# Complete analyse of zinc injection impact at BUGEY 2&4

Arancha Tigeras, Frédéric Dacquait, Laure Viricel, Jean-Claude Segura, Luc Guinard, Jean-Luc Bretelle, Alain Rocher

► To cite this version:

Arancha Tigeras, Frédéric Dacquait, Laure Viricel, Jean-Claude Segura, Luc Guinard, et al.. Complete analyse of zinc injection impact at BUGEY 2&4. NPC 2008 - International Conference on Water Chemistry of Nuclear Reactors Systems, Sep 2008, Berlin, Germany. cea-04474041

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Distributed under a Creative Commons Attribution 4.0 International License
Complete analyse of zinc injection impact at BUGEY
2&4

Arancha Tigeras, Frédéric Dacquait, Laure Viricel, Jean-Claude Segura, Luc

Guinard, Jean-Luc Bretelle, Alain Rocher

► To cite this version:

Arancha Tigeras, Frédéric Dacquait, Laure Viricel, Jean-Claude Segura, Luc Guinard, et al.. Complete analyse of zinc injection impact at BUGEY 2&4. NPC 2008 - International Conference on Water Chemistry of Nuclear Reactors Systems, Sep 2008, Berlin, Germany. cea-04474041

HAL Id: cea-04474041

https://cea.hal.science/cea-04474041v1

Submitted on 22 Feb 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Complete Analyse of Zinc injection impact at BUGEY 2&4

A. Tigeras<fnref n="1" />, F.Dacquait², L. Viricel<fnref n="1" />, J.C.Segura³, L. Guinard³, JL. Bretelle⁴, A. Rocher⁴
¹EDF/CEIDRE, ²CEA/DEN, ³EDF/SEPTEN, ⁴EDF/UNIE.
EDF, CEIDRE, 93206 Saint-Denis, France
arancha.tigeras@edf.fr

## Abstract

Zinc injection at BUGEY 2 and 4 provides a distinctive experience in the world, which can be used for a better understanding of the role of the zinc in the primary coolant and its impact on the radiation fields, fuel and wastes. BUGEY Unit 2 and Unit 4 are two EDF 900 MWe PWRs. The alloy 600 MA Steam Generators of BUGEY 4 have been replaced by alloy 690 TT SGs at the end of cycle 23.

EDF implemented the Zinc injection for the first time in France at BUGEY 2 Cycle 22 four years ago in order to reduce the dose rates. In 2005, the zinc injection was also initiated at BUGEY 4 Cycle 23, during the previous cycle of the steam generator replacement.

The gamma-spectrometry measurements performed at BUGEY on the steam generator tubing and primary pipes for several cycles (before and after the zinc injection) seem to show that the zinc incorporation on the oxide layers is not immediate or uniform in the different portions of the circuits and the dose rate reduction may be influenced by different factors.

The interest of BUGEY feedback is the fact that unlike other units in the world, the zinc injection is the only chemistry modification introduced in the primary coolant: other actions supposed to have a positive effect on radiation fields (pH, lithium concentration increase, fuel cleaning) have not been applied. Thereby the actual benefit due the zinc injection can be evaluated for the units similar to those of BUGEY (with alloy 600 and 690).

This paper gives an overview of the experience gathered at BUGEY during the first cycles of zinc injection and presents the future EDF strategy concerning zinc injection.

## 1. BACKGROUND

The first EDF unit injecting zinc was Bugey 2 in 2004. This unit was selected for having the highest dose rate of the French fleet. Two years later the zinc injection was also implemented in the unit 4 of Bugey with a preventive objective of minimizing core radiation fields before Steam Generator Replacement (Table 1).

The demonstration carried out at Bugey 2 and 4 comprises a complete set of analysis in order to verify the

expected benefit from zinc injection as well as its innocuous effect on fuel cladding and other components of the plants.

After three cycles of injection at Bugey 2 and one cycle at Bugey 4 the results are encouraging and EDF has decided to go on with the injection in these units and extend this practice to other units taking into account the other goals of zinc addition in primary coolant: PWSCC and AOA mitigation.

<table><caption>Table 1: History of Zinc Injection at Bugey 2 and 4</caption><thead><tr><th>Unit</th><th>Cycle</th><th>Beginning of cycle</th><th>End of cycle</th><th>Start of Zn Injection</th><th>Zn Injection Duration</th></tr></thead><tbody><tr><td rowspan="4">BUG2</td><td>22</td><td>28/10/03</td><td>18/02/05</td><td>07/09/04</td><td>5 months<fnref n="1" /></td></tr><tr><td>23</td><td>27/03/05</td><td>10/06/06</td><td>22/06/05</td><td>12 months</td></tr><tr><td>24</td><td>01/08/06</td><td>11/08/07</td><td>26/09/06</td><td>10 months</td></tr><tr><td>25</td><td>10/09/07</td><td>Cycle in progress</td><td>14/01/08</td><td>Cycle in progress</td></tr><tr><td rowspan="2">BUG4</td><td>23</td><td>01/10/05</td><td>24/12/06</td><td>24/01/06</td><td>11 months</td></tr><tr><td>24</td><td>26/06/07</td><td>Cycle in progress</td><td>25/07/07</td><td>Cycle in progress</td></tr></tbody></table>

<footnote n="1">¹ Zinc was added for the last 6 months of cycle 22 (after checking the silica criterion, having verified the absence of AOA and preparing the injection system), the injection was interrupted for three weeks due to difficulties with the measurement device (furnace of atomic absorption spectrometry). During cycle 22, zinc was actually added for five months.</footnote>
# Complete Analyse of Zinc injection impact at BUGEY 2&4

A. Tigeras<fnref n="1" />, F.Dacquait², L. Viricel<fnref n="1" />, J.C.Segura³, L. Guinard³, JL. Bretelle⁴, A. Rocher⁴
¹EDF/CEIDRE, ²CEA/DEN, ³EDF/SEPTEN, ⁴EDF/UNIE.
EDF, CEIDRE, 93206 Saint-Denis, France
arancha.tigeras@edf.fr

## Abstract

Zinc injection at BUGEY 2 and 4 provides a distinctive experience in the world, which can be used for a better understanding of the role of the zinc in the primary coolant and its impact on the radiation fields, fuel and wastes. BUGEY Unit 2 and Unit 4 are two EDF 900 MWe PWRs. The alloy 600 MA Steam Generators of BUGEY 4 have been replaced by alloy 690 TT SGs at the end of cycle 23.

EDF implemented the Zinc injection for the first time in France at BUGEY 2 Cycle 22 four years ago in order to reduce the dose rates. In 2005, the zinc injection was also initiated at BUGEY 4 Cycle 23, during the previous cycle of the steam generator replacement.

The gamma-spectrometry measurements performed at BUGEY on the steam generator tubing and primary pipes for several cycles (before and after the zinc injection) seem to show that the zinc incorporation on the oxide layers is not immediate or uniform in the different portions of the circuits and the dose rate reduction may be influenced by different factors.

The interest of BUGEY feedback is the fact that unlike other units in the world, the zinc injection is the only chemistry modification introduced in the primary coolant: other actions supposed to have a positive effect on radiation fields (pH, lithium concentration increase, fuel cleaning) have not been applied. Thereby the actual benefit due the zinc injection can be evaluated for the units similar to those of BUGEY (with alloy 600 and 690).

This paper gives an overview of the experience gathered at BUGEY during the first cycles of zinc injection and presents the future EDF strategy concerning zinc injection.

