Model Boiler Inhibition Studies of the Nuclear Steam Generator Denting Phenomenon

The buildup of an insoluble corrosion product in the annulus between the tube-to-tube-support-plate in some operating nuclear steam generators has resulted in a deformation or “denting” of the heat transfer tubes. A series of tests were initiated in single-tube model boilers to investigate the denting corrosion process and to determine additives and practices that would arrest this corrosion process. Test results show that properly administered additions of boric acid, sodium phosphate, or calcium hydroxide are capable of stopping the corrosion process leading to denting. Furthermore, it was determined that additions of either boric acid or lithium borate are effective in dent prevention, and this was demonstrated by adding contaminants and inhibitor simultaneously to a nondented test specimen.