Experimental Measurement and Analysis of Natural Circulation Flow Oscillations in a Vertically Heated Channel
Fuel utilization and passive safety are some of the important design aspects of advanced reactors. Thorium due to its abundance and importance in providing sustainable energy has been considered as future fuel for advanced reactors in India such as advanced heavy water reactor (AHWR) and compact high-temperature reactor. AHWR uses thorium-based fuel and has passive natural circulation of water in parallel channels in its primary heat transport and decay heat transport systems. The two-phase boiling heat transport system exhibits oscillations and flow instabilities in varying scales in operating and accident conditions and they influence the thermal and reactivity margins in design. Experimental studies on natural circulation at low pressures assume importance in understanding the heat transport mechanisms and system behavior in case of a loss of coolant accident or a pressure boundary failure. The present research work highlights the multimodal oscillations, measured in a boiling natural circulation loop and experimental studies on the physics behind the components contributing to the flow oscillations. The boiling parallel channels of the facility are vertical with central heater simulating a typical vertical coolant channel with fuel in a nuclear reactor. The bubbles and slugs in the flow channel have been observed to form and coalesce around the length of the heater and flashing has been observed at a higher elevation. The sequence of events has been nearly similar, but appeared faster at increased heating rates. The overlapping temporal and spatial events in the channel lead to new nonlinearities and multimodal chaotic oscillations. Advanced signal analysis methods have been applied to the signals to study the time-evolving characteristics of flow oscillations at different channel heating rates.
KeywordsNatural circulation Multimodal oscillations Empirical mode decomposition Fast Fourier transform
The authors thank Dr. P. K. Vijayan and Shri I. V. Dulera, for their valuable support in carrying out the experimental work. The authors also acknowledge with thanks the support extended by the operations and maintenance personnel of the Reactor Engineering Division for conducting the experiments.
- 2.A. Manera, Experimental and analytical investigations on flashing-induced instabilities in natural circulation two-phase systems-applications to the startup of boiling water reactors. Research thesis, 2003, ISBN: 90-73861-44-6Google Scholar
- 3.J. Aparna, B.V.S.G. Sharma, Design & development of experimental measurement and analysis methods for the natural circulation flow distribution studies in transparent parallel channels, in Proceedings of NCFMFP 2006-33rd National and 3rd International Conference on Fluid Mechanics and Fluid Power, 2006Google Scholar
- 4.J. Aparna, A.K. Nayak, I.V. Dulera, P.K. Vijayan, Experimental measurement and interpretation of natural circulation two-phase flow signals in a vertically heated channel during flashing induced oscillations, in New Horizons in Nuclear Reactor Thermal Hydraulics and Safety, Mumbai, India, 13–15 Jan 2014Google Scholar
- 7.A. Libchaber, J. Maurer, A Rayleigh Benard experiment: helium in a small box, in Nonlinear Phenomena at Phase Transitions and Instabilities (1983), pp. 259–286Google Scholar