Experimental Investigation of the Thermal Hydraulic behaviour of Heavy Liquid Metal Cooled Reactors

This work reports on an activity performed at the Brasimone ENEA research centre, concerning the heavy liquid metal technology, component development and demonstration facility design. The Brasimone research centre is strongly involved in the most important international R&D activities on energy and environment and has wide competencies and capabilities in the frame of the nuclear fission energy. It is also involved in the main European research programmes, as IP-EUROTRANS, ELSY, and VELLA, devoted to the development of pool-type nuclear reactors cooled by heavy liquid metal. Starting from 2003, the University of Pisa, and in particular the Department of Mechanical, Nuclear and Production Engineering, collaborates with ENEA, supporting the activities by numerical simulations, procedure qualification, experiment definition and experimental facility design. The present doctoral work is performed in the frame of this collaboration. The gas-injection enhanced circulation phenomena in a HLM pool were characterized; the reliability of this technique as suitable pumping system for HLM pool type system was proven by the experimental tests performed on the CIRCE facility. Then, the design of the ICE experimental activity, to be performed in the CIRCE facility is reported. Considerable efforts were spent in the design of the heat source, of the heat exchanger and the test section; the obtained results are here reported together with the supporting numerical simulations performed by a system code and a CFD code. ICE represents the main experiment of the Integral Test envisaged in the DEMETRA domain of EUROTRANS and, when completed, it will strongly contribute to the design and construction of a HLM pool-type nuclear reactor. Finally, the design of the NACIE loop is described; this facility consists in a simple HLM loop, designed and built by the Brasimone Research Centre, with the aim to support the ICE design by running experimental tests in the field of natural and gas enhanced circulation. The NACIE loop and the CIRCE facility will strongly contribute to the experimental analysis of the thermal-hydraulic behaviour of HLM prototypical systems and test procedures, covering the existing knowledge gaps in some fields as, for example, heat transfer in fuel bundles in HLM under the natural circulation flow regime