## 1. BACKGROUND

The first EDF unit injecting zinc was Bugey 2 in 2004. This unit was selected for having the highest dose rate of the French fleet. Two years later the zinc injection was also implemented in the unit 4 of Bugey with a preventive objective of minimizing core radiation fields before Steam Generator Replacement (Table 1).

The demonstration carried out at Bugey 2 and 4 comprises a complete set of analysis in order to verify the

expected benefit from zinc injection as well as its innocuous effect on fuel cladding and other components of the plants.

After three cycles of injection at Bugey 2 and one cycle at Bugey 4 the results are encouraging and EDF has decided to go on with the injection in these units and extend this practice to other units taking into account the other goals of zinc addition in primary coolant: PWSCC and AOA mitigation.

<table><caption>Table 1: History of Zinc Injection at Bugey 2 and 4</caption><thead><tr><th>Unit</th><th>Cycle</th><th>Beginning of cycle</th><th>End of cycle</th><th>Start of Zn Injection</th><th>Zn Injection Duration</th></tr></thead><tbody><tr><td rowspan="4">BUG2</td><td>22</td><td>28/10/03</td><td>18/02/05</td><td>07/09/04</td><td>5 months<fnref n="1" /></td></tr><tr><td>23</td><td>27/03/05</td><td>10/06/06</td><td>22/06/05</td><td>12 months</td></tr><tr><td>24</td><td>01/08/06</td><td>11/08/07</td><td>26/09/06</td><td>10 months</td></tr><tr><td>25</td><td>10/09/07</td><td>Cycle in progress</td><td>14/01/08</td><td>Cycle in progress</td></tr><tr><td rowspan="2">BUG4</td><td>23</td><td>01/10/05</td><td>24/12/06</td><td>24/01/06</td><td>11 months</td></tr><tr><td>24</td><td>26/06/07</td><td>Cycle in progress</td><td>25/07/07</td><td>Cycle in progress</td></tr></tbody></table>

<footnote n="1">¹ Zinc was added for the last 6 months of cycle 22 (after checking the silica criterion, having verified the absence of AOA and preparing the injection system), the injection was interrupted for three weeks due to difficulties with the measurement device (furnace of atomic absorption spectrometry). During cycle 22, zinc was actually added for five months.</footnote>
## 2. CONDITIONS OF ZINC INJECTION IMPLEMENTATION

The zinc is injected as zinc acetate depleted in ⁶⁴Zn. The zinc concentration target is 10 µg/kg with an expected range between 5 and 15 µg/kg. However, as it is described in [1] [2], the load follow operation (figure 1) in EDF NPPs induces some significant variations and concentrations of about 20 µg/kg have been achieved due to the zinc return into the primary coolant.

During the first cycle of injection at Bugey 2, zinc was only added during the last 5 months due to the high silica concentration at the beginning of the cycle. The beginning of injection has been anticipated in the following cycles of Bugey 2 and 4 due to the frequent dilutions (figure 2) of primary coolant which has induced an increase on boron effluents. After analyzing the feedback of three cycles of injection, EDF and AREVA have performed a fuel evaluation in order to optimize the practice and minimize the possible operating restrictions linked to boron effluents. Bugey 2 and Bugey 4 are low duty plants with low concentrations in Ca, Mg and Al and without experience in AOA. Under these conditions, the international feedback and the experimental/theoretical results indicate that the AOA risk is negligible if the nickel concentration is not significant and the stability conditions are reached before beginning of zinc injection. Taking into account these elements, the specifications applied to Bugey 2 and Bugey 4 have evolved in conformity with the recommendations of AREVA for Low Duty Plants:

- limit nickel concentration 6 µg/kg with a target value of 3 µg/kg

- limit silica concentration of 1.5 mg/kg.

Once the zinc injection has started during the different cycles no difficulty has been reported. In total 8.5 kg Zn was added during the three first cycles of injection at Bugey 2 with a total exposure of 284 ppb-months (Table 2). The zinc incorporated into the Reactor

<table><caption>Table 2: Zinc Injection Evolution</caption><thead><tr><td>Unit</td><td>Cycle</td><td>[Zn]average (µg/kg)</td><td>Exposure (ppb months)</td></tr></thead><tbody><tr><td>BUG2</td><td>22</td><td>5</td><td>25</td></tr><tr><td>BUG 2</td><td>23</td><td>9.7</td><td>116</td></tr><tr><td>BUG 2</td><td>24</td><td>13</td><td>143</td></tr><tr><td>BUG 4</td><td>23</td><td>5.9</td><td>67.8</td></tr></tbody></table>

Cooling System (RCS) surfaces is commonly estimated [3] as the difference between the injected mass and the removed mass. Even if this simplified calculation can be applied for the units without load following, for EDF units this result should be considered only as an indicative maximum (Table 3). The zinc losses during power reductions seem to have an influence on the zinc mechanism incorporation [2].

<figure><img src="image_2.png" /><figcaption>Figure 1: Zinc Evolution in RCS during load follow periods.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Figure 2: SiO₂ evolution in RCS during the cycles of zinc injection</figcaption></figure>

<table><caption>Table 3: Estimation of Zinc Incorporated onto RCS Surfaces</caption><thead><tr><td>Unit</td><td>Cycle</td><td>Injection Duration (months)</td><td>Zinc injected Mass (g)</td><td>Zinc removed mass (g)</td><td>Estimated zinc mass incorporated onto RCS surfaces (g)</td></tr></thead><tbody><tr><td>BUG2</td><td>22</td><td>5</td><td>2515</td><td>264</td><td>2251</td></tr><tr><td>BUG2</td><td>23</td><td>12</td><td>4020</td><td>1360</td><td>2660</td></tr><tr><td>BUG2</td><td>24</td><td>10</td><td>1970</td><td>479</td><td>1491</td></tr><tr><td>BUG4</td><td>23</td><td>11</td><td>4870</td><td>550</td><td>4320</td></tr></tbody></table>
## 2. CONDITIONS OF ZINC INJECTION IMPLEMENTATION

The zinc is injected as zinc acetate depleted in ⁶⁴Zn. The zinc concentration target is 10 µg/kg with an expected range between 5 and 15 µg/kg. However, as it is described in [1] [2], the load follow operation (figure 1) in EDF NPPs induces some significant variations and concentrations of about 20 µg/kg have been achieved due to the zinc return into the primary coolant.

During the first cycle of injection at Bugey 2, zinc was only added during the last 5 months due to the high silica concentration at the beginning of the cycle. The beginning of injection has been anticipated in the following cycles of Bugey 2 and 4 due to the frequent dilutions (figure 2) of primary coolant which has induced an increase on boron effluents. After analyzing the feedback of three cycles of injection, EDF and AREVA have performed a fuel evaluation in order to optimize the practice and minimize the possible operating restrictions linked to boron effluents. Bugey 2 and Bugey 4 are low duty plants with low concentrations in Ca, Mg and Al and without experience in AOA. Under these conditions, the international feedback and the experimental/theoretical results indicate that the AOA risk is negligible if the nickel concentration is not significant and the stability conditions are reached before beginning of zinc injection. Taking into account these elements, the specifications applied to Bugey 2 and Bugey 4 have evolved in conformity with the recommendations of AREVA for Low Duty Plants:

- limit nickel concentration 6 µg/kg with a target value of 3 µg/kg

- limit silica concentration of 1.5 mg/kg.

