Results of Application of Ammonia-Ethanolamine Water Chemistry in the Secondary Circuit of Power Units with a VVER-1200 Reactor

Abstract

The potential scope of application of the ammonia-ethanolamine water chemistry in the secondary circuit of a nuclear power plant (NPP) with a VVER-1200 reactor during pilot commercial operation and normal operation is examined. The water chemistry conditions during pilot commercial operation is controlled by an individual scenario for preparing the power unit for commissioning. An initial high content of iron in the steam generator feedwater is observed at all nuclear power plants. Dosing corrective reagents (such as ammonia, hydrazine, and ethanolamine) at NPP power units VVER-1200 reactors maintains their recommended concentrations and the pH range in the feedwater and blowdown water of the steam generators. A comparative analysis of the water chemistries at NPPs with VVER-1000 and VVER-1200 reactors has revealed no considerable differences between corresponding water chemistries as to the regularities of mass transfer of corrosion products, previously identified dependences of iron concentrations on pH, and their changes with time. A new factor is a sharp decrease in the iron concentrations in the steam generator feedwater (below 1 μg/dm³) at рН₂₅ above 9.45 and in an electrical conductivity of the H-cation treated feedwater sample below 0.3 μS/cm. With the selected water-chemistry and the temperature and heat flux maintained at the VVER-reactor, the factors limiting formation of deposits on the heat-transfer tubes of the steam generator are the concentration of iron products and pH of the working fluid. Data on the fouling of heat-transfer tubes of the steam generator suggest that a stable water chemistry in the secondary circuit allows us to schedule much longer washing intervals for the VVER-1200 steam generators in comparison with those for other VVER-reactors. A further reduction in the mass transfer of corrosion products can be attained by replacing pearlitic steels with low-alloy steels having a chromium content of 1.5 to 2.5% for the manufacture of steam pipelines and individual sections of the feedwater path downstream of the deaerator. The results of operation comply with the main conclusions that were made in developing a model for prediction of corrosion and mass transfer in the secondary circuit of a VVER-reactor and corroborate the feasibility of its application in the design and analysis of water chemistry data during operation of the power unit.