In a reactor coolant purification loop, what term describes removing a volume of impure water and replacing it with pure water to reduce impurity fraction?

• A. Letdown/Makeup
• B. Filtration
• C. Ion Exchange
• D. Purification Processes

Answer: (A)

The concept being tested is how impurity levels are controlled in a reactor coolant purification loop through a bleed-and-feed operation. By removing a volume of the loop water that contains dissolved impurities (the letdown) and replacing it with pure water (the makeup), the impurity fraction in the circulating system is diluted and driven lower over time. The letdown stream pumps or transfers a portion of the impure coolant to the purification train, where contaminants are removed or reduced, and then makeup water is added back to the loop to restore volume and maintain proper reactor operations. This continuous cycle of removing a portion of contaminated water and replenishing with purified water is what directly reduces the impurity concentration in the loop, making it the specific term that describes this practice. Filtration, ion exchange, and other purification steps are essential parts of the overall cleanup process, but they describe how impurities are removed from the water; the act of removing a volume and replacing it with clean water to lower impurity levels is the letdown/makeup operation.