Perevezentsev

pp. 40-51

Experimental research of two-phase adiabatic flow in sparging regime in cylindrical vertical channels with different levels of air volume rates was carried out. Vector velocity fields obtained using the optics methods were analyzed to identify a character of the air volumes motion, a bubbles shape, velocities of both phases, a character of the liquid phase motion in the lower part of channel, void fractions. Obtained data describe a structure of two-phase flows in-detail for various flow regimes and can be used as a verification base for math models in modern CFD-codes.

In the experiments the author used a full-scale model of a WWER-440 fuel assembly of the second generation with lead imitators of nuclear fuel tablets. The pilot study technique consisted in free oscillation excitation of a fuel element cluster by sudden removal of concentrated transverse static load which provides the initial sagging of the fuel element cluster. Vibration movements were fixed on the signals of piezoresistive accelerometers which were included in measuring channels with integrating amplifiers. Data on the damping factors indicate the determining role of hydrodynamic processes of dissipation of vibrational energy of a fuel element cluster in comparison with the effects of structural damping.

The article covers a methodology of determining random hydrodynamic loads on the fuel rods beam of WWER fuel assembly by coolant turbulent flow; the methodology is based on measurements of pressure fluctuations distributions on the external perimeter fuel rods beam. Data on random  hydrodynamic loads on a start-up hydrodynamic station and in the area of steady currents for different conditions of input flow pattern formation.  There are two typical areas of influence of random hydrodynamic loads on the intensity of fuel rods beam vibration.