# Characterization of contamination : EMECC campaign at Sizewell B and comparison with French PWRs

Luc Guinard, Chris Bates, Gavin Lancaster, Frédéric Dacquait

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Luc Guinard, Chris Bates, Gavin Lancaster, Frédéric Dacquait. Characterization of contamination : EMECC campaign at Sizewell B and comparison with French PWRs. NPC 2008 - International Conference on Water Chemistry of Nuclear Reactors Systems, Sep 2008, Berlin, Germany. cea-04474046

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# Characterization of contamination : EMECC campaign at Sizewell B and comparison with French PWRs.

L. Guinard¹, C. Bates², G. Lancaster², F. Dacquait³

¹EDF SEPTEN, ²British Energy, ³CEA/DEN,
EDF SEPTEN, 12-14 avenue Dutrievoz, 69628 Villeurbanne, France

E-mail: luc.guinard@edf.fr

## Abstract

The reduction of collective dose is an important objective for all nuclear plant operators. One of the support for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs. EDF performs consequently gamma spectrometry measurements with CEA and his EMECC system, with more than 200 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators.

A recent collaboration between EDF and British Energy resulted in measurements during Refueling Outage 8 at Sizewell B, a PWR with excellent collective dosimetry. The paper presents the results in term of deposited activities and dose rates in RCS and CVCS, and compares with French PWRs, and especially with Saint-Laurent B1. If the dose rates are very comparable, the collective dosimetry is slightly lower for Sizewell B.

First explanations are searched for the established differences.

Lower ⁵⁸Co activity for Sizewell B is probably due to the good manufacturing of alloy 690 steam generator tubing, higher ⁶⁰Co activity is probably linked with the use of alloy 718 grids, not totally removed after 8 cycles.

The origin of difference in collective dosimetry should be less time spent in dosing outage operations, even if the total time spent in controlled area is rather higher in Sizewell B. An accurate comparison for specific chosen outage operations is in progress. Another explanation should be differences in contamination on auxiliary systems, or differences in volume activities. To explore further these hypothesis, complementary measurements are planned by BE and EDF.

All these comparisons will give new elements to BE and EDF to improve the behaviour of their own plants.

## 1. INTRODUCTION

The reduction of collective dose is an important objective for all nuclear plant operators. One of the support for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs. EDF performs consequently gamma spectrometry measurements with CEA and his EMECC system [1], with more than 200 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators. The comparison on low level contamination plants give elements to improve the behaviour of the plants. Consequently British Energy and EDF collaborated recently for measurements during Refueling Outage at Sizewell B.

## 2. EMECC CAMPAIGN AT SIZEWELL B

### 2.1 Plant measurements

Sizewell B is a Westinghouse 4-loops PWR with alloy 690TT tubes steam generators (SG). This unique British PWR is characterized by very low corrosion product releases and radiation fields [2]. In order to compare the contamination level of Sizewell B to that of

French PWRs, an EMECC campaign was performed during the refueling shutdown at the end of cycle 8.

The reactor coolant chemistry is boron-lithium coordinated chemistry with a target pH₃₀₀°C of 7.2. As a difference with French use, lithium can be over 2.2 mg/kg, till 3.5 mg/kg. The H₂ target concentration ranges between 30 and 45 cm³/kg, slightly higher than French range (25 - 35 cm³/kg). Cycle 8 lasted 475 EFPD, with the various steps of shutdown presented in figure 1.

<figure><img src="image_1.png" /><figcaption>Figure 1. Cold shutdown procedure - Sizewell B RF08</figcaption></figure>
# Characterization of contamination : EMECC campaign at Sizewell B and comparison with French PWRs.

L. Guinard¹, C. Bates², G. Lancaster², F. Dacquait³

¹EDF SEPTEN, ²British Energy, ³CEA/DEN,
EDF SEPTEN, 12-14 avenue Dutrievoz, 69628 Villeurbanne, France

E-mail: luc.guinard@edf.fr

## Abstract

The reduction of collective dose is an important objective for all nuclear plant operators. One of the support for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs. EDF performs consequently gamma spectrometry measurements with CEA and his EMECC system, with more than 200 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators.

