How is reactor coolant chemistry managed and why?

Reactor coolant chemistry is carefully managed to prevent corrosion, minimize the buildup of radioactive contaminants, and ensure the safe and efficient operation of the reactor. The coolant, typically water, is in direct contact with the reactor core and other components, making it susceptible to corrosion and the transport of radioactive materials. In Pressurized Water Reactors (PWRs), the coolant chemistry is typically managed by adding lithium hydroxide (LiOH) to control the pH and hydrogen to suppress the formation of oxidizing radicals. Maintaining a slightly alkaline pH helps to minimize corrosion of the reactor materials. The hydrogen also scavenges oxygen and other oxidizing agents, further reducing corrosion. Boric acid is added to the coolant to control reactivity. The concentration of boric acid is adjusted to compensate for fuel burnup and maintain a constant power level. In Boiling Water Reactors (BWRs), the coolant chemistry is managed by controlling the oxygen concentration and the pH. Oxygen is produced by the radiolytic decomposition of water in the reactor core. High oxygen concentrations can lead to increased corrosion. The pH is controlled by adding small amounts of volatile amines. Continuous monitoring of the coolant chemistry is essential to ensure that it is within the specified limits. Samples of the coolant are regularly analyzed for pH, conductivity, dissolved oxygen, and the concentration of various chemical species. If the coolant chemistry is not within the specified limits, corrective actions are taken to restore it to the proper conditions. Proper management of reactor coolant chemistry is crucial for preventing damage to the reactor core and other components, reducing the radiation exposure to plant personnel, and ensuring the long-term reliability of the plant.