Depleted zinc has been used in BWRs since the 1980s for dose reduction. More recently, PWRs have used natural zinc to mitigate primary water stress corrosion cracking PWSCC) and depleted zinc for dose reduction. Recently, depleted zinc has been shown to prevent the significant source term increase that follows a steam generator (SG) replacement. Since more and more plants will be replacing their SGs for longer operating life, this relatively simple chemical addition can help maintain stable dose levels.

Replacement steam generators use materials more resistant to PWSCC and other corrosion issues. However, as a result, they contain more tube surfaces than those they are replacing. Moreover, they release a large amount of unoxidized material into the primary system after restart of the plant due to the formation and growth of the oxide film. The net effect of this is that once the replacement SGs are put into service, dose levels can more than double.

Framatome ANP recommends that plants replacing their SGs introduce depleted zinc into their systems one to two fuel cycles before SG replacement as well as afterwards. This will provide maximum performance and ensure that any source term increase following SG replacement is minimized. One plant that introduced the depleted zinc into their systems prior to replacing their SG did not see any increase in dose levels after the replacement. Another saw a decrease of 17 – 22% after one fuel cycle of addition following their SG replacement.

Framatome ANP provides a full line of zinc products and services:

• In-plant surveillance programs
• Injection equipment and analytical procedures
• Feasibility and cost/benefit studies
• Plant specific safety and technical evaluations
• Complete line of zinc products