EPRI Core Protection NANTeL Practice Test

Subcooling is the difference between the coolant’s actual temperature and its saturation (boiling) temperature at the loop pressure. Keeping the RCS loops sufficiently subcooled prevents boiling during normal operation and transients, ensuring single‑phase flow, stable pump performance, and effective heat transfer. The minimum subcooling value used in design is 30°F, which provides enough margin against local flashing as heat input and pressure variations occur. Subcooling less than this risks the onset of boiling; a higher value like 40°F would still be safe but is not the minimum.