Assessment Of Polyacrylic Acid Injection To Reduce Sludge And Enhance Thermal Performance Recovery At Nuclear Stations
By Danial Soorty
The accumulation of corrosion product deposits on heated surfaces can promote localized corrosion events and loss of thermal efficiency in pressurized water reactor (PWR) steam generators. Southern Nuclear Operating Co.’s Plant Farley initiated injection of polyacrylic acid (PAA) into final feedwater to combat iron deposition in the steam generators (SGs). Significant thermal margin recovery has been observed, along with an increase in steam generator blowdown iron removal rates. Plant Farley is the first plant operating with manual governor valve control to inject PAA. Along with an improvement in SG heat transfer efficiency, a distinct system response from plants operating with automatic governor valve control was evident. Additionally, Plant Farley is also the first plant to begin injection of PAA into condensate pump discharge. A summary of the experience injecting into condensate pump discharge, along with the distinct system responses at Plant Farley are evaluated in this article.
Dispersant places a surface charge on iron oxide particles, causing them to repel. This action inhibits the ability of the iron oxide particles to agglomerate (form larger particles) and inhibits deposition on heat transfer surfaces such as steam generator tubes. Lower deposition and accumulation of iron oxide in the steam generators reduces the need to sludge lance, reduces the effects of under deposit corrosion, and can potentially increase the efficiency of the steam generator. In addition, the penalties accrued for high feedwater iron concentrations in the INPO Chemistry Effectiveness Index (CEI), can be minimized in the presence of dispersant injection. Farley Nuclear Plant (Farley) has the potential to experience high feedwater iron values, especially upon startup per FNP operational experience.
Dispersant injection has helped to minimize iron transport to the generators during power operations and startup, and also reduce the potential to accrue CEI points for feedwater iron. Improvements in steam generator thermal performance have also been observed following dispersant injection, as observed at other dispersant injecting plants. Dispersant injection commenced following main turbine roll during startup from 2R23 on unit 2 followed by 1R26 on Unit 1.
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