Title: Investigation of flashing-induced instabilities at CIRCUS test facility with the code ATHLET

Authors: Frank Schafer, Annalisa Manera

Addresses: Forschungzentrum Rossendorf e.V., Institute of Safety Research, P.O. Box 510119, D-01314 Dresden, Germany. ' Forschungzentrum Rossendorf e.V., Institute of Safety Research, P.O. Box 510119, D-01314 Dresden, Germany

Abstract: The test facility CIRCUS (CIRculation Under Start-up) was built to study the start-up phase of a natural-circulation BWR. During the start-up,so-called flashing-induced instabilities can arise. These instabilities are induced by flashing (i.e., steam production in adiabatic conditions) of the coolant in the long riser section, which is placed above the core to enhance the flow rate. The flashing that occurs in the riser causes an imbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations. Within the European-Union 5th Framework Programme, a project, NACUSP (Natural circulation and stability performance of BWRs), has been started in December 2000, having as one of its main aims the understanding of the physics of the phenomena involved during the start-up phase of natural-circulation-cooled BWRs, providing a large experimental database and validating state-of-the-art thermo-hydraulic codes in the low-pressure, low-power operational region of these reactors. One part of this project deals with the modelling of selected CIRCUS tests using the thermo-hydraulic code ATHLET (Analysis of THermal-hydraulics of LEaks and Transients). This paper gives an overview about experiments and simulations. The code ATHLET is used to investigate the dynamic behaviour of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

Keywords: natural circulation; flashing; flow instabilities; boiling water reactors; BWR; ATHLET; nuclear reactors; nuclear energy; nuclear power; nuclear technology; nuclear science; thermo-hydraulic codes; modelling; simulation.

DOI: 10.1504/IJNEST.2006.010715

International Journal of Nuclear Energy Science and Technology, 2006 Vol.2 No.3, pp.209 - 218

Published online: 20 Aug 2006 *

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