Thermodynamic modeling of secondary-side water chemistry in PWR steam generator

This study presents a thermodynamic modeling framework to predict secondary-side water chemistry in pressurized water reactors (PWRs), incorporating coupled ionization, liquid-vapor phase partitioning, and thermal decomposition processes within steam generators. The model formulates mass balance and chemical equilibrium equations for hydrazine, ethanolamine, and ammonia, solving them iteratively in conjunction with a recirculating steam generator mass balance. This approach evaluates species concentrations and pH at feedwater, blowdown, and main steam locations under steady-state conditions. Verification confirms that the proposed method yields numerically stable and self-consistent solutions, demonstrating physical consistency under representative operating conditions. Comparison with reported plant data reveals that incorporating thermal decomposition improves prediction accuracy for hydrazine, ethanolamine, and blowdown ammonia. However, accurate agreement with plant data requires site-specific decomposition parameters, as a single fixed value cannot universally represent the variability across different operating conditions. Overall, this study provides a transparent and independently implementable computational foundation for predicting secondary-side water chemistry in PWR steam generators.