Abstract
The corrosion of steam generator carbon steel internal components results in the formation of the corrosion product, magnetite. In steam generators with cylindrical hole carbon steel tube support plates, the production of magnetite may lead to the phenomenon termed denting, which is the radial constriction of the steam generator tubing at the tube-to-tube support plate intersections. In the formation of magnetite under steam generator operating conditions, hydrogen is released as a by-product. An on-line monitoring technique has been developed to quantify the hydrogen release rates attributed to this corrosion and to provide an indication of the rate of denting progression. The method utilizes the Cambridge Mark IV Dissolved Hydrogen Analyzer to monitor the main steam and feedwater hydrogen concentrations during normal power operations of the plant.
Each source of hydrogen contributing to the total steam generator hydrogen concentration must be quantitatively determined before a close approximation of the corrosion hydrogen can be made. The potential non-steam generator corrosion hydrogen sources are derived from (1) Feedwater, (2) thermal decomposition of hydrazine and (3) primary-to-secondary permeation of hydrogen through the Inconel steam generator tubing. The concept of applying hydrogen monitoring to operating PWR steam generators began in 1976. Based on the work performed to date, it appears that hydrogen monitoring is a useful tool for determining steam generator corrosion levels. Some of the work described in this paper was partially funded by the Electric Power Research Institute, Steam Generator Project Office.
