Using Film-forming Inhibitor Injection to Mitigate Flow Accelerated Corrosion in VVER Secondary Systems

Authors : V.A. Yumranov¹
                 A.N. Kukushkin²

Company : ¹NIKIET N.A. Dolleshal Research and

                     Development Institute of Power 
                     Engineering
                   ²VNIIAM Russian Institute of Nuclear  
                     Power Engineering

Country : Russia

Topics :  

Steam-Water circuit chemistry

ABSTRACT :

The use of film-forming inhibitors is one of the most effective techniques to prevent flow accelerated corrosion at power plants. Film-forming Inhibitors create a diffusion barrier against corrosion aggressive impurity penetration onto metal surfaces. Octadecylamine (ODA) is one of the most advances film-forming inhibitors successfully applied at VVER plants. As a film-forming inhibitor ODA effectively prevents crud accumulation and long-term operation of steam generators at Kola NPP without chemical cleanings. The report highlights the experience with ODA application at VVER plants (Nord, Armenia, Kola, etc.) to protect  carbon steel piping and components  in steam-water circuits during the last 30 years.

Accumulation of corrosion products lead to some problems during long-term operation of VVER plants, such as secondary system component degradation including crud-induced local corrosion. Corrosion sludge and deposit removal from steam generators and other equipment is costly and time-consuming and leads to additional waste production. This problem is vital in the case of plant life extension. Appropriate solutions of the problem could be developed based on both Russian and international experience of the VVER fleet.  Recommendations on how to mitigate corrosion-erosion in VVER secondary systems were developed based on comparative analysis of available long-term data on corrosion product behavior in all the operating VVER plants, such as the following :

• data on sludge and deposit accumulation in inner surfaces of secondary piping and components
• data on corrosion rate measurements using in-situ specimens made from the same structural materials
• data on the efficiency of corrosion product removal from secondary system water by means of condensate polishers and steam generator blowdown cleanup systems
• data on sludge and deposit removal from steam generators during chemical cleaning
• data on secondary piping and components conservation efficiency during  long outages.

Comparative data analysis of corrosion product behavior has shown different corrosion product accumulation rates in Novovoronezh, Кola, Kalinin, Balakovo and Rostov NPPs. The said difference is due to different design and operation peculiarities.