A recent collaboration between EDF and British Energy resulted in measurements during Refueling Outage 8 at Sizewell B, a PWR with excellent collective dosimetry. The paper presents the results in term of deposited activities and dose rates in RCS and CVCS, and compares with French PWRs, and especially with Saint-Laurent B1. If the dose rates are very comparable, the collective dosimetry is slightly lower for Sizewell B.

First explanations are searched for the established differences.

Lower ⁵⁸Co activity for Sizewell B is probably due to the good manufacturing of alloy 690 steam generator tubing, higher ⁶⁰Co activity is probably linked with the use of alloy 718 grids, not totally removed after 8 cycles.

The origin of difference in collective dosimetry should be less time spent in dosing outage operations, even if the total time spent in controlled area is rather higher in Sizewell B. An accurate comparison for specific chosen outage operations is in progress. Another explanation should be differences in contamination on auxiliary systems, or differences in volume activities. To explore further these hypothesis, complementary measurements are planned by BE and EDF.

All these comparisons will give new elements to BE and EDF to improve the behaviour of their own plants.

## 1. INTRODUCTION

The reduction of collective dose is an important objective for all nuclear plant operators. One of the support for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs. EDF performs consequently gamma spectrometry measurements with CEA and his EMECC system [1], with more than 200 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators. The comparison on low level contamination plants give elements to improve the behaviour of the plants. Consequently British Energy and EDF collaborated recently for measurements during Refueling Outage at Sizewell B.

## 2. EMECC CAMPAIGN AT SIZEWELL B

### 2.1 Plant measurements

Sizewell B is a Westinghouse 4-loops PWR with alloy 690TT tubes steam generators (SG). This unique British PWR is characterized by very low corrosion product releases and radiation fields [2]. In order to compare the contamination level of Sizewell B to that of

French PWRs, an EMECC campaign was performed during the refueling shutdown at the end of cycle 8.

The reactor coolant chemistry is boron-lithium coordinated chemistry with a target pH₃₀₀°C of 7.2. As a difference with French use, lithium can be over 2.2 mg/kg, till 3.5 mg/kg. The H₂ target concentration ranges between 30 and 45 cm³/kg, slightly higher than French range (25 - 35 cm³/kg). Cycle 8 lasted 475 EFPD, with the various steps of shutdown presented in figure 1.

<figure><img src="image_2.png" /><figcaption>Figure 1. Cold shutdown procedure - Sizewell B RF08</figcaption></figure>
All the results will be compared with measurements performed at Saint-Laurent B1 during the refueling shutdown at the end of cycle 20. Indeed, Saint Laurent B1 is a Framatome 3-loops PWR with alloy 690TT tubes SG and equivalent duration of operation since SG replacement (performed after cycle 11).

## 2.2. Deposited activities

The deposited activities are presented in figure 2 for ⁵⁸Co in RCS, figure 3 for ⁶⁰Co in RCS, figure 4 for CVCS letdown pipe and figure 5 for letdown heat exchanger.

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /><figcaption>Figure 2. ⁵⁸Co RCS surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

⁵⁸Co and ⁶⁰Co contribute for more than 90% of the RCS and CVCS letdown pipe dose rates. The hot side of SG tubing is less contaminated than the cold side, either for ⁵⁸Co or ⁶⁰Co. The only main other nuclide for dose rate contribution is ¹¹⁰mAg for CVCS letdown heat exchanger (about 7%).

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>Figure 3. ⁶⁰Co RCS surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Figure 4. CVCS letdown pipe surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>
All the results will be compared with measurements performed at Saint-Laurent B1 during the refueling shutdown at the end of cycle 20. Indeed, Saint Laurent B1 is a Framatome 3-loops PWR with alloy 690TT tubes SG and equivalent duration of operation since SG replacement (performed after cycle 11).

