The Reactor Cavity Cooling System (RCCS) is an important passive cooling safety system used to cool the cavity of generation IV Very High Temperature Reactors (VHTR). Texas A&M University built a 1/8 scale experimental facility for the air-cooled Reactor Cavity Cooling System (RCCS) based on General Electric Modular High Temperature Gas Cooled Reactor (MHTGR) design to study the thermal hydraulic phenomena occurring in the upper plenum. The facility consists of four vertical parallel riser ducts welded to the upper plenum which has two exhaust chimneys. Blowers are used to drive air through in-line heaters which are connected to the bottom end of the riser ducts. Experiments were conducted to measure the temperature spatial profile in the plenum. Type T thermocouples were mounted on six moveable racks inside the upper plenum, which were moved during the experiments to measure the temperature profile across 6 different planes. Measurements were taken for four different cases with different boundary conditions. Two cases operated with heated air flow in all four risers, whereas the other two were performed with flow in a single riser only. The obtained temperature profiles were asymmetric and suggested the presence of reverse flow from one of the chimneys in both single riser cases and in one of the four riser cases. The other four riser case exhibited a symmetric temperature spatial profile indicating even distribution of the flow across the exhaust chimneys.
