Eddy current and visual inspections in PWR steam generators have shown fouling at the upper bundle freespan and support plates, and sludge piles on top of the tubesheet These deposits may create an aggressive environment which is responsible for cracking of tubes and eventually leads to tube failures. Some of the most important factors affecting the fouling process are the steam quality and local velocities. Stagnant flow regions that have liquid entering but mostly vapour leaving may have sludge accumulation due to boiling and/or gravitational settling. The thermal hydraulic performance of the PWR steam generators were analyzed using the 3-D computer code ATHOSBWI. The criteria to identify the potential deposition regions in the tube bundle and on top of the tubesheet are based on predicted qualities and velocities. These regions were compared with field measurements as well as predictions made by other methods. Six different types of steam generators were analyzed. The results showed that increasing the circulation rate will increase the velocity and reduce the steam quality in the upper U-bend region and consequently, reduce the risk of sludge deposition.
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