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Science and Technology of Nuclear Installations
Volume 2010, Article ID 574195, 8 pages
Research Article

Numerical Investigation of Startup Instabilities in Parallel-Channel Natural Circulation Boiling Systems

Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India

Received 11 November 2009; Revised 5 April 2010; Accepted 13 April 2010

Academic Editor: Jose Reyes

Copyright © 2010 S. P. Lakshmanan and Manmohan Pandey. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The behaviour of a parallel-channel natural circulation boiling water reactor under a low-pressure low-power startup condition has been studied numerically (using RELAP5) and compared with its scaled model. The parallel-channel RELAP5 model is an extension of a single-channel model developed and validated with experimental results. Existence of in-phase and out-of-phase flashing instabilities in the parallel-channel systems is investigated through simulations under equal and unequal power boundary conditions in the channels. The effect of flow resistance on Type-I oscillations is explored. For nonidentical condition in the channels, the flow fluctuations in the parallel-channel systems are found to be out-of-phase.