Once the zinc injection has started during the different cycles no difficulty has been reported. In total 8.5 kg Zn was added during the three first cycles of injection at Bugey 2 with a total exposure of 284 ppb-months (Table 2). The zinc incorporated into the Reactor

<table><caption>Table 2: Zinc Injection Evolution</caption><thead><tr><td>Unit</td><td>Cycle</td><td>[Zn]average (µg/kg)</td><td>Exposure (ppb months)</td></tr></thead><tbody><tr><td>BUG2</td><td>22</td><td>5</td><td>25</td></tr><tr><td>BUG 2</td><td>23</td><td>9.7</td><td>116</td></tr><tr><td>BUG 2</td><td>24</td><td>13</td><td>143</td></tr><tr><td>BUG 4</td><td>23</td><td>5.9</td><td>67.8</td></tr></tbody></table>

Cooling System (RCS) surfaces is commonly estimated [3] as the difference between the injected mass and the removed mass. Even if this simplified calculation can be applied for the units without load following, for EDF units this result should be considered only as an indicative maximum (Table 3). The zinc losses during power reductions seem to have an influence on the zinc mechanism incorporation [2].

<figure><img src="image_2.png" /><figcaption>Figure 1: Zinc Evolution in RCS during load follow periods.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Figure 2: SiO₂ evolution in RCS during the cycles of zinc injection</figcaption></figure>

<table><caption>Table 3: Estimation of Zinc Incorporated onto RCS Surfaces</caption><thead><tr><td>Unit</td><td>Cycle</td><td>Injection Duration (months)</td><td>Zinc injected Mass (g)</td><td>Zinc removed mass (g)</td><td>Estimated zinc mass incorporated onto RCS surfaces (g)</td></tr></thead><tbody><tr><td>BUG2</td><td>22</td><td>5</td><td>2515</td><td>264</td><td>2251</td></tr><tr><td>BUG2</td><td>23</td><td>12</td><td>4020</td><td>1360</td><td>2660</td></tr><tr><td>BUG2</td><td>24</td><td>10</td><td>1970</td><td>479</td><td>1491</td></tr><tr><td>BUG4</td><td>23</td><td>11</td><td>4870</td><td>550</td><td>4320</td></tr></tbody></table>
## 3. REACTOR COOLANT DATA

### 3.1 Cycle monitoring

The ⁵⁸Co and ⁶⁰Co activity is plotted with the zinc concentration in the primary coolant of Bugey 2 (Figure 3a). Zinc is detected when [Zn] > 1 µg/kg, during the first cycle of injection after 35 days of injection and reaches the target concentration (10 µg/kg) after injecting 1800 g of zinc. The ⁵⁸Co and ⁶⁰Co activities evolutions are well correlated with the progress of zinc concentration in the primary coolant. The ⁶⁰Co becomes higher than the detection limit and reaches values of 8 MBq/t at the end of cycle 22, while the ⁵⁸Co evolution is quite similar to zinc evolution and their respective variations are a consequence of power variations. During cycles 23 and 24, the zinc reached the target concentration earlier than during cycle 22: after having injected 588 g and 429 g of zinc during cycles 23 and 24 respectively, the zinc concentration was approximately 10 µg/kg and the initial cobalt level was already higher than that observed in the previous cycle before injecting zinc.

At the end of cycles 22 and 23, the radiocobalt activity increases faster than during the cycle without any modification of zinc rate injection and zinc concentration of the zinc acetate solution (Figure 3a). In fact, this behaviour is not linked to the zinc injection but to the power reduction during stretch-out of cycle. During this period the usual activity increase is due to the release of corrosion products from fuel crud [12][13]. At this point it is relevant to indicate that the activity reached in ⁵⁸Co at Bugey 2 and Bugey 4 stays lower than the typical values measured in other units among EDF NPPs. At the end of cycle 24, it is not observed an acceleration in the evolution of radiocobalt because of the absence of stretch-out period.

<figure><img src="image_4.png" /><figcaption>Figure 3a: Correlation between [Zn] and radiocobalt activity evolution in RCS (⁵⁸Co and ⁶⁰Co) at Bugey 2.</figcaption></figure>

Similar evolutions of reactor coolant of reactor radiochemistry were observed at Bugey 4 during the 1st cycle of zinc injection (Figure 3b).

Nickel concentration remains between 2 and 4 µg/kg during stable operation. At the end of the cycles, during stretch-out, nickel concentration slightly increases to concentrations about 5 µg/kg. During this phase of demonstration, iron has been monitored. Its concentration stayed lower than the detection limit (1 µg/kg) during steady operation and became measurable during stretch out (about 5 µg/kg).

<figure><img src="image_5.png" /><figcaption>Figure 3b: Correlation between [Zn] and radiocobalt activity evolution in RCS (⁵⁸Co and ⁶⁰Co) at Bugey 4.</figcaption></figure>

### 3.2 Shutdown Monitoring

The first cycle of injection at Bugey 2 was characterized by a significant increase in the ⁵⁸Co peak at oxygenation (Figure 4a). Even if during the first cycles of injection an increase in the activities was expected according to the international feedback [3] [4], this important peak seemed to be also due to other factors: the increase of the cycle length (from 12 months to 16 months), purification difficulties during some phases of the shutdown and fast [H₂] decrease. After the 3rd cycle of injection the activity values became comparable with the values measured before the beginning of the injection. Concerning the ⁶⁰Co, the peak activity was also significantly higher and stayed after cycle 24 (Figure 4b, 4c), three times higher than the values measured in cycles prior the beginning of zinc injection.

The feedback from Bugey 4 (Figure 4d) confirms the relevant evolution in ⁶⁰Co activity (3050 MBq/t). As expected, the increase in ⁵⁸Co peak (168000 MBq/t) was also observed at Bugey 4, but it was not as high as at Bugey 2. This seems to confirm the influence of the other factors identified at Bugey 2 cycle 22 on ⁵⁸Co activity (Table 4).

The maximum obtained values of nickel and iron at oxygenation are not abnormal compared with other units of EDF fleet without zinc. They remain globally similar after three cycles of injection: about 4500 µg/kg for nickel and 92 µg/kg for iron. Nevertheless, according to the international feedback a reduction of nickel release during the shutdown is expected after some cycles of injection [3].
## 3. REACTOR COOLANT DATA

### 3.1 Cycle monitoring

The ⁵⁸Co and ⁶⁰Co activity is plotted with the zinc concentration in the primary coolant of Bugey 2 (Figure 3a). Zinc is detected when [Zn]>1 µg/kg, during the first cycle of injection after 35 days of injection and reaches the target concentration (10 µg/kg) after injecting 1800 g of zinc. The ⁵⁸Co and ⁶⁰Co activities evolutions are well correlated with the progress of zinc concentration in the primary coolant. The ⁶⁰Co becomes higher than the detection limit and reaches values of 8 MBq/t at the end of cycle 22, while the ⁵⁸Co evolution is quite similar to zinc evolution and their respective variations are a consequence of power variations. During cycles 23 and 24, the zinc reached the target concentration earlier than during cycle 22: after having injected 588 g and 429 g of zinc during cycles 23 and 24 respectively, the zinc concentration was approximately 10 µg/kg and the initial cobalt level was already higher than that observed in the previous cycle before injecting zinc.

