Environmental Consequences of Using Ammonia-Ethanolamine Water Chemistry in the Secondary Circuit of VVER-1200 Nuclear Power Plants

Abstract

The ammonia-ethanolamine water chemistry used at NPPs with VVER-1200 ensures low rates of corrosion, mass transfer, and growth of corrosion product deposits. The content of corrosion products in the feedwater of the steam generator is less than 1 μg/dm³. This significantly increases the period between flushing the steam generator to remove deposits. However, ethanolamine and ammonia are absorbed by the cation exchange resin in the ion-exchange filters of the secondary circuit purification systems, which leads to the need to regenerate the cation exchange resin and continuously dose reagents to maintain the required pH value in the feedwater. Waste solutions from regeneration containing ethanolamine and large amounts of ammonia must be treated to ensure that the concentrations of these substances do not exceed maximum permissible values when discharged into the environment. To remove ethanolamine and ammonia from regeneration solutions, special installations are created, the operation of which is based on various principles. A pilot plant for cleaning regeneration solutions was manufactured and installed at the Belarusian NPP with VVER-1200. An analysis of the pilot plant’s operation showed that it successfully fulfills its function of protecting the aquatic environment but, at the same time, it is forced to release a significant amount of ammonia into the surrounding air. Removing ammonia is energy-consuming, environmentally unsafe, and requires the additional use of chemical reagents. In this regard, the water-chemical regime of the secondary circuit without ammonia is very promising. Possible options could be either switching from ammonia to dimethylamine or using ethanolamine as the only corrective reagent with the replacement of some of the structural materials of the secondary circuit with steels with a high chromium content, which have higher corrosion resistance compared to those currently used. Both options will simplify the wastewater treatment technology and reduce the environmental impact while maintaining the low corrosion rates achieved by using the ammonia–ethanolamine water chemistry.