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) Bitte beachten Sie auch die Beispieldatei AREVA_Beispiele auf dem Softwareserver sw_pool.xp. Dort erhalten Sie Hinweise auf die Verwendung von Fotos, Farben und Gestatungselementen. 1) Framatome ANP GmbH, Germany 2) Eletronuclear, Brazil 3) VGB PowerTech, Germany 2006 ISOE International Symposium, Essen, Germany

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

Average Annual Collective Doses at PWR Plants Around the World

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

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

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

Results: Primary Coolant Chemistry Data

Zn Concentration of Primary Coolant at Angra 2

Fe Concentration of Primary Coolant at Angra 2

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

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

Results: RCS Surface Activity Values and Dose Rates

Co-60 Hot Leg Surface Activity Data of Siemens PWRs

Co-60 Cold Leg Surface Activity Data of Siemens PWRs

Hot Leg Average Contact Dose Rates at Siemens Plants

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

Dose Rate in SG Channel Head of Siemens PWR Hot Leg

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

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.