# Zinc effect on the primary circuit contamination of a Belgian PWR using the OSCAR V1.3 code

Marie Bultot, Frédéric Dacquait, Etienne Tevissen, Kim Schildermans, Raphaël Lecocq

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Marie Bultot, Frédéric Dacquait, Etienne Tevissen, Kim Schildermans, Raphaël Lecocq. Zinc effect on the primary circuit contamination of a Belgian PWR using the OSCAR V1.3 code. NPC 2016 - 20th International Conference on Water Chemistry of Nuclear Reactor Systems, Oct 2016, Brighton, United Kingdom. cea-04463810

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# Zinc effect on the primary circuit contamination of a Belgian PWR
using the OSCAR V1.3 code

Paper Number: 80

Marie Bultot¹, Frédéric Dacquait¹, Etienne Tevissen¹,
Kim Schildermans², Raphaël Lecocq²

¹CEA, DEN, France

²ENGIE, Laborelec, Belgium

## ABSTRACT

The purpose of the OSCAR code, developed by the CEA in collaboration with EDF and AREVA NP, is to simulate the contamination of the PWR (Pressurized Water Reactor) primary system. The OSCAR code, coupled to its chemistry module PHREEQCEA, allows researchers to analyse the corrosion product behaviour and to calculate the volume and surface activities of a primary system. It synthesizes knowledge and allows us to progress in understanding the phenomena involved in the contamination caused by activated corrosion products.

The OSCAR V1.3 code has been used to simulate the effect of zinc on the primary circuit contamination of a Belgian PWR operated by ENGIE. This paper highlights the physicochemical phenomena involved during a zinc injection. The OSCAR simulation shows that:

* Zinc precipitates on the inner oxide (Cr-rich layer) instead of cobalt showing that zinc has a better affinity than cobalt with chromites (change in the Co equilibrium concentration).

* Cobalt concentration and $ ^{58}Co $ and $ ^{60}Co $ activities increase in the primary coolant and on the outer oxide of both the in-core and out-of-core surfaces (Fe-rich layer). Different plants have observed this increase during the first cycles of Zn injection.

* An antagonist effect exists between the decreasing $ ^{58}Co $ and $ ^{60}Co $ activities of the inner oxide and the increasing activities of the outer oxide, which explains the slight impact of a zinc injection observed by EMECC campaigns.

## INTRODUCTION

The purpose of the OSCAR code, developed by the CEA in collaboration with EDF and AREVA NP, is to simulate the contamination of the PWR primary system (Dacquait et al., 2012). The OSCAR code, coupled to its chemistry module PHREEQCEA (a version of the PHREEQC code (Parkhurst and Appelo, 1999) extended to the PWR temperature range) in combination with a thermodynamic database developed by the CEA (Plancque et al., 2011), allows researchers to analyse the corrosion product behaviour and to calculate the volume and surface activities of a primary system. It synthesizes knowledge and allows us to progress in understanding the phenomena involved in the contamination caused by activated corrosion products.

The OSCAR V1.3 code is used to simulate the effect of zinc injection on the primary circuit contamination during 3 cycles after 22 operating cycles of a Belgian PWR, hereinafter referred to as Reactor A, operated by ENGIE. Firstly we present the simulation of the first 22 cycles of Reactor A without zinc injection and then during the 3 following cycles with zinc. In the last part, we highlight the physical phenomena involved by a zinc injection.
# Zinc effect on the primary circuit contamination of a Belgian PWR
using the OSCAR V1.3 code

Paper Number: 80

Marie Bultot¹, Frédéric Dacquait¹, Etienne Tevissen¹,
Kim Schildermans², Raphaël Lecocq²

¹CEA, DEN, France

²ENGIE, Laborelec, Belgium

## ABSTRACT

The purpose of the OSCAR code, developed by the CEA in collaboration with EDF and AREVA NP, is to simulate the contamination of the PWR (Pressurized Water Reactor) primary system. The OSCAR code, coupled to its chemistry module PHREEQCEA, allows researchers to analyse the corrosion product behaviour and to calculate the volume and surface activities of a primary system. It synthesizes knowledge and allows us to progress in understanding the phenomena involved in the contamination caused by activated corrosion products.

The OSCAR V1.3 code has been used to simulate the effect of zinc on the primary circuit contamination of a Belgian PWR operated by ENGIE. This paper highlights the physicochemical phenomena involved during a zinc injection. The OSCAR simulation shows that:

* Zinc precipitates on the inner oxide (Cr-rich layer) instead of cobalt showing that zinc has a better affinity than cobalt with chromites (change in the Co equilibrium concentration).

