Thermal Hydraulics Laboratory

Air Cooled RCCS Facility

The Reactor Cavity Cooling System (RCCS) is a safety system designed to transfer the core decay heat reliably to the environment under all situations as part of the Next Generation Nuclear Plant (NGNP) gas-cooled thermal reactor design. It is also a crosscutting shutdown heat removal system concept considered for a range of other advanced reactor systems.

The RCCS will be a key safety system designed for the NGNP. The shutdown heat removal system must accommodate limiting accident scenarios and successfully remove core decay heat as well as any long-term chemical reaction heat generated from graphite oxidation in the core via the RCCS.

The air-cooled RCCS operates in a passive mode during accidents, providing heat transport from the reactor cavity to the external atmosphere using natural circulation throughout the accident. During accident conditions when all AC power is lost, natural convection of the RCCS air coolant removes the heat by radiation and/or convection from the reactor vessel wall (RPV) to the RCCS riser ducts facing the RPV. These riser ducts cover the reactor cavity walls and transport the heat to a hot upper plenum then up the chimney to the surroundings, providing long-term core cooling as well as protecting the cavity structure from overheating. Cold air enters the RCCS from an inlet chimney to a common cold plenum connected to downcomer inlet ducts, which connect to the heated risers.

The conceptual design of the air-cooled RCCS risers consist of about 230 rectangular ducts (51mm x 254mm), made of steel. The major heat transfer area of the riser is ~20 m in height and ~40 m to chimney outlets connected by a common outlet plenum (red). Inlet plena (blue) connect to larger downcomer ducts (blue) feeding the risers (purple). The RPV with the surrounding RCCS downcomer and riser array is situated within the reactor cavity, which is below grade in the NGNP design.