Framatome ANP - AREVA

Depleted Zinc: A ProactiveSolution to Dose ConcernsDepleted zinc has been usedin BWRs since the 1980sfor dose reduction. More recently,PWRs have used natural zincto mitigate primary water stresscorrosion cracking PWSCC) anddepleted zinc for dose reduction.Recently, depleted zinc has beenshown to prevent the significantsource term increase that followsa steam generator (SG) replacement.Since more and more plants willbe replacing their SGs for longeroperating life, this relatively simplechemical addition can help maintainstable dose levels.Replacement steam generators usematerials more resistant to PWSCCand other corrosion issues. However,as a result, they contain moretube surfaces than those they arereplacing. Moreover, they releasea large amount of unoxidized materialinto the primary system after restartof the plant due to the formationand growth of the oxide film. Thenet effect of this is that once thereplacement SGs are put into service,dose levels can more than double.Framatome ANP recommends thatplants replacing their SGs introducedepleted zinc into their systems one totwo fuel cycles before SG replacementas well as afterwards. This will providemaximum performance and ensurethat any source term increase followingSG replacement is minimized. Oneplant that introduced the depleted zincinto their systems prior to replacingtheir SG did not see any increasein dose levels after the replacement.Another saw a decrease of 17 – 22%after one fuel cycle of additionfollowing their SG replacement. ■Framatome ANPprovides a full lineof zinc productsand services:• In-plant surveillance programs• Injection equipment andanalytical procedures• Feasibility and cost/benefit studies• Plant specific safety andtechnical evaluations• Complete line of zinc productsAdvanced Nuclear Power N O 7 April 2003 21