2. Operational Experience with Zinc Injection at Angra 2
B. Stellwag 1), M. Ruebenich 2), M. de Oliveira 2) M. Menezes 2), V. Schneider 1), U. Staudt 3)
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1) Framatome ANP GmbH, Germany
2) Eletronuclear, Brazil
3) VGB PowerTech, Germany
2006 ISOE International Symposium, Essen, Germany

3. Contents Zn Injection at Angra 2: Background and Objective
Preparatory Work
Results: - Primary Coolant Chemistry Data - RCS Surface Activity Data - Dose Rate Trends
Summary and Conclusions

4. Average Annual Collective Doses at PWR Plants Around the World

5. Background and Objective
Stellites in RPV of pre-Konvoi and Konvoi plant generations were substituted by Co-free wear resistant materials
Measure resulted in very low radiation fields at RCS.
Stellites in RPV of Angra 2 similar to four-loop 1300 MW class Siemens PWRs which went commercial in 80´ies
Zinc injection was implemented at Angra 2 for mitigation of future buildup of high dose rates at the RCS
Zinc injection started two days after first criticality of Angra 2

6. Angra 1 and 2 / Brazil April 2002
Angra 2: 1356 MWe four-loop PWR built by Siemens, 1st Criticality 07/2000

7. Preparations for Zinc Injection at Angra 2
Dosing concept: Injection of zinc acetate by chemical injection system
Use of zinc, depleted in Zn-64 (< 5% Zn-64)
Zinc analysis by graphite-tube atomic absorption spectrometry
Analysis frequency for Zn and Fe initially once per day, for Cr and Ni once per week, monitoring of coolant activity
Target concentration 5 ppb Zn in primary coolant
Zinc injection started during commissioning of Angra 2 in Phase D, power tests

8. Results: Primary Coolant Chemistry Data

9. Zn Concentration of Primary Coolant at Angra 2

10. Fe Concentration of Primary Coolant at Angra 2

11. Co-58 & Co-60 Activity Data of Primary Coolant at Angra 2

12. Summary: Coolant Chemistry Properties
Zinc could be detected already at the start of zinc injection
Target of 5 ppb Zn reached 4 weeks later
Avg. coolant Fe concentration of 1.2 ppb Fe is at the lower end of the range typical of Siemens plants
Co-60 content of primary coolant at Angra 2 is lower than that of sister plants despite of lower Co-60 pickup of RCS surfaces
Angra 2 primary coolant chemistry Fe and Co-60 levels can be taken as an indicator for low corrosion product release and hence high-quality oxide layers on RCS materials

13. Results: RCS Surface Activity Values and Dose Rates

14. Co-60 Hot Leg Surface Activity Data of Siemens PWRs

15. Co-60 Cold Leg Surface Activity Data of Siemens PWRs

16. Hot Leg Average Contact Dose Rates at Siemens Plants

17. Cross-Over Piping Avg. Contact Dose Rates at Siemens Plants

18. Dose Rate in SG Channel Head of Siemens PWR Hot Leg

19. Summary: RCS Dose Rates and Surface Activities
Zn injection at Angra 2 resulted in a Co-60 surface activity level in the range of pre-Konvoi and Konvoi plants
RCS contact dose rates and SG channel head data at Angra 2 are also in the range of pre-Konvoi and Konvoi plants
Angra 2 dose rates are at least three times lower than that of sister plants with similar stellite inventory

20. Conclusions, Recommendations
Angra 2 is the first and only PWR plant injecting zinc from start of first criticality
Low Fe and Co-60 levels of primary coolant, hence - low corrosion product release - high quality oxide layers on RCS materials
Results of zinc injection met all of the expectations of the operator of Angra 2
Full-system decontamination and subsequent zinc injection is an attractive option for reducing RCS dose rates of mature PWR plants - quickly - efficiently - permanently.