Experimental study on void fraction in tight-lattice rod bundles

Japan Atomic Energy Research Institute (JAERI) is carrying a design study on the Reduced- Moderation Water Reactor (RMWR). The RMWR adopts a triangular tight-lattice fuel rod configuration with a gap of about 1mm between rods, and is based on the BWR technology. Void fraction database in such a tight bundle is indispensable to verify the numerical analysis codes for the design study. Void fraction experiments were conducted in order to make clear the void fraction characteristics and to develop the prediction method for tight-lattice rod bundles. Void fraction in bundles was measured by Neutron Radiography (NR) and quick-response area-averaged void fraction meter. These measurement systems have been newly developed by the JAERI. Experiments were performed using two test sections under atmospheric pressure conditions. Void fraction of air/water two-phase flow and boiling flow was measured by above mentioned two methods. Measured range of the void fraction is 0.07 - 0.92. Time-averaged void fraction was evaluated with the quality or the superficial momentum fluxes of liquid and gas phases as a parameter. Fluctuation of the void fraction is about +/- 0.1 in case of RMWR simulation condition (void fraction is about 0.8). Void fraction maps were made by the present database in order to verify the numerical analysis codes. Void fraction was correlated well by the drift-flux model. Distribution parameter and drift velocity are evaluated using the present data