## 2.2. Deposited activities

The deposited activities are presented in figure 2 for ⁵⁸Co in RCS, figure 3 for ⁶⁰Co in RCS, figure 4 for CVCS letdown pipe and figure 5 for letdown heat exchanger.

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>Figure 2. ⁵⁸Co RCS surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

⁵⁸Co and ⁶⁰Co contribute for more than 90% of the RCS and CVCS letdown pipe dose rates. The hot side of SG tubing is less contaminated than the cold side, either for ⁵⁸Co or ⁶⁰Co. The only main other nuclide for dose rate contribution is ¹¹⁰mAg for CVCS letdown heat exchanger (about 7%).

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>Figure 3. ⁶⁰Co RCS surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Figure 4. CVCS letdown pipe surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>
The comparison with St-Laurent B1 shows that the ⁵⁸Co surface activities are practically identical, as the ⁶⁰Co surface activities on hot legs. The ⁶⁰Co surface activities on crossover legs and SG tubing is higher in Sizewell B.

The letdown pipe is more contaminated in SIZB08 by the 2 main contributors (⁵⁸Co and ⁶⁰Co). Inversely, the letdown heat exchanger is more contaminated in SLB120 by the 3 main contributors (⁵⁸Co, ⁶⁰Co and ¹¹⁰mAg).

<figure><img src="image_9.png" /><figcaption>Figure 5. Letdown heat exchanger surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

### 2.3. Dose rates

<figure><img src="image_10.png" /><figcaption>Figure 6. Primary piping and SG tube bundle: CEA index</figcaption></figure>

Dose rate measurements were performed around the RCS for estimating CEA index (see figure 6 and table 1). The contribution of ⁵⁸Co and ⁶⁰Co is higher than 90% : 70% to 85% for ⁶⁰Co, 10% to 20% for ⁵⁸Co.

For CVCS, dose rate measurements are presented in table 2. For letdown pipe, the ⁵⁸Co contribution is higher : 30% compared with 60% for ⁶⁰Co due to the thinner pipe thickness. ⁶⁰Co is the major contributor to the dose rates around the letdown heat exchanger (75%), with ¹¹⁰mAg and ⁵⁸Co (about 7% each).

<table><caption>Table 1. Dose rates around primary system (CEA index - mSv/h) – Comparison Sizewell B / Saint-Laurent B1.</caption><thead><tr><th></th><th>SIZB08</th><th>SLB120</th></tr></thead><tbody><tr><td>Primary piping</td><td>0.19</td><td>0.18</td></tr><tr><td>SG tube bundle</td><td>0.10</td><td>0.08</td></tr></tbody></table>

<table><caption>Table 2. Dose rates at CVCS (mSv/h) – Comparison Sizewell B / Saint-Laurent B1.</caption><thead><tr><th></th><th>SIZB08</th><th>SLB120</th></tr></thead><tbody><tr><td>Letdown pipe</td><td>2.0</td><td>0.8</td></tr><tr><td>Letdown heat exchanger</td><td>0.15</td><td>2.3</td></tr></tbody></table>

The comparison with St-Laurent B1 for RCS shows similar dose rates whereas ⁶⁰Co surface activities are higher in SIZB08. Sizewell has the benefit of thicker component walls (e.g. SG shell thickness: 9.7 cm in SIZB compared with 8.5 cm in SLB1; hot leg thickness: 8.3 cm in SIZB compared with 6.9 cm in SLB1).

For CVCS letdown pipe, the dose rate are higher at SIZB08, due to higher surface activities and thinner walls. Inversely for letdown heat exchanger, the dose rate are lower in SIZB08, due to high ¹¹⁰mAg contamination in SLB120.

### 2.4. Volume activities

Figure 7 compares the ⁵⁸Co and ⁶⁰Co volume activities (including soluble and insoluble parts) for Sizewell B08 and Saint-Laurent B120. Excepting the two first operating months, the volume activities are 6 to 8 times lower in Sizewell B.