At the end of cycles 22 and 23, the radiocobalt activity increases faster than during the cycle without any modification of zinc rate injection and zinc concentration of the zinc acetate solution (Figure 3a). In fact, this behaviour is not linked to the zinc injection but to the power reduction during stretch-out of cycle. During this period the usual activity increase is due to the release of corrosion products from fuel crud [12][13]. At this point it is relevant to indicate that the activity reached in ⁵⁸Co at Bugey 2 and Bugey 4 stays lower than the typical values measured in other units among EDF NPPs. At the end of cycle 24, it is not observed an acceleration in the evolution of radiocobalt because of the absence of stretch-out period.

<figure><img src="image_4.png" /><figcaption>Figure 3a: Correlation between [Zn] and radiocobalt activity evolution in RCS (⁵⁸Co and ⁶⁰Co) at Bugey 2.</figcaption></figure>

Similar evolutions of reactor coolant of reactor radiochemistry were observed at Bugey 4 during the 1st cycle of zinc injection (Figure 3b).

Nickel concentration remains between 2 and 4 µg/kg during stable operation. At the end of the cycles, during stretch-out, nickel concentration slightly increases to concentrations about 5 µg/kg. During this phase of demonstration, iron has been monitored. Its concentration stayed lower than the detection limit (1 µg/kg) during steady operation and became measurable during stretch out (about 5 µg/kg).

<figure><img src="image_5.png" /><figcaption>Figure 3b: Correlation between [Zn] and radiocobalt activity evolution in RCS (⁵⁸Co and ⁶⁰Co) at Bugey 4.</figcaption></figure>

### 3.2 Shutdown Monitoring

The first cycle of injection at Bugey 2 was characterized by a significant increase in the ⁵⁸Co peak at oxygenation (Figure 4a). Even if during the first cycles of injection an increase in the activities was expected according to the international feedback [3] [4], this important peak seemed to be also due to other factors: the increase of the cycle length (from 12 months to 16 months), purification difficulties during some phases of the shutdown and fast [H₂] decrease. After the 3rd cycle of injection the activity values became comparable with the values measured before the beginning of the injection. Concerning the ⁶⁰Co, the peak activity was also significantly higher and stayed after cycle 24 (Figure 4b, 4c), three times higher than the values measured in cycles prior the beginning of zinc injection.

The feedback from Bugey 4 (Figure 4d) confirms the relevant evolution in ⁶⁰Co activity (3050 MBq/t). As expected, the increase in ⁵⁸Co peak (168000 MBq/t) was also observed at Bugey 4, but it was not as high as at Bugey 2. This seems to confirm the influence of the other factors identified at Bugey 2 cycle 22 on ⁵⁸Co activity Table 4).

The maximum obtained values of nickel and iron at oxygenation are not abnormal compared with other units of EDF fleet without zinc. They remain globally similar after three cycles of injection: about 4500 µg/kg for nickel and 92 µg/kg for iron. Nevertheless, according to the international feedback a reduction of nickel release during the shutdown is expected after some cycles of injection [3].
The most important difference between Bugey feedback and international experience is the release of zinc observed during the oxygenation process. Figure 4 represents the monitoring of zinc during the shutdowns. The peaks obtained at Bugey 2 (cycles 22 and 23) and Bugey 4 (cycle 23) are twice as high as the highest peak reported until now (300 µg/kg). This significant release may be explained by differences in the core design with

the other units or/and by the influence of load following during the cycles. It should be noted that during the shutdown of Bugey 2 cycle 24 the peak had significantly decreased to 60 µg/kg.

<table><caption>Table 4: Cobalt activity evolution at Oxygenation during shutdowns before and after Zinc injection at Bugey 2</caption><thead><tr><th>Cycles before injection</th><th><sup>58</sup>Co peak (MBq/t)</th><th><sup>58</sup>Co average peak before injection (MBq/t)</th><th><sup>60</sup>Co peak (MBq/t)</th><th><sup>60</sup>Co average peak before injection (MBq/t)</th></tr></thead><tbody><tr><td>Cycle 20</td><td>152200</td><td rowspan="2">138100</td><td>800</td><td rowspan="2">800</td></tr><tr><td>Cycle 21</td><td>124000</td><td>800</td></tr><tr><th>Cycles after injection</th><th><sup>58</sup>Co peak (MBq/t)</th><th>Ratio <sup>58</sup>Co(before Zn)/<sup>58</sup>Co(after Zn)</th><th><sup>60</sup>Co peak (MBq/t)</th><th>Ratio <sup>60</sup>Co(before Zn)/<sup>60</sup>Co(after Zn)</th></tr><tr><td>Cycle 22</td><td>290000</td><td>2.10</td><td>2510</td><td>3.14</td></tr><tr><td>Cycle 23</td><td>160000</td><td>1.16</td><td>2810</td><td>3.51</td></tr><tr><td>Cycle 24</td><td>150800</td><td>1.09</td><td>2566</td><td>3.21</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Figure 4a: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 22.</figcaption></figure>

Shutdown BUG223

<figure><img src="image_7.png" /><figcaption>Figure 4b: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 23</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Figure 4c: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 24</figcaption></figure>

Shutdown BUG 423

<figure><img src="image_9.png" /><figcaption>Figure 4d: Radiocobalt and Zinc evolution during shutdown of Bugey 4 cycle 23</figcaption></figure>
The most important difference between Bugey feedback and international experience is the release of zinc observed during the oxygenation process. Figure 4 represents the monitoring of zinc during the shutdowns. The peaks obtained at Bugey 2 (cycles 22 and 23) and Bugey 4 (cycle 23) are twice as high as the highest peak reported until now (300 µg/kg). This significant release may be explained by differences in the core design with

the other units or/and by the influence of load following during the cycles. It should be noted that during the shutdown of Bugey 2 cycle 24 the peak had significantly decreased to 60 µg/kg.

<table><caption>Table 4: Cobalt activity evolution at Oxygenation during shutdowns before and after Zinc injection at Bugey 2</caption><thead><tr><th>Cycles before injection</th><th><sup>58</sup>Co peak (MBq/t)</th><th><sup>58</sup>Co average peak before injection (MBq/t)</th><th><sup>60</sup>Co peak (MBq/t)</th><th><sup>60</sup>Co average peak before injection (MBq/t)</th></tr></thead><tbody><tr><td>Cycle 20</td><td>152200</td><td rowspan="2">138100</td><td>800</td><td rowspan="2">800</td></tr><tr><td>Cycle 21</td><td>124000</td><td>800</td></tr><tr><th>Cycles after injection</th><th><sup>58</sup>Co peak (MBq/t)</th><th>Ratio <sup>58</sup>Co(before Zn)/<sup>58</sup>Co(after Zn)</th><th><sup>60</sup>Co peak (MBq/t)</th><th>Ratio <sup>60</sup>Co(before Zn)/<sup>60</sup>Co(after Zn)</th></tr><tr><td>Cycle 22</td><td>290000</td><td>2.10</td><td>2510</td><td>3.14</td></tr><tr><td>Cycle 23</td><td>160000</td><td>1.16</td><td>2810</td><td>3.51</td></tr><tr><td>Cycle 24</td><td>150800</td><td>1.09</td><td>2566</td><td>3.21</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Figure 4a: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 22.</figcaption></figure>

Shutdown BUG223

<figure><img src="image_7.png" /><figcaption>Figure 4b: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 23</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Figure 4c: Radiocobalt and Zinc evolution during shutdown of Bugey 2 cycle 24</figcaption></figure>

Shutdown BUG 423

<figure><img src="image_9.png" /><figcaption>Figure 4d: Radiocobalt and Zinc evolution during shutdown of Bugey 4 cycle 23</figcaption></figure>
## 4. FUEL SURVEILLANCE

During the cycle the flux maps did not evidence any indication of AOA and no operating restrictions were identified.

