.