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Science and Technology of Nuclear Installations
Volume 2009 (2009), Article ID 436218, 12 pages
Research Article

CFD Analysis of a Slug Mixing Experiment Conducted on a VVER-1000 Model

1Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione, Università di Pisa (UNIPI), 2 Via Diotisalvi, 56100 Pisa, Italy
2Forschungszentrum Dresden-Rossendorf (FZD) Institute of Safety Research, P.O. Box 51 01 19, 01314 Dresden, Germany
3Experimental Thermal Hydraulics Department, OKB Gidropress, Ordshonikidize 21, 142103 Podolsk, Moscow district, Russia

Received 13 June 2008; Accepted 3 November 2008

Academic Editor: Dirk Lucas

Copyright © 2009 F. Moretti et al. 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.


A commercial CFD code was applied, for validation purposes, to the simulation of a slug mixing experiment carried out at OKB “Gidropress” scaled facility in the framework of EC TACIS project R2.02/02: “Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet.” Such experimental model reproduces a VVER-1000 nuclear reactor and is aimed at investigating the in-vessel mixing phenomena. The addressed experiment involves the start-up of one of the four reactor coolant pumps (the other three remaining idle), and the presence of a tracer slug on the starting loop, which is thus transported to the reactor pressure vessel where it mixes with the clear water. Such conditions may occur in a boron dilution scenario, hence the relevance of the addressed phenomena for nuclear reactor safety. Both a pretest and a posttest CFD simulations of the mentioned experiment were performed, which differ in the definition of the boundary conditions (based either on nominal quantities or on measured quantities, resp.). The numerical results are qualitatively and quantitatively analyzed and compared against the measured data in terms of space and time tracer distribution at the core inlet. The improvement of the results due to the optimization of the boundary conditions is evidenced, and a quantification of the simulation accuracy is proposed.