The cores of Bugey 2 and 4 are loaded with Zircaloy 4 fuel assemblies (F/AS) from AREVA.

The fuel performance during the first three cycles of injection at Bugey 2 was evaluated through visual inspections and thickness oxide measurements for 3rd cycle assemblies with the highest burn-up in the core.

Visual examination did not reveal any particularity of these F/AS when compared to F/AS irradiated without zinc injection. Moreover, the oxide thickness measurements performed during the three cycles of demonstration are completely comparable with the data compiled in the past without zinc. Fuel oxide measurements also agreed well with predicted values for Zircaloy cladding.

Based on these results, the absence of acceleration of corrosion on fuel cladding is confirmed and the current model seems to be also qualified to predict the oxide evolution for units with zinc (Figure 5).

<figure><img src="image_10.png" /><figcaption>Figure 5: Measurement of Fuel Oxide Thickness at Bugey 2 with zinc injection compared with data from 900 MWe units without zinc injection.</figcaption></figure>

## 5. EFFLUENTS AND WASTE SURVEILLANCE

The impact of zinc acetate on the environmental has been analyzed by EDF during the demonstrations of Bugey 2 and Bugey 4.

The temporary cobalt activity increase in primary coolant owing to the zinc action onto the oxide surface may have a potential impact on plant waste generation: liquid waste effluents, spent filters and resins. The data from Bugey 2 and 4 confirm the international feedback synthesized in the reference [3]. The radiocobalt increases in primary coolant during the cycle and shutdown do not necessarily imply an increase in the plant radioactive liquid effluents if the correct purification systems operation is assured (figure 6 and 7). Moreover, the use of zinc depleted in ⁶⁴Zn enables to ensure the absence of ⁶⁵Zn in the liquid wastes.

As a consequence of the correct retention of Cobalt by the demineralizers, after the first cycle of injection at Bugey 2, an increase of the percentage of ⁶⁰Co was observed on the filters. Nevertheless, during the following cycles, the radionuclide percentages have been comparable to the standard spectrum. The activities of solid wastes generated during the zinc cycles did not exceed the limit values for guarantying their evacuation.

EDF has also performed an exhaustive analysis of long life radionucleides (RN) in the primary coolant (⁵⁵Fe, ⁶³Ni, ⁹⁴Nb, ¹⁴C, ⁹⁰Sr) in order to ensure that the typical ratios (typical ratio= RN/⁶⁰Co) used by EDF to characterize the solid wastes are still relevant in the presence of zinc. This has been confirmed by the results from Bugey 2 and Bugey 4.

<figure><img src="image_11.png" /><figcaption>Figure 6: ⁵⁸Co contribution in liquid effluents at Bugey</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Figure 7: ⁶⁰Co contribution in liquid effluents at Bugey</figcaption></figure>

## 6. DOSE RATES EVOLUTION AND SURFACE CONTAMINATION

### 6.1 *Experimental results*

The dose rates (Figure 8) measured in the different points of circuits have been correlated with the surface activities (Figure 9) given by gamma spectrometry (EMECC device) [7] performed by the CEA in order to quantify the actual effect of zinc injection on contamination. These contamination measurements have been carried out in the French fleet since 1971. The experience acquired during this period of time in more than 270 campaigns permit to give a high level of confidence to the results.

The contamination at Bugey 2 was frequently monitored in the past, which helps to better identify the possible particularities of Bugey 2 after Zinc injection.

Between cycles 21 and 24 it should be noted:
## 4. FUEL SURVEILLANCE

During the cycle the flux maps did not evidence any indication of AOA and no operating restrictions were identified.

The cores of Bugey 2 and 4 are loaded with Zircaloy 4 fuel assemblies (F/AS) from AREVA.

The fuel performance during the first three cycles of injection at Bugey 2 was evaluated through visual inspections and thickness oxide measurements for 3rd cycle assemblies with the highest burn-up in the core.

Visual examination did not reveal any particularity of these F/AS when compared to F/AS irradiated without zinc injection. Moreover, the oxide thickness measurements performed during the three cycles of demonstration are completely comparable with the data compiled in the past without zinc. Fuel oxide measurements also agreed well with predicted values for Zircaloy cladding.

Based on these results, the absence of acceleration of corrosion on fuel cladding is confirmed and the current model seems to be also qualified to predict the oxide evolution for units with zinc (Figure 5).

<figure><img src="image_10.png" /><figcaption>Figure 5: Measurement of Fuel Oxide Thickness at Bugey 2 with zinc injection compared with data from 900 MWe units without zinc injection.</figcaption></figure>

## 5. EFFLUENTS AND WASTE SURVEILLANCE

The impact of zinc acetate on the environmental has been analyzed by EDF during the demonstrations of Bugey 2 and Bugey 4.

The temporary cobalt activity increase in primary coolant owing to the zinc action onto the oxide surface may have a potential impact on plant waste generation: liquid waste effluents, spent filters and resins. The data from Bugey 2 and 4 confirm the international feedback synthesized in the reference [3]. The radiocobalt increases in primary coolant during the cycle and shutdown do not necessarily imply an increase in the plant radioactive liquid effluents if the correct purification systems operation is assured (figure 6 and 7). Moreover, the use of zinc depleted in ⁶⁴Zn enables to ensure the absence of ⁶⁵Zn in the liquid wastes.

As a consequence of the correct retention of Cobalt by the demineralizers, after the first cycle of injection at Bugey 2, an increase of the percentage of ⁶⁰Co was observed on the filters. Nevertheless, during the following cycles, the radionuclide percentages have been comparable to the standard spectrum. The activities of solid wastes generated during the zinc cycles did not exceed the limit values for guarantying their evacuation.

EDF has also performed an exhaustive analysis of long life radionucleides (RN) in the primary coolant (⁵⁵Fe, ⁶³Ni, ⁹⁴Nb, ¹⁴C, ⁹⁰Sr) in order to ensure that the typical ratios (typical ratio= RN/⁶⁰Co) used by EDF to characterize the solid wastes are still relevant in the presence of zinc. This has been confirmed by the results from Bugey 2 and Bugey 4.

<figure><img src="image_11.png" /><figcaption>Figure 6: ⁵⁸Co contribution in liquid effluents at Bugey</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Figure 7: ⁶⁰Co contribution in liquid effluents at Bugey</figcaption></figure>

## 6. DOSE RATES EVOLUTION AND SURFACE CONTAMINATION

### 6.1 *Experimental results*

The dose rates (Figure 8) measured in the different points of circuits have been correlated with the surface activities (Figure 9) given by gamma spectrometry (EMECC device) [7] performed by the CEA in order to quantify the actual effect of zinc injection on contamination. These contamination measurements have been carried out in the French fleet since 1971. The experience acquired during this period of time in more than 270 campaigns permit to give a high level of confidence to the results.

The contamination at Bugey 2 was frequently monitored in the past, which helps to better identify the possible particularities of Bugey 2 after Zinc injection.

Between cycles 21 and 24 it should be noted:
* The ⁶⁰Co surface activities are practically constant between cycles 21 and 23. Between cycles 23 and 24 a diminution of 12-14% is reported on all the portions of circuits. This decrease corresponds to the natural decay of ⁶⁰Co and consequently it might be assumed that zinc has only contributed to avoid its incorporation on the ex-core surfaces. These diminutions are sometimes observed in other units without zinc; they are, however, only detected in some points of measurement and/or they are only about 5-10%.

