Preliminary numerical studies of an experimental facility for heat removal in natural circulation

In the recent years particular attention has been dedicated to the study of passive safety systems for the heat removal in nuclear power plants. The reason resides in the degree of safety they can achieve, as they carry out their mission relying solely on physical principles like natural circulation, without any need for operator response or source of energy. For a correct qualification of these systems experimental activities are necessary to study and comprehend the physical phenomena involved, also because they may be equipped with innovative heat exchangers that have to be qualified for the operation. The following paper shows the design activities of an experimental facility to be installed in the laboratories of the Energy Department of Politecnico di Torino. The facility is inspired by the decay heat removal system for ALFRED fast reactor and comprehend a one meter heated bayonet tube and an heat sink for the heat removal constituted by an heat exchanger inside a water pool. The overall thermal power involved is in the order of 1 kW. A RELAP5-3D model of the facility concept has been developed and sensitivity analyses were performed to highlight the effect of the type of heating system, the dimension of the final heat sink, the mass of water stored inside the loop and the geometry of the heat exchangers. The results of this preliminary phase will be used to understand the physical limits of the facility, to demonstrate a preliminary feasibility and to optimize the geometrical parameters for the desired operating conditions.