Operating the Gentilly-2 Steam Generating System Without Hydrazine Addition

Abstract

The Gentilly-2 plant is a CANDU 600 operating in the province of Quebec. For the past two years the feedwater and steam generators have been operating with all volatile treatment using morpholine and has operated without hydrazine addition, This paper reviews the operating experience of the Gentilly 2 feedwater system and the steam generators. The Gentilly-2 steam and feedwater system has an all ferrous feedtrain which includes a deaerator but has admiralty brass condenser tubes. The operating staff became concerned about decomposition of the hydrazine to ammonia and attack of ammonia on the condenser tubes. As a result of this the operating staff decided to halt hydrazine addition and to determine if the system experienced any problem due to the lack of hydrazine. After 2 years of operation it has been seen that the system continues to operate within the specified chemistry limits. In addition, inspection of the system shows that there has been no evidence of increased corrosion product transport and that the deaerator storage tank and the steam generators have not had any significant crud buildup. This experience indicates that an all ferrous system may operate without hydrazine addition with out experiencing deleterious effects. However, this does not imply that hydrazine addition is without benefit. The system performance will continue to be monitored and attempts will be made to determine whether the corrosion products being produced at Gentilly 2 are significantly different from other plants operating with hydrazine.