* There is not a general tendency for ⁵⁸Co surface activities on the primary system between cycles 21 and 24. On the other hand, between cycles 23 and 24, they are constant on the primary system.

The evolution of cobalt activities between cycle 23 and 24 is relatively well correlated with the evolution of doses rates (Figures 8-9) considering their higher uncertainties (at least 30%):

* On cross-over piping and cold legs the decrease is more significant after cycle 24.

* On hot legs there was a tendency to increase from cycle 20. This trend was reversed after cycle 23 with a diminution of 15% following with a more significant decrease of 30% after cycle 24.

At Bugey 4 only one cycle of injection has been performed. A ⁶⁰Co activity average diminution of 14% has been detected on cross-over piping and steam generators with a 18% decrease of dose rates. In the other parts of the RCS, no significant evolutions have been detected either in deposited activity or in dose rates.

## 6.2 Discussion and Interpretation of results

After 27 months of injection, the positive effect of Zn on surface activities seems to be detected at Bugey 2. Based on the reduction of ⁶⁰Co surface activity (similar to the natural decay), it is supposed that only the 1st mechanism of inhibition [2] probably occurred at Bugey 2. The presence of Zn has probably had a positive influence to avoid a new recontamination onto the surface of the circuits. At Bugey, up to now the Zn may only reduce the pickup of ⁶⁰Co, since the feedback from Bugey does not permit to suppose that the Zn diffusion process into the inner oxide layers (observed in other units [3]) has begun after 3 cycles of injection. Therefore, it is not possible to affirm that the mechanism of Co substitution has occurred in the deepest layers of oxide in Bugey.

Comparing the surface activity measurements from Bugey with the measurements carried out by CEA in German units [6][8], some aspects can be underlined during the first cycles of injection for these units. Figure 9 represents the average activity evolution of the primary system contamination (SG tubes, hot, cold or crossover legs) during the first cycles of injection at Bugey 2, 4 and Biblis B. From German measurements, the following aspects can be underlined:

- the feedback from Biblis B indicates a slow and progressive reduction in ⁶⁰Co activity. The decrease rate

almost corresponds to the radioactive decay. However, we can wonder if the decrease would not have been the same without zinc injection. Indeed, the ⁶⁰Co contamination level in the primary pipes of Biblis-B was similar, or even higher, than the level at BUGEY-2 and, as observed in Figure 9, the ⁶⁰Co contamination had decreased at BUGEY-2 without Zn injection (i.e. before cycle 22). As already explained in 2004 [9], once the abnormal cobalt source was removed (replacement of Inconel 718 fuel spacer grids with increased cobalt content in BUGEY-2 and BIBLIS-B [10]) or exhausted, the ⁶⁰Co contamination decreased significantly by a factor of between 2 and 4 over roughly 10 years<fnref n="2" /> in BUGEY-2 (between cycles 12 and 20) on the primary coolant pipes and this, without zinc injection. It seems that the ⁶⁰Co build-up coming from the remaining sources is low or even negligible compared to the former ⁶⁰Co contamination on the primary coolant pipes.

- EMECC measurements were also performed at Obrigheim. They did not show a ⁶⁰Co contamination reduction after 2 cycles of Zn injection.

This comparison of surface activity measurements and dose rates evolution during the first cycles of zinc injection in German plants seems to indicate a similar behaviour with Bugey feedback, although the aimed Zn content in German PWR primary systems is 5 ppb whereas it is 10-15 ppb in French PWR primary systems. The effect of zinc seems to be slower than in other units in the world. According to the analysis carried out in [2] this behaviour can be due to:

- the age of the units: in fact, Obrigheim, Biblis B, Bugey 2 and 4 are up to now the units where the Zn injection was implanted later in the life of the plant. The thickness of the oxides on RCS surfaces can play a crucial role on the zinc efficiency.

- Power variation perturbations: the zinc injection at German units with frequent mi-cycle shutdowns and power reductions show also similarities with activity and dose rates evolutions from Bugey [2].

In spite of not having obtained the same effects than the majority of the units in the world, the ⁶⁰Co activity evolution measured on the surfaces seems to be correlated correctly with the dose rates evolution and the first benefits started to be observed after cycle 24 of Bugey 2. According to the global experience of German plants [2] [8] and of the other units in the world, a progressive reduction can be expected for the future cycles of Bugey. To make sure of the favourable impact of Zn on the ⁶⁰Co contamination, it is necessary to confirm the decrease in ⁶⁰Co of about 12% after the next cycles of Bugey-2 and after the 1st shutdown of Bugey 4 which has the particular interest of being the first cycle following SGR. This shutdown is planned in July 2008, thereby it is not yet possible to evaluate the zinc injection advantages at Bugey 4.

<footnote n="2">² ⁶⁰Co decay leads to a contamination decrease of about 4 over 10 years.</footnote>
* The ⁶⁰Co surface activities are practically constant between cycles 21 and 23. Between cycles 23 and 24 a diminution of 12-14% is reported on all the portions of circuits. This decrease corresponds to the natural decay of ⁶⁰Co and consequently it might be assumed that zinc has only contributed to avoid its incorporation on the ex-core surfaces. These diminutions are sometimes observed in other units without zinc; they are, however, only detected in some points of measurement and/or they are only about 5-10%.

* There is not a general tendency for ⁵⁸Co surface activities on the primary system between cycles 21 and 24. On the other hand, between cycles 23 and 24, they are constant on the primary system.

The evolution of cobalt activities between cycle 23 and 24 is relatively well correlated with the evolution of doses rates (Figures 8-9) considering their higher uncertainties (at least 30%):

* On cross-over piping and cold legs the decrease is more significant after cycle 24.

* On hot legs there was a tendency to increase from cycle 20. This trend was reversed after cycle 23 with a diminution of 15% following with a more significant decrease of 30% after cycle 24.

At Bugey 4 only one cycle of injection has been performed. A ⁶⁰Co activity average diminution of 14% has been detected on cross-over piping and steam generators with a 18% decrease of dose rates. In the other parts of the RCS, no significant evolutions have been detected either in deposited activity or in dose rates.

## 6.2 Discussion and Interpretation of results

After 27 months of injection, the positive effect of Zn on surface activities seems to be detected at Bugey 2. Based on the reduction of ⁶⁰Co surface activity (similar to the natural decay), it is supposed that only the 1st mechanism of inhibition [2] probably occurred at Bugey 2. The presence of Zn has probably had a positive influence to avoid a new recontamination onto the surface of the circuits. At Bugey, up to now the Zn may only reduce the pickup of ⁶⁰Co, since the feedback from Bugey does not permit to suppose that the Zn diffusion process into the inner oxide layers (observed in other units [3]) has begun after 3 cycles of injection. Therefore, it is not possible to affirm that the mechanism of Co substitution has occurred in the deepest layers of oxide in Bugey.

