Gravity driven flows may induce oscillations influencing the stability of natural circulation nuclear boiling water reactors. To experimentally study such phenomenon, a facility based on fluid-to-fluid downscaling modeling is proposed. New design criteria are developed for that purpose. It is found that a unique geometrical scale has to be used for all radial and axial dimensions. Moreover, the geometry and the time scaling are not independent each other. A Freon-based downscaled version of the economical simplified boiling water reactor (ESBWR) is designed and constructed based on the derived scaling rules. Experimental results show good agreement with numerical simulations regarding the static behavior and also the stability performance. (C) 2007 Elsevier Ltd. All rights reserved.