Temperature Fluctuations in a CANDU Moderator Test Facility

A two-dimensional numerical model of the CANDU Moderator Test Facility (MTF) is presented. The results show fluctuations in velocity and temperature. The thermal solution of the MTF model indicates that the buoyancy forces dominate in the inner core of the tank, whereas, the inlet jet induced inertial forces dominate the outer edges of the tank. The interaction between these flows forms a complex and unstable flow structure within the tank. The largest flow fluctuations occur outside the tube bank where the inlet jets continue to flow, and around the top of the tank where the two inlet jets impinge on each other. The high velocity gradients between the inlet jets and the surrounding slower moving moderator fluid generate small vortices with low fluctuation amplitude but high frequencies.