Comparing the surface activity measurements from Bugey with the measurements carried out by CEA in German units [6][8], some aspects can be underlined during the first cycles of injection for these units. Figure 9 represents the average activity evolution of the primary system contamination (SG tubes, hot, cold or crossover legs) during the first cycles of injection at Bugey 2, 4 and Biblis B. From German measurements, the following aspects can be underlined:

- the feedback from Biblis B indicates a slow and progressive reduction in ⁶⁰Co activity. The decrease rate

almost corresponds to the radioactive decay. However, we can wonder if the decrease would not have been the same without zinc injection. Indeed, the ⁶⁰Co contamination level in the primary pipes of Biblis-B was similar, or even higher, than the level at BUGEY-2 and, as observed in Figure 9, the ⁶⁰Co contamination had decreased at BUGEY-2 without Zn injection (i.e. before cycle 22). As already explained in 2004 [9], once the abnormal cobalt source was removed (replacement of Inconel 718 fuel spacer grids with increased cobalt content in BUGEY-2 and BIBLIS-B [10]) or exhausted, the ⁶⁰Co contamination decreased significantly by a factor of between 2 and 4 over roughly 10 years<fnref n="2" /> in BUGEY-2 (between cycles 12 and 20) on the primary coolant pipes and this, without zinc injection. It seems that the ⁶⁰Co build-up coming from the remaining sources is low or even negligible compared to the former ⁶⁰Co contamination on the primary coolant pipes.

- EMECC measurements were also performed at Obrigheim. They did not show a ⁶⁰Co contamination reduction after 2 cycles of Zn injection.

This comparison of surface activity measurements and dose rates evolution during the first cycles of zinc injection in German plants seems to indicate a similar behaviour with Bugey feedback, although the aimed Zn content in German PWR primary systems is 5 ppb whereas it is 10-15 ppb in French PWR primary systems. The effect of zinc seems to be slower than in other units in the world. According to the analysis carried out in [2] this behaviour can be due to:

- the age of the units: in fact, Obrigheim, Biblis B, Bugey 2 and 4 are up to now the units where the Zn injection was implanted later in the life of the plant. The thickness of the oxides on RCS surfaces can play a crucial role on the zinc efficiency.

- Power variation perturbations: the zinc injection at German units with frequent mi-cycle shutdowns and power reductions show also similarities with activity and dose rates evolutions from Bugey [2].

In spite of not having obtained the same effects than the majority of the units in the world, the ⁶⁰Co activity evolution measured on the surfaces seems to be correlated correctly with the dose rates evolution and the first benefits started to be observed after cycle 24 of Bugey 2. According to the global experience of German plants [2] [8] and of the other units in the world, a progressive reduction can be expected for the future cycles of Bugey. To make sure of the favourable impact of Zn on the ⁶⁰Co contamination, it is necessary to confirm the decrease in ⁶⁰Co of about 12% after the next cycles of Bugey-2 and after the 1st shutdown of Bugey 4 which has the particular interest of being the first cycle following SGR. This shutdown is planned in July 2008, thereby it is not yet possible to evaluate the zinc injection advantages at Bugey 4.

<footnote n="2">² ⁶⁰Co decay leads to a contamination decrease of about 4 over 10 years.</footnote>
<figure><img src="image_13.png" /></figure>

8a.1 : SG Dose Rate Evolutions at Bugey 2

<figure><img src="image_14.png" /><figcaption>Figure 8a.2 : Dose rate around SG shell</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Figure 9a : <sup>60</sup>Co surface activity on the SG tubes</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Figure 8b : Dose rate at the crossover legs</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Figure 9b : <sup>60</sup>Co surface activity on the cold/crossover legs</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Figure 8c : Dose rate at the hot legs</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>Figure 9c : <sup>60</sup>Co surface activity on the hot legs</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>8a.1 : SG Dose Rate Evolutions at Bugey 2</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>BUGEY-2 - Dose rates around the SG shell</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>$^{60}$Co activity deposited on the SG tubes</figcaption></figure>

<caption>Figure 9a : $^{60}$Co surface activity on the SG tubes</caption>

<figure><img src="image_16.png" /><figcaption>Cross-over dose rates evolutions (BUG 2)</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>$^{60}$Co Activity deposited on the cold or crossover legs</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Figure 8c : Dose rate at the hot legs</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>Figure 9c : $^{60}$Co surface activity on the hot legs</figcaption></figure>
Bugey 2 and Bugey 4 have been selected for the zinc demonstration due to their high levels of dose rates in primary coolant. However, the zinc injection presents also an interest for units where decontamination operations of auxiliary circuits are programmed. In fact the international experience, from units injecting zinc after decontamination operations, shows a diminution of the recontamination rate. This can be linked to the zinc contribution to reduce the re-adhesion of ⁶⁰Co onto the surface of primary coolant and to diminish the potential source term which can be transferred to auxiliary systems. The zinc injection may be also then considered as a preventive method of reducing the contamination of auxiliary systems in units with high levels of doses due to ⁶⁰Co [11].

## 6. CONCLUSION AND EDF STRATEGY

The demonstrations of Bugey 2 and 4 allowed to verify some aspects from international feedback and to identify some particularities of EDF NPPs operation.

The first objective of the demonstration has been reached: the innocuous effect of zinc on components, materials, effluents, wastes and fuel was verified.

In terms of benefits, the results of the demonstrations at Bugey 2 and Bugey 4 shows similar dose rates and

surface activities evolutions than the German experience during the first cycles of injection. After the third cycle of injection at Bugey 2 the results are encouraging but need to be confirmed. Therefore, it is expected to obtain at Bugey similar dose reductions than that observed in German plants following the first cycles of injection and in other plants in the world.

Based on the Bugey results and on the international feedback EDF has decided in 2008 to implement the zinc addition on other units than Bugey 2 and Bugey 4, not only to control contamination and dose rates but also to manage a potential AOA risk on future core designs [13] and to mitigate PWSCC. The EDF strategy is illustrated in the diagram of Figure 10. According to this strategy, zinc injection is planned to begin in about 9 more EDF units from 2009 to 2011.

Technical Specifications are been reviewed by EDF with the fuel vendors especially for the progressive implementation of high zinc concentrations up to 39-40 µg/kg for PWSCC mitigation purposes.

At present time, EDF is developing the Guidelines, recommendations and procedures to facilitate in its units the application of zinc injection and the monitoring of parameters request in order to improve the interpretation of results.

<figure><img src="image_20.png" /><figcaption>Figure 10 : Zinc Injection Strategy at EDF</figcaption></figure>
Bugey 2 and Bugey 4 have been selected for the zinc demonstration due to their high levels of dose rates in primary coolant. However, the zinc injection presents also an interest for units where decontamination operations of auxiliary circuits are programmed. In fact the international experience, from units injecting zinc after decontamination operations, shows a diminution of the recontamination rate. This can be linked to the zinc contribution to reduce the re-adhesion of ⁶⁰Co onto the surface of primary coolant and to diminish the potential source term which can be transferred to auxiliary systems. The zinc injection may be also then considered as a preventive method of reducing the contamination of auxiliary systems in units with high levels of doses due to ⁶⁰Co [11].

## 6. CONCLUSION AND EDF STRATEGY

The demonstrations of Bugey 2 and 4 allowed to verify some aspects from international feedback and to identify some particularities of EDF NPPs operation.

The first objective of the demonstration has been reached: the innocuous effect of zinc on components, materials, effluents, wastes and fuel was verified.

In terms of benefits, the results of the demonstrations at Bugey 2 and Bugey 4 shows similar dose rates and

surface activities evolutions than the German experience during the first cycles of injection. After the third cycle of injection at Bugey 2 the results are encouraging but need to be confirmed. Therefore, it is expected to obtain at Bugey similar dose reductions than that observed in German plants following the first cycles of injection and in other plants in the world.

