Measurements of natural circulation flow in a scale model PWR reactor system during postulated degraded core accidents using laser anemometry

The natural circulation of a single-phase fluid in a scale-model pressurized water reactor system was studied during a postulated degraded core accident. A half section of a one-seventh scale model with a plexiglass adiabatic window was employed. Water and SF6 were used as the fluid. LDA was used to perform velocity measurements along the center plane of the model at five elevations. It was found that the recirculation flow patterns are nearly symmetric except near the hot legs and in the upper head and that the fluid in the upper plenum is well mixed.