Experience Gained with Chemically Cleaning the Evaporators of the Beloyarsk NPP BN-600 Reactor Plant Sodium–Water Steam Generators from Deposits

Abstract—

In the course of steam generator operation, deposits accumulate on the surfaces of their structural materials, whatever the steam generator type. These deposits consist of corrosion products, various nonvolatile salts and bases, organic impurities, and other compounds. Iron oxides impregnated with water-soluble salt impurities form the base of the chemical composition of these deposits. This medium is corrosive in nature and can eventually give rise to local corrosion of structural material. This process results in that the coolant flowrates decrease, heat transfer becomes less intense, local corrosion occurs under the deposits, and, as a consequence, a steam generator leak occurs. Such problems are solved in the main by cleaning the steam generator with a cleaning solution containing chemically active components. In view of great experience gained with implementing similar measures in various industry sectors, it is especially worth noting the technology of carrying out operational chemical cleanings (OCC) of sodium–water type steam generators, which have a number of specific features both during their normal operation and in carrying out OCCs aimed at preventing loss of their circuit-to-circuit tightness. In view of this, the OCC conducting technology needs the process to be continuously monitored. For the time that the BN-600 reactor plant (RP) had been in operation, the steam generator evaporators were regularly subjected to operational chemical cleanings. Chemical cleanings are carried out with sodium circulating in the secondary circuit for continuously monitoring the circuit-to-circuit tightness of the evaporators being cleaned. The applied chemical cleaning technology and the composition of chemical solutions have shown their chemical effectiveness and safety. The experience gained with operation of the BN-600 reactor plant steam generator is generalized. Recommendations on optimizing the monitoring of the OCC main parameters, on-line monitoring of the process, changing the composition of cleaning solution components, and solution reprocessing methods are formulated.