Which is an example of an open system?

• A. Condenser Circulating Water System Open to Lake
• B. Reactor Coolant System
• C. Containment Building
• D. Feedwater Heater Shell Side

Answer: (A)

An open system is one in which mass can cross the system boundary. The condenser circulating water system is tied to the lake: cooling water is drawn from the lake into the condenser, circulates through the plant, and is discharged back to the lake (often with some makeup water). That exchange of mass with the surroundings makes it open. In contrast, the reactor coolant system is designed as a closed loop with essentially all its water retained, only minor makeup or venting, not continual mass transfer to the environment. The containment building is a structural enclosure rather than a flow loop, and the feedwater heater shell side operates within a closed feedwater loop with no net mass exchange with the surroundings. So the open-system example is the condenser cooling system open to the lake.