Solubility and Mobility of PB-bearing Species Under CANDU Steam Generator Conditions

Abstract

As part of a coordinated program, AECL is developing a set of tools to aid with the prediction and management of steam generator (SG) performance. One important mode of degradation within SGs is intergranular and transgranular stress corrosion cracking (SCC) of SG tubing. Numerous and extensive laboratory studies have demonstrated a definite link between lead and SCC. The prediction of the SG degradation is hindered by the lack of reliable thermodynamic data on the solubilities of lead compounds under SG operating conditions. For lead induced SCC to occur, lead needs to be transported to the metal-oxide interface on the SG tube. AECL has been developing a model to predict such a transport of lead towards (or away from) the metal interface. If the direction of the lead transport can be predicted as a function of water chemistry conditions, practical means of dealing with SG contamination with Pb could be devised and Pb-SCC could be mitigated by appropriate adjustment of the water chemistry. The solubilities for the relevant Pb-bearing species under SG operating conditions are necessary for the application of this model. However, the lack of reliable thermodynamic data make it difficult to calculate the solubilities of lead compounds in typical SG under-deposit environments. In this paper, the experimental method used for the determination of Pb solubility is presented and the preliminary experimental results for lead sulphate are given as a function of temperature and ionic strength under the range of conditions relevant to CANDU SGs.