Experimental study of the two-phase natural circulation using visualization and ultrasonic techniques

Abstract

This work presents an experimental study on natural circulation performed in the Natural Circulation Circuit (CCN) installed at the Experimental Thermo-Hydraulics Laboratory (LTE) of the Nuclear Engineering Institute (IEN/CNEN). The CCN was designed based on the concepts of reduced scale and similarity. The behavior of the circuit is similar to a Passive Residual Heat Removal System of Advanced Pressurized Water Reactors (APWR). The circuit is composed of heater, heat exchanger and expansion tank that are interconnected by pipes representing hot and cold legs. One part of the hot leg is a boron-silicate glass tube where the flow can be visualized. The heater generates electric power similar to thermal power in the core, resulting from the decay of nuclear reactions, assuming the reactor is operating in sub-critical state. The heat transfer between primary and secondary fluid occurs in the heat exchanger. The expansion tank is installed on the cold leg. Data of flow and temperature are obtained by an data acquisition system. An ultrasonic technique was employed comprising a pulse-technique for bubble velocity and size measurements, and Doppler technique for liquid flow and velocity measurements. An image acquisition system formed by a high-speed camera, software for image acquisition , personal computer and Ethernet network allowed to identify the flow patterns.