* Cobalt concentration and $ ^{58}Co $ and $ ^{60}Co $ activities increase in the primary coolant and on the outer oxide of both the in-core and out-of-core surfaces (Fe-rich layer). Different plants have observed this increase during the first cycles of Zn injection.

* An antagonist effect exists between the decreasing $ ^{58}Co $ and $ ^{60}Co $ activities of the inner oxide and the increasing activities of the outer oxide, which explains the slight impact of a zinc injection observed by EMECC campaigns.

## INTRODUCTION

The purpose of the OSCAR code, developed by the CEA in collaboration with EDF and AREVA NP, is to simulate the contamination of the PWR primary system (Dacquait et al., 2012). The OSCAR code, coupled to its chemistry module PHREEQCEA (a version of the PHREEQC code (Parkhurst and Appelo, 1999) extended to the PWR temperature range) in combination with a thermodynamic database developed by the CEA (Plancque et al., 2011), allows researchers to analyse the corrosion product behaviour and to calculate the volume and surface activities of a primary system. It synthesizes knowledge and allows us to progress in understanding the phenomena involved in the contamination caused by activated corrosion products.

The OSCAR V1.3 code is used to simulate the effect of zinc injection on the primary circuit contamination during 3 cycles after 22 operating cycles of a Belgian PWR, hereinafter referred to as Reactor A, operated by ENGIE. Firstly we present the simulation of the first 22 cycles of Reactor A without zinc injection and then during the 3 following cycles with zinc. In the last part, we highlight the physical phenomena involved by a zinc injection.
SIMULATION OF THE FIRST 22 CYCLES OF REACTOR A WITHOUT ZINC INJECTION

Reactor A is a 3-loop PWR equipped with alloy 690 tubed steam generators from the Steam Generator Replacement (SGR) at cycle 11.

The structure of the primary circuit is described by control volumes using the design data of the reactor (wetted surfaces, hydraulic diameters, material compositions, nominal temperatures...). The operation data (water chemistry, reactor power) is averaged to obtain a few-day step simulation.

As a matter of comparison, we use the surface activities measured with the EMECC device (Eimecke and Anthoni, 1988) during the shutdowns at the end of cycles 9, 14 and 22 and the volume activities measured by ENGIE during power operation (data available from cycle 13). The results focus on the activities of <sup>58</sup>Co and <sup>60</sup>Co because of their major contribution to the dose rates around the primary system. Figure 1 and Figure 2 present the simulation-measurement comparison of <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the primary surfaces (hot legs, crossover legs and hot and cold sides of the Steam Generator (SG) tubing). Figure 3 presents the simulation-measurement comparison of <sup>58</sup>Co and <sup>60</sup>Co volume activities of the primary water during power operation.

There is a relatively good agreement between the simulation and the measurements of the <sup>58</sup>Co and <sup>60</sup>Co deposited activities. The calculated contamination trends are consistent with the measured ones, in particular the variations due to the SGR at the end of cycle 11 (at about 4200 days): there is an increase and then a decrease in the <sup>58</sup>Co contamination. The <sup>60</sup>Co contamination level is lower after SGR.

Figure 3 shows that the calculated <sup>58</sup>Co and <sup>60</sup>Co volume activities during power operation are consistent with the measurements (about 10 Bq/g for <sup>58</sup>Co and between 0.1 and 1 Bq/g for <sup>60</sup>Co). Note that the measured peak volume activities correspond to the cold shutdowns at the end of cycles which have not been modelled accurately in this simulation but their effects have been taken into account by the OSCAR code.

This simulation illustrates the ability of the OSCAR code to simulate the contamination transfer of a reactor during several cycles, given design and operating data.

<figure><img src="image_1.png" /><figcaption>Figure 1. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot legs and crossover legs - Comparison to EMECC measurements.</figcaption></figure>
SIMULATION OF THE FIRST 22 CYCLES OF REACTOR A WITHOUT ZINC INJECTION

Reactor A is a 3-loop PWR equipped with alloy 690 tubed steam generators from the Steam Generator Replacement (SGR) at cycle 11.

The structure of the primary circuit is described by control volumes using the design data of the reactor (wetted surfaces, hydraulic diameters, material compositions, nominal temperatures...). The operation data (water chemistry, reactor power) is averaged to obtain a few-day step simulation.

