The Thirst Chemistry Module as a Tool to Determine Optimal Steam Generator Corrosion Control Strategies

Abstract

As a coordinated program, AECL is developing a set of tools to aid with the prediction and management of steam generator performance. THIRST (Thermal Hydraulic Analysis In Recirculating STeam Generators) is a computational tool used for the prediction of steam generator thermalhydraulic performance. THIRST results have been applied successfully to predict thermal degradation, tube vibration and fretting, and flow-accelerated corrosion degradation. A new chemistry module has been added to THIRST, which now makes this code useful for the prediction of local water chemistry parameters in the steam generator. The THIRST chemistry module is comprised of a multicomponent, multiphase mass transport model coupled with a multiphase chemical equilibrium model. As input, the module requires amine concentrations in the feedwater and reheater drains. The module predicts local distributions of amine concentration in the secondary side. The concentration predictions of the module are used to compute the pH by assuming equilibrium between the liquid and gas phases. The chemistry module was verified against results of other work in the literature. The module was used to perform corrosion control assessments for a steam generator with an internal preheater. Five different amines were tested for their ability to maintain high pH to protect against flow-accelerated corrosion. These amines, namely hydrazine, ammonia, ethanolamine, dimethylamine, and morpholine, were compared for their effectiveness in steam generators designed with internal preheaters.