Water chemistry in PWR

The primary system of a PWR consists of the primary coolant system, chemical and volume control system, make-up water system, heat removal system and safety injection system. The primary coolant system is pressurized at 157 kg/cm2 and is free from generation of steam. Therefore, the properties of the primary coolant can be controlled in a stable homogeneous state by adding appropriate chemical substances such as boric acid (for control of the core reactivity), lithium hydroxide (for alkalinizing the coolant which is acidified by boric acid) and hydrogen gas (for controlling the generation of oxygen gas due to radiolysis of water). Measures for reducing the 58Co and 60Co concentrations include the control of corrosion, control of radioactivation, prevention of contamination and removal of crud. Inconel of the steam generator heat-transfer pipe is the major source of Ni and Co, parent atoms of 58Co and 60Co. The release of corrosion products from Inconel is decreased at pH above 6.5. Some measures are proposed for water properties control, such as earlier reduction in pH to increase the solubility of crud (earlier addition of boric acid and removal of lithium), extended operation of the primary coolant pump to increase the mass transfer coefficient for dissolved substances, and extended operation of the purification system at the possible maximum flow rate. (Nogami, K.)