<figure><img src="image_11.png" /><figcaption>Figure 7. ⁵⁸Co and ⁶⁰Co volume activities – Comparison Sizewell B08 / Saint-Laurent B120.</figcaption></figure>

## 3. COLLECTIVE DOSIMETRY

The comparison between Sizewell B and St-Laurent B1 (see figure 8) indicates that Sizewell B has slightly lower collective dosimetry. However, St Laurent B1 performed a significant improvement for the last decade, due to efficient ALARA plans.

The average values for N4 units are very similar with Sizewell ones. N4 units have also significantly lower dose rate index than St-Laurent B1, which has the same trends than Sizewell B.

It can therefore be concluded that if the dose rates are very comparable (Sizewell B and St-Laurent B1), the collective dosimetry is slightly lower for Sizewell B. French units have similar collective dosimetry to Sizewell B one only with lower dose rates.
The comparison with St-Laurent B1 shows that the ⁵⁸Co surface activities are practically identical, as the ⁶⁰Co surface activities on hot legs. The ⁶⁰Co surface activities on crossover legs and SG tubing is higher in Sizewell B.

The letdown pipe is more contaminated in SIZB08 by the 2 main contributors (⁵⁸Co and ⁶⁰Co). Inversely, the letdown heat exchanger is more contaminated in SLB120 by the 3 main contributors (⁵⁸Co, ⁶⁰Co and ¹¹⁰mAg).

<figure><img src="image_10.png" /><figcaption>Figure 5. Letdown heat exchanger surface activities – Comparison Sizewell B / Saint-Laurent B1.</figcaption></figure>

## 2.3. Dose rates

<figure><img src="image_11.png" /><figcaption>Figure 6. Primary piping and SG tube bundle: CEA index</figcaption></figure>

Dose rate measurements were performed around the RCS for estimating CEA index (see figure 6 and table 1). The contribution of ⁵⁸Co and ⁶⁰Co is higher than 90% : 70% to 85% for ⁶⁰Co, 10% to 20% for ⁵⁸Co.

For CVCS, dose rate measurements are presented in table 2. For letdown pipe, the ⁵⁸Co contribution is higher : 30% compared with 60% for ⁶⁰Co due to the thinner pipe thickness. ⁶⁰Co is the major contributor to the dose rates around the letdown heat exchanger (75%), with ¹¹⁰mAg and ⁵⁸Co (about 7% each).

<table><caption>Table 1. Dose rates around primary system (CEA index - mSv/h) – Comparison Sizewell B / Saint-Laurent B1.</caption><thead><tr><th></th><th>SIZB08</th><th>SLB120</th></tr></thead><tbody><tr><td>Primary piping</td><td>0.19</td><td>0.18</td></tr><tr><td>SG tube bundle</td><td>0.10</td><td>0.08</td></tr></tbody></table>

<table><caption>Table 2. Dose rates at CVCS (mSv/h) – Comparison Sizewell B / Saint-Laurent B1.</caption><thead><tr><th></th><th>SIZB08</th><th>SLB120</th></tr></thead><tbody><tr><td>Letdown pipe</td><td>2.0</td><td>0.8</td></tr><tr><td>Letdown heat exchanger</td><td>0.15</td><td>2.3</td></tr></tbody></table>

The comparison with St-Laurent B1 for RCS shows similar dose rates whereas ⁶⁰Co surface activities are higher in SIZB08. Sizewell has the benefit of thicker component walls (e.g. SG shell thickness: 9.7 cm in SIZB compared with 8.5 cm in SLB1; hot leg thickness: 8.3 cm in SIZB compared with 6.9 cm in SLB1).

For CVCS letdown pipe, the dose rate are higher at SIZB08, due to higher surface activities and thinner walls. Inversely for letdown heat exchanger, the dose rate are lower in SIZB08, due to high ¹¹⁰mAg contamination in SLB120.

## 2.4. Volume activities

Figure 7 compares the ⁵⁸Co and ⁶⁰