Based on the Bugey results and on the international feedback EDF has decided in 2008 to implement the zinc addition on other units than Bugey 2 and Bugey 4, not only to control contamination and dose rates but also to manage a potential AOA risk on future core designs [13] and to mitigate PWSCC. The EDF strategy is illustrated in the diagram of Figure 10. According to this strategy, zinc injection is planned to begin in about 9 more EDF units from 2009 to 2011.

Technical Specifications are been reviewed by EDF with the fuel vendors especially for the progressive implementation of high zinc concentrations up to 39-40 µg/kg for PWSCC mitigation purposes.

At present time, EDF is developing the Guidelines, recommendations and procedures to facilitate in its units the application of zinc injection and the monitoring of parameters request in order to improve the interpretation of results.

<figure><img src="image_20.png" /><figcaption>Figure 10 : Zinc Injection Strategy at EDF</figcaption></figure>
ACKNOWLEDGEMENTS

The zinc injection analysis at Bugey and the
preparation of its application in other units are the result
of a cooperative work carried out by different groups of
EDF. The collaboration of following persons should be
highlighted:

* Y. Muller, P.Battista and F.Rollandez (EDF/Bugey) for the correct monitoring of the zinc injection permitting to facilitate the application to the other units at EDF.

* J. Audiard (EDF/CEIDRE), for his support concerning the operational and technical issues, feedback analysis and practice improvements

* F.Cattant (EDF/R&D), N.Rupa and D.Deforges (EDF/CEIDRE) for their technical support concerning the zinc impact on materials.

* J. Errera and B.Lantes for their exhaustive analysis of zinc impact on wastes.

* B.Jeannin (EDF/DPN) for his managerial support.

REFERENCES

[1] A.TIGERAS, G.DEBEC et al. "EDF Zinc Injection: Analysis of Power Reduction Impact on the Chemistry and Radiochemistry parameters". *Water Chemistry of Nuclear reactor Systems*, Korea 2006.

[2] A. TIGERAS, B. STELLWAG et al. "Understanding the zinc behavior in PWR primary coolant: a comparison between French and German experience" *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.

[3] "Pressurized Water Reactor Primary Water Zinc Application Guidelines". EPRI, Palo Alto, CA:2006. 1013420

[4] B.BEVERKOG. "The behaviour of zinc in LWR coolant". Water Chemistry of Nuclear Reactors Systems, San Francisco, Oct 2004

[5] 2007 EPRI Zinc Injection Workshop. Westinghouse Analysis. Washington DC, August 2007.

[6] B. StTELLWAG, M. JUERGENSEN, KERNKRAFTWERK OBRIGHEIM GMBH, D. WOLTER "Zinc Injection in German Plants". *Water Chemistry of Nuclear reactor Systems*, Avignon 2002.

[7] R. EIMEKE and S. ANTHONI, "Ensemble de Mesures et d'Etude de contamination des Circuits". *Proceedings de la 7th International Conference on Radiation Shielding*, Bournemouth 12-16 September 1988".

[8] D. WOLTER, M. BASCHNAGEL et al., "Ten Years Zinc Injection for Radiation Field Reduction at the Biblis Power Station", *Water Chemistry of Nuclear Reactor Systems*, Korea 2006.

[9] F. DACQUAIT, L. GUINARD et al. « Status of primary system contamination in French PWRs », *International Conference on Water Chemistry in Nuclear Reactors Systems San Francisco* (2004)

[10] J. HAAG, D. NIEDER, P. SCHNEIDER-KUHNLE, D. WOLTER and B. STELLWAG, "Operational Experience with Zinc Addition in a German PWR", *International Conference on Water Chemistry in Nuclear Power Plants*, Kashiwasaki Tokyo, October 1998,.

[11] F. DACQUAIT, L. GUINARD et al., « Auxiliary System Contamination in French PWRs », *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.

[12] A. TIGERAS, J.L.BRETELLE, E.DECOSSIN "EDF AOA experience: chemical and thermal-hydraulic analysis". Internat Conference on Water Chemistry of Nuclear Reactor Systems. San Francisco 2004.

[13] E.DECOSSIN, O.BREMNES, A.TIGERAS "Axial Offset Anomaly Feedback and R&D modelling studies on EDF cores" *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.
## ACKNOWLEDGEMENTS

The zinc injection analysis at Bugey and the preparation of its application in other units are the result of a cooperative work carried out by different groups of EDF. The collaboration of following persons should be highlighted:

* Y. Muller, P.Battista and F.Rollandez (EDF/Bugey) for the correct monitoring of the zinc injection permitting to facilitate the application to the other units at EDF.

* J. Audiard (EDF/CEIDRE), for his support concerning the operational and technical issues, feedback analysis and practice improvements

* F.Cattant (EDF/R&D), N.Rupa and D.Deforges (EDF/CEIDRE) for their technical support concerning the zinc impact on materials.

* J. Errera and B.Lantes for their exhaustive analysis of zinc impact on wastes.

* B.Jeannin (EDF/DPN) for his managerial support.

## REFERENCES

[1] A.TIGERAS, G.DEBEC et al. "EDF Zinc Injection: Analysis of Power Reduction Impact on the Chemistry and Radiochemistry parameters". *Water Chemistry of Nuclear reactor Systems*, Korea 2006.

[2] A. TIGERAS, B. STELLWAG et al. "Understanding the zinc behavior in PWR primary coolant: a comparison between French and German experience" *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.

[3] "Pressurized Water Reactor Primary Water Zinc Application Guidelines". EPRI, Palo Alto, CA:2006. 1013420

[4] B.BEVERKOG. "The behaviour of zinc in LWR coolant". Water Chemistry of Nuclear Reactors Systems, San Francisco, Oct 2004

[5] 2007 EPRI Zinc Injection Workshop. Westinghouse Analysis. Washington DC, August 2007.

[6] B. StTELLWAG, M. JUERGENSEN, KERNKRAFTWERK OBRIGHEIM GMBH, D. WOLTER "Zinc Injection in German Plants". *Water Chemistry of Nuclear reactor Systems*, Avignon 2002.

[7] R. EIMEKE and S. ANTHONI, "Ensemble de Mesures et d'Etude de contamination des Circuits". *Proceedings de la 7th International Conference on Radiation Shielding*, Bournemouth 12-16 September 1988".

[8] D. WOLTER, M. BASCHNAGEL et al., "Ten Years Zinc Injection for Radiation Field Reduction at the Biblis Power Station", *Water Chemistry of Nuclear Reactor Systems*, Korea 2006.

[9] F. DACQUAIT, L. GUINARD et al. « Status of primary system contamination in French PWRs », *International Conference on Water Chemistry in Nuclear Reactors Systems San Francisco* (2004)

[10] J. HAAG, D. NIEDER, P. SCHNEIDER-KUHNLE, D. WOLTER and B. STELLWAG, "Operational Experience with Zinc Addition in a German PWR", *International Conference on Water Chemistry in Nuclear Power Plants*, Kashiwasaki Tokyo, October 1998,.

[11] F. DACQUAIT, L. GUINARD et al., « Auxiliary System Contamination in French PWRs », *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.

[12] A. TIGERAS, J.L.BRETELLE, E.DECOSSIN "EDF AOA experience: chemical and thermal-hydraulic analysis". *Internat Conference on Water Chemistry of Nuclear Reactor Systems. San Francisco 2004*.

[13] E.DECOSSIN, O.BREMNES, A.TIGERAS "Axial Offset Anomaly Feedback and R&D modelling studies on EDF cores" *Water Chemistry of Nuclear reactor Systems*, Berlin 2008.