Optimized Monitoring of Ammonia Water Chemistry in the Primary Coolant Circuit of Small Capacity Light Water Reactors

The article presents the results obtained from a study of the processes occurring in the primary circuit coolant of a KLT-40S propulsion light water reactor in conducting the ammonia water chemistry (WC) in it. At the fuel residence cycle initial stage, a high concentration of acetate ions (200‒220 ppb) was noted in the coolant, and their content turned to be prevailing among other anion impurities. In the course of reactor operation, their concentration in the coolant decreased as a consequence of radiolysis and thermal oxidation processes. Other anions, including those that cause local corrosion of structural materials (chloride and sulfate ions) were present in the coolant of both the operating and shutdown reactor in low quantities: not more than 15 ppb. The results obtained from the study of the behavior of anion impurities in the primary circuit coolant point to the possibility of long-term operation of the nuclear power facility (NPF) without the need to connect ion exchange purification filters, the operation of which in normal operation modes can cause contamination of process media with the products of their own destruction. Proceeding from the experience gained from operation of propulsion light water reactors, ways for improving the primary coolant circuit water chemistry (WC) for small capacity nuclear power plants (SNPPs) are proposed; in particular, it is recommended to maintain the standardized concentrations of reference anions in the coolant of the shutdown reactor and also to maintain the coolant parameters at the diagnostic level in the course of cooling down the reactor. It is proposed to adopt, as the standardized indicators of the SNPP primary circuit coolant, the concentrations of chloride and sulfate ions for the shutdown reactor equal to 50 ppb and adopt, as diagnostic indicators in cooling down the reactor, the concentrations of chloride and sulfate ions equal to 100 and 200 ppb, respectively.