Predicting and Managing Steam Generator Performance

Abstract

To efficiently manage the life of the steam generators (SGs), utilities require ‘tools’ to monitor and assess the effects of degradation and aging, as well as to predict the impact of such degradation on SG performance. To assist utility staff in these areas, AECL has developed a comprehensive ‘tool set’ for steam generator life cycle management. The toolset includes THIRST, a code originally developed to model two-phase flow within a Recirculating Steam Generator (RSG) but now modified to calculate SG bulk water chemistry and the impact of fouling on the SG thermalhydraulic conditions, and SLUDGE, a code developed to predict the SG fouling rate and deposit distribution as a function of operating conditions. Work is currently in progress to map the deposit distribution as part of the normal SG Non-Destructive Examination (NDE) inspections, thus closing the loop between THIRST/SLUDGE predictions and the results of tube-bundle inspection. To ensure that chemistry conditions are optimal throughout the steam cycle, ChemSolv was developed to calculate pH in SG crevice regions and on wetted surfaces throughout the steam cycle. Investigations using electrochemical methods have defined ‘safe zones’, regions of pH and electrochemical corrosion potential where the risk of localized corrosion of the SG tubes is minimized, that in combination with ChemSolv provide a powerful tool for managing steam cycle chemistry.