As a matter of comparison, we use the surface activities measured with the EMECC device (Eimecke and Anthoni, 1988) during the shutdowns at the end of cycles 9, 14 and 22 and the volume activities measured by ENGIE during power operation (data available from cycle 13). The results focus on the activities of <sup>58</sup>Co and <sup>60</sup>Co because of their major contribution to the dose rates around the primary system. Figure 1 and Figure 2 present the simulation-measurement comparison of <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the primary surfaces (hot legs, crossover legs and hot and cold sides of the Steam Generator (SG) tubing). Figure 3 presents the simulation-measurement comparison of <sup>58</sup>Co and <sup>60</sup>Co volume activities of the primary water during power operation.

There is a relatively good agreement between the simulation and the measurements of the <sup>58</sup>Co and <sup>60</sup>Co deposited activities. The calculated contamination trends are consistent with the measured ones, in particular the variations due to the SGR at the end of cycle 11 (at about 4200 days): there is an increase and then a decrease in the <sup>58</sup>Co contamination. The <sup>60</sup>Co contamination level is lower after SGR.

Figure 3 shows that the calculated <sup>58</sup>Co and <sup>60</sup>Co volume activities during power operation are consistent with the measurements (about 10 Bq/g for <sup>58</sup>Co and between 0.1 and 1 Bq/g for <sup>60</sup>Co). Note that the measured peak volume activities correspond to the cold shutdowns at the end of cycles which have not been modelled accurately in this simulation but their effects have been taken into account by the OSCAR code.

This simulation illustrates the ability of the OSCAR code to simulate the contamination transfer of a reactor during several cycles, given design and operating data.

<figure><img src="image_2.png" /><figcaption>Figure 1. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot legs and crossover legs - Comparison to EMECC measurements.</figcaption></figure>
<figure><img src="image_2.png" /><figcaption>Figure 2. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot and cold sides of the SGs - Comparison to EMECC measurements.</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Figure 3. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co volume activities of the primary coolant - Comparison to measurements.</figcaption></figure>

SIMULATION OF THE 3 FOLLOWING CYCLES OF REACTOR A WITH ZINC INJECTION

The OSCAR V1.3 code is used to simulate the effect of zinc on the primary circuit contamination of Reactor A during 3 cycles. Two calculations are performed by adding 3 cycles similar to the 22nd cycle:

* A reference simulation without a zinc injection during those 3 cycles.

* A simulation with a target Zn concentration of 15 ppb during those 3 cycles.
<figure><img src="image_3.png" /><figcaption>Figure 2. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot and cold sides of the SGs - Comparison to EMECC measurements.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Figure 3. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co volume activities of the primary coolant - Comparison to measurements.</figcaption></figure>

SIMULATION OF THE 3 FOLLOWING CYCLES OF REACTOR A WITH ZINC INJECTION

The OSCAR V1.3 code is used to simulate the effect of zinc on the primary circuit contamination of Reactor A during 3 cycles. Two calculations are performed by adding 3 cycles similar to the 22nd cycle:

* A reference simulation without a zinc injection during those 3 cycles.

* A simulation with a target Zn concentration of 15 ppb during those 3 cycles.
Injection rate and zinc concentration

The zinc concentration calculated by using OSCAR of the primary coolant during cycles 23 to 25 is presented in Figure 4. To obtain the target level of 15 ppb after several operating months with zinc injection, the injection rate of zinc, depleted in $^{64}$Zn, is set to the following values:

* 65 g/day during the first 9 months of the 23rd cycle

* 13 g/day during the 11 remaining months of the 23rd cycle

* 12 g/day during the 24th cycle

* 11 g/day during the 25th cycle.

After 150 injection days, the zinc concentration is above 1 ppb and it is stabilized at about 15 ppb after a 280-day duration.

<figure><img src="image_4.png" /><figcaption>Figure 4: OSCAR simulation - Zinc concentration of the primary coolant.</figcaption></figure>

Volume and surface activities

Figure 5 presents the $^{58}$Co, $^{60}$Co and $^{65}$Zn volume activities with and without zinc injection from cycle 23 to cycle 25.

The $^{58}$Co and $^{60}$Co volume activities are twice as high during the zinc injection. An increase in the $^{58}$Co and $^{60}$Co volume activities is commonly observed when zinc is injected in a PWR, for instance see (Tigeras et al., 2008).

The $^{65}$Zn volume activity ranges between 0.2 and 2 Bq/g as the zinc concentration is about 15 ppb, which is consistent with the on-site measurements when zinc is depleted in $^{64}$Zn.
## Injection rate and zinc concentration

The zinc concentration calculated by using OSCAR of the primary coolant during cycles 23 to 25 is presented in Figure 4. To obtain the target level of 15 ppb after several operating months with zinc injection, the injection rate of zinc, depleted in $^{64}$Zn, is set to the following values:

* 65 g/day during the first 9 months of the 23rd cycle

* 13 g/day during the 11 remaining months of the 23rd cycle

* 12 g/day during the 24th cycle

* 11 g/day during the 25th cycle.

After 150 injection days, the zinc concentration is above 1 ppb and it is stabilized at about 15 ppb after a 280-day duration.

<figure><img src="image_5.png" /><figcaption>Figure 4: OSCAR simulation - Zinc concentration of the primary coolant.</figcaption></figure>

## Volume and surface activities

Figure 5 presents the $^{58}$Co, $^{60}$Co and $^{65}$Zn volume activities with and without zinc injection from cycle 23 to cycle 25.

The $^{58}$Co and $^{60}$Co volume activities are twice as high during the zinc injection. An increase in the $^{58}$Co and $^{60}$Co volume activities is commonly observed when zinc is injected in a PWR, for instance see (Tigeras et al., 2008).

The $^{65}$Zn volume activity ranges between 0.2 and 2 Bq/g as the zinc concentration is about 15 ppb, which is consistent with the on-site measurements when zinc is depleted in $^{64}$Zn.
<figure><img src="image_5.png" /><figcaption>Figure 5: OSCAR simulation - <sup>58</sup>Co, <sup>60</sup>Co and <sup>65</sup>Zn volume activities of the primary coolant with or without zinc injection.</figcaption></figure>

To illustrate the impact of zinc injection on the surface contamination of the primary system, Figure 5 presents the comparison between the simulated <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot legs, cold legs, cold side of the SG tube bundles (the impact is practically the same on the SG hot side) and the total <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the fuel rods with and without zinc injection.

When zinc is injected, the <sup>58</sup>Co surface activity increases at the end of cycle regardless of the region and the cycle. For the <sup>60</sup>Co surface contamination, it depends on the region and the cycle. At the end of the first cycle with zinc, there is no significant difference between <sup>60</sup>Co contaminations on the primary loops with and without zinc injection, except on the fuel elements where the <sup>60</sup>Co contamination is higher when zinc is injected; and then the gaps become larger and larger. At the end of the third cycle, the <sup>60</sup>Co activity deposited on the primary surfaces increases with zinc injection, the hot legs excepted.

Table 1 shows the impact of 3 cycles with 15 ppb of zinc on the <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the primary circuit. According to the OSCAR simulation, there is a beneficial impact of zinc on the primary system contamination for the sole <sup>60</sup>Co activity deposited on the hot legs. The impact on the contamination of the out-of-flux surfaces and on the <sup>58</sup>Co contamination of the fuel elements is relatively low after 3 cycles with zinc injection (less than about ±30%). On the other hand, the impact on the <sup>60</sup>Co contamination of the fuel elements is high (about +80%). This impact is consistent with the field experience based on EMECC campaigns which shows that zinc has a slight effect on the contamination of old oxidized surfaces, but a strong increasing effect on the <sup>60</sup>Co contamination deposited on the fuel elements (increase in the <sup>60</sup>Co peak activity during cold shutdown when zinc is injected (Tigeras et al., 2008)).
<figure><img src="image_6.png" /><figcaption>Figure 5: OSCAR simulation - <sup>58</sup>Co, <sup>60</sup>Co and <sup>65</sup>Zn volume activities of the primary coolant with or without zinc injection.</figcaption></figure>

To illustrate the impact of zinc injection on the surface contamination of the primary system, Figure 5 presents the comparison between the simulated <sup>58</sup>Co and <sup>60</sup>Co surface activities on the hot legs, cold legs, cold side of the SG tube bundles (the impact is practically the same on the SG hot side) and the total <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the fuel rods with and without zinc injection.

When zinc is injected, the <sup>58</sup>Co surface activity increases at the end of cycle regardless of the region and the cycle. For the <sup>60</sup>Co surface contamination, it depends on the region and the cycle. At the end of the first cycle with zinc, there is no significant difference between <sup>60</sup>Co contaminations on the primary loops with and without zinc injection, except on the fuel elements where the <sup>60</sup>Co contamination is higher when zinc is injected; and then the gaps become larger and larger. At the end of the third cycle, the <sup>60</sup>Co activity deposited on the primary surfaces increases with zinc injection, the hot legs excepted.

Table 1 shows the impact of 3 cycles with 15 ppb of zinc on the <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the primary circuit. According to the OSCAR simulation, there is a beneficial impact of zinc on the primary system contamination for the sole <sup>60</sup>Co activity deposited on the hot legs. The impact on the contamination of the out-of-flux surfaces and on the <sup>58</sup>Co contamination of the fuel elements is relatively low after 3 cycles with zinc injection (less than about ±30%). On the other hand, the impact on the <sup>60</sup>Co contamination of the fuel elements is high (about +80%). This impact is consistent with the field experience based on EMECC campaigns which shows that zinc has a slight effect on the contamination of old oxidized surfaces, but a strong increasing effect on the <sup>60</sup>Co contamination deposited on the fuel elements (increase in the <sup>60</sup>Co peak activity during cold shutdown when zinc is injected (Tigeras et al., 2008)).
<figure><img src="image_6.png" /><figcaption>Figure 6. OSCAR simulation - <sup>58</sup>Co and <sup>60</sup>Co activities deposited on the hot legs, cold legs, steam generator tubes (cold side) and fuel rods with or without zinc injection.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>Figure 6. OSCAR simulation - ⁵⁸Co and ⁶⁰Co activities deposited on the hot legs, cold legs, steam generator tubes (cold side) and fuel rods with or without zinc injection.</figcaption></figure>
<table><caption>Table 1. Impact of zinc injection on the ⁵⁸Co and ⁶⁰Co activities deposited on the primary surfaces at the end of cycle 25.</caption><thead><tr><th></th><th>⁵⁸Co</th><th>⁶⁰Co</th></tr></thead><tbody><tr><td>Hot legs</td><td>+18%</td><td>-23%</td></tr><tr><td>Cold legs</td><td>+32%</td><td>+34%</td></tr><tr><td>SG hot side</td><td>+28%</td><td>+10%</td></tr><tr><td>SG cold side</td><td>+27%</td><td>+10%</td></tr><tr><td>Fuel rods</td><td>+23%</td><td>+84%</td></tr></tbody></table>

## ANALYSIS OF THE PHYSICOCHEMICAL PHENOMENA IN THE PRESENCE OF ZINC

Due to its great affinity for chromite (Lister, 1992), zinc changes the stability of the chromium-rich solid solution, i.e. the stability of the inner oxide. Zinc greatly incorporates in the inner oxide and has an impact on the equilibrium concentrations of chemical elements, including cobalt in particular, with the inner oxide. In the OSCAR code, the equilibrium concentration of each chemical element and the oxide speciation are calculated by PHREEQCEA. The PHREEQCEA code determines the composition of the ideal solid solution (mixed oxides and any pure solid phases possibly in excess) and the equilibrium concentration of each element in relation to the chemical conditions (pH, H₂, O₂), the coolant temperature and the masses of the metallic elements of the considered oxide in each region. Figure 7 presents the comparison between the Co concentrations in the bulk in equilibrium with the inner oxide of the steam generator tubing calculated by PHREEQCEA with and without zinc injection. The presence of zinc increases the equilibrium concentration of Co in the bulk. This increase results in a change of the system of dissolution/precipitation of Co: cobalt has a tendency to precipitate on the inner oxide until the end of the incubation phase (phase during which Zn greatly precipitates on the inner oxide up to its saturation). It then has a tendency to dissolve after the incubation phase (see Figure 8).

<figure><img src="image_7.png" /><figcaption>Figure 7. OSCAR simulation - Co concentration in the bulk in equilibrium with the inner oxide of the SG tubing cold side with and without zinc injection.</figcaption></figure>
<table><caption>Table 1. Impact of zinc injection on the ⁵⁸Co and ⁶⁰Co activities deposited on the primary surfaces at the end of cycle 25.</caption><thead><tr><th></th><th>⁵⁸Co</th><th>⁶⁰Co</th></tr></thead><tbody><tr><td>Hot legs</td><td>+18%</td><td>-23%</td></tr><tr><td>Cold legs</td><td>+32%</td><td>+34%</td></tr><tr><td>SG hot side</td><td>+28%</td><td>+10%</td></tr><tr><td>SG cold side</td><td>+27%</td><td>+10%</td></tr><tr><td>Fuel rods</td><td>+23%</td><td>+84%</td></tr></tbody></table>

## ANALYSIS OF THE PHYSICOCHEMICAL PHENOMENA IN THE PRESENCE OF ZINC

Due to its great affinity for chromite (Lister, 1992), zinc changes the stability of the chromium-rich solid solution, i.e. the stability of the inner oxide. Zinc greatly incorporates in the inner oxide and has an impact on the equilibrium concentrations of chemical elements, including cobalt in particular, with the inner oxide. In the OSCAR code, the equilibrium concentration of each chemical element and the oxide speciation are calculated by PHREEQCEA. The PHREEQCEA code determines the composition of the ideal solid solution (mixed oxides and any pure solid phases possibly in excess) and the equilibrium concentration of each element in relation to the chemical conditions (pH, H₂, O₂), the coolant temperature and the masses of the metallic elements of the considered oxide in each region. Figure 7 presents the comparison between the Co concentrations in the bulk in equilibrium with the inner oxide of the steam generator tubing calculated by PHREEQCEA with and without zinc injection. The presence of zinc increases the equilibrium concentration of Co in the bulk. This increase results in a change of the system of dissolution/precipitation of Co: cobalt has a tendency to precipitate on the inner oxide until the end of the incubation phase (phase during which Zn greatly precipitates on the inner oxide up to its saturation). It then has a tendency to dissolve after the incubation phase (see Figure 8).

<figure><img src="image_8.png" /><figcaption>Figure 7. OSCAR simulation - Co concentration in the bulk in equilibrium with the inner oxide of the SG tubing cold side with and without zinc injection.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 8. OSCAR simulation - Dissolution and precipitation rates of Co on the inner oxide and on the outer oxide of the SG tubing cold side during cycle 22 (without zinc injection) and during the 3 following cycles with zinc injection - Variation of the Zn mass of the inner oxide of the SG tubing cold side.</figcaption></figure>

It should be pointed out that cobalt always dissolves from the outer oxide (Fe-rich layer) regardless of the concentration of zinc. Zinc thus has no beneficial effect on the outer oxide, i.e. ferrites, as expected and it even has a detrimental effect. We have plotted the $^{60}$Co activity of the inner oxide and the outer oxide of the SG tubing cold side with and without zinc injection in Figure 9. When zinc is injected, the $^{60}$Co activity of the inner oxide (chromites) decreases due to the dissolution of cobalt (see Figure 8). This dissolution concerns not only $^{60}$Co but also the other isotopes of Co including $^{58}$Co and $^{59}$Co which forms $^{60}$Co by neutron activation. Therefore there is a double effect resulting in an increase of Co in the primary coolant: the precipitation of Co on the inner oxide stops and Co dissolves from the inner oxide. A part of this surplus of Co is deposited on the fuel elements leading to an increase in the formation of $^{60}$Co (see Figure 6). This activated deposit is eroded and the particles are deposited on the outer oxide of the out-of-core components, including the SG tubing, resulting in an increase in the $^{60}$Co contamination of this outer oxide (see Figure 9). Thus, there is a decrease in the $^{60}$Co contamination of the inner oxide on the one hand and an increase in the $^{60}$Co contamination of the outer oxide on the other. Depending on the region and time, it results in an increase, decrease or a stagnation of the $^{60}$Co contamination of the out-of-flux surfaces (see Figure 6).
<figure><img src="image_9.png" /><figcaption>Figure 8. OSCAR simulation - Dissolution and precipitation rates of Co on the inner oxide and on the outer oxide of the SG tubing cold side during cycle 22 (without zinc injection) and during the 3 following cycles with zinc injection - Variation of the Zn mass of the inner oxide of the SG tubing cold side.</figcaption></figure>

It should be pointed out that cobalt always dissolves from the outer oxide (Fe-rich layer) regardless of the concentration of zinc. Zinc thus has no beneficial effect on the outer oxide, i.e. ferrites, as expected and it even has a detrimental effect. We have plotted the $^{60}$Co activity of the inner oxide and the outer oxide of the SG tubing cold side with and without zinc injection in Figure 9. When zinc is injected, the $^{60}$Co activity of the inner oxide (chromites) decreases due to the dissolution of cobalt (see Figure 8). This dissolution concerns not only $^{60}$Co but also the other isotopes of Co including $^{58}$Co and $^{59}$Co which forms $^{60}$Co by neutron activation. Therefore there is a double effect resulting in an increase of Co in the primary coolant: the precipitation of Co on the inner oxide stops and Co dissolves from the inner oxide. A part of this surplus of Co is deposited on the fuel elements leading to an increase in the formation of $^{60}$Co (see Figure 6). This activated deposit is eroded and the particles are deposited on the outer oxide of the out-of-core components, including the SG tubing, resulting in an increase in the $^{60}$Co contamination of this outer oxide (see Figure 9). Thus, there is a decrease in the $^{60}$Co contamination of the inner oxide on the one hand and an increase in the $^{60}$Co contamination of the outer oxide on the other. Depending on the region and time, it results in an increase, decrease or a stagnation of the $^{60}$Co contamination of the out-of-flux surfaces (see Figure 6).
<figure><img src="image_9.png" /><figcaption>Figure 9. OSCAR simulation – $^{60}$Co activity of the inner oxide and the outer oxide of the SG tubing cold side with or without zinc injection.</figcaption></figure>

The OSCAR code provides an explanation of some physicochemical phenomena involved in the contamination by activated corrosion products in the presence of zinc. This explanation is in accordance with the assessment of the EMECC campaigns carried out in PWRs in which zinc is injected. It should be pointed out that no specific mechanism has been added to the OSCAR code to reproduce the effect of zinc on the water chemistry (see (Dacquait et al., 2012) for the corrosion product transfer modelling). It should also be noted that the effect of zinc on the corrosion (Harding, 1996) is not taken into account in OSCAR V1.3, but this effect is of second order for old oxidized surfaces such as those of Reactor A. Nevertheless, this effect will be taken into account in OSCAR V1.4 which is scheduled to be released in 2017.

## CONCLUSION

Based on an OSCAR V1.3 simulation, the study of zinc injection in a Belgian PWR shows that:

* Zinc incorporates in the inner oxide (Cr-rich layer) replacing cobalt because of zinc's higher affinity with chromite.

* Cobalt concentration and $^{58}$Co and $^{60}$Co activities increase in the primary coolant and on the outer oxide of both the in-core and out-of-core surfaces (Fe-rich layer).

* An antagonist effect is pointed out between the decreasing $^{58}$Co and $^{60}$Co activities of the inner oxide and the increasing activities of the outer oxide. It explains the slight impact of a zinc injection observed by EMECC campaigns.

## NOMENCLATURE

**EMECC** Ensemble de Mesure et d'Etude de la Contamination des Circuits

**OSCAR** Outil de Simulation de la Contamination en Réacteur

**PWR** Pressurized Water Reactor

**SG** Steam Generator

**SGR** Steam Generator Replacement
<figure><img src="image_10.png" /><figcaption>Figure 9. OSCAR simulation – $^{60}$Co activity of the inner oxide and the outer oxide of the SG tubing cold side with or without zinc injection.</figcaption></figure>

The OSCAR code provides an explanation of some physicochemical phenomena involved in the contamination by activated corrosion products in the presence of zinc. This explanation is in accordance with the assessment of the EMECC campaigns carried out in PWRs in which zinc is injected. It should be pointed out that no specific mechanism has been added to the OSCAR code to reproduce the effect of zinc on the water chemistry (see (Dacquait et al., 2012) for the corrosion product transfer modelling). It should also be noted that the effect of zinc on the corrosion (Harding, 1996) is not taken into account in OSCAR V1.3, but this effect is of second order for old oxidized surfaces such as those of Reactor A. Nevertheless, this effect will be taken into account in OSCAR V1.4 which is scheduled to be released in 2017.

## CONCLUSION

Based on an OSCAR V1.3 simulation, the study of zinc injection in a Belgian PWR shows that:

* Zinc incorporates in the inner oxide (Cr-rich layer) replacing cobalt because of zinc's higher affinity with chromite.

* Cobalt concentration and $^{58}$Co and $^{60}$Co activities increase in the primary coolant and on the outer oxide of both the in-core and out-of-core surfaces (Fe-rich layer).

* An antagonist effect is pointed out between the decreasing $^{58}$Co and $^{60}$Co activities of the inner oxide and the increasing activities of the outer oxide. It explains the slight impact of a zinc injection observed by EMECC campaigns.

## NOMENCLATURE

EMECC Ensemble de Mesure et d'Etude de la Contamination des Circuits

OSCAR Outil de Simulation de la Contamination en Réacteur

PWR Pressurized Water Reactor

SG Steam Generator

SGR Steam Generator Replacement
REFERENCES

Dacquait, F., Francescatto, J., Broutin, F., Genin, J.B., Bénier, G., Girard, M., You, D., Ranchoux, G., Bonnefon, J., Bachet, B. and Riot, G. (2012). "Simulations of corrosion product transfer with the OSCAR V1.2 code", *Proceedings of the Nuclear Plant Chemistry Conference 2012*, 24-28/09/12, Paris (France).

Eimecke, R. and Anthoni, S. (1988). "Ensemble de Mesures et d'Etude de la Contamination des Circuits", *Proceedings of the 7th International Conference on Radiation Shielding*, 12-16 September 1988, Bournemouth (GB), Vol. 1, p.103-113, UKAEA & OECD, Winfrith.

Harding, J.H. (1996). "Modelling the effect of zinc addition on the uptake of cobalt by oxide films in PWRs", *Proceedings of the International Conference on Water Chemistry of Nuclear Reactor System* 7, Bournemouth, 13-17 October 1996.

Lister, D.H. (1992). "Activity transport and corrosion processes in PWRs", *Proceedings of the International Conference on the Water Chemistry of Nuclear Reactor System* 6, 12-15/10/92, Bournemouth (GB), Vol. 2 49-60.

Parkhurst, D.L. and Appelo, C.A.J. (1999). "User's guide to PHREEQC (version 2) - A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations", *Report 99-4259*, US Geological Survey, Denver, Colorado.

Plancque, G., You, D., Blanchard, E., Mertens, V. and Lamouroux, C. (2011). "Role of chemistry in the phenomena occurring in nuclear power plants circuits", *Proceedings of the International Congress on Advances in Nuclear power Plants*, ICAPP, 2-5 May 2011, Nice (France).

Tigeras, A., Dacquait, F., Viricel, L., Segura, J.C., Guinard, L., Bretelle, J.L. and Rocher, A. (2008). "Complete Analyse of Zinc injection impact at BUGEY 2&4", *Proceedings of the International Conference on Water Chemistry of Nuclear Reactors Systems*, 15-18/09/08, Berlin (Germany), 1-32.
REFERENCES

Dacquait, F., Francescatto, J., Broutin, F., Genin, J.B., Bénier, G., Girard, M., You, D., Ranchoux, G., Bonnefon, J., Bachet, B. and Riot, G. (2012). "Simulations of corrosion product transfer with the OSCAR V1.2 code", *Proceedings of the Nuclear Plant Chemistry Conference 2012*, 24-28/09/12, Paris (France).

Eimecke, R. and Anthoni, S. (1988). "Ensemble de Mesures et d'Etude de la Contamination des Circuits", *Proceedings of the 7th International Conference on Radiation Shielding*, 12-16 September 1988, Bournemouth (GB), Vol. 1, p.103-113, UKAEA & OECD, Winfrith.

Harding, J.H. (1996). "Modelling the effect of zinc addition on the uptake of cobalt by oxide films in PWRs", *Proceedings of the International Conference on Water Chemistry of Nuclear Reactor System 7*, Bournemouth, 13-17 October 1996.

Lister, D.H. (1992). "Activity transport and corrosion processes in PWRs", *Proceedings of the International Conference on the Water Chemistry of Nuclear Reactor System 6*, 12-15/10/92, Bournemouth (GB), Vol. 2 49-60.

Parkhurst, D.L. and Appelo, C.A.J. (1999). "User's guide to PHREEQC (version 2) - A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations", *Report 99-4259*, US Geological Survey, Denver, Colorado.

Plancque, G., You, D., Blanchard, E., Mertens, V. and Lamouroux, C. (2011). "Role of chemistry in the phenomena occurring in nuclear power plants circuits", *Proceedings of the International Congress on Advances in Nuclear power Plants*, ICAPP, 2-5 May 2011, Nice (France).

Tigeras, A., Dacquait, F., Viricel, L., Segura, J.C., Guinard, L., Bretelle, J.L. and Rocher, A. (2008). "Complete Analyse of Zinc injection impact at BUGEY 2&4", *Proceedings of the International Conference on Water Chemistry of Nuclear Reactors Systems*, 15-18/09/08, Berlin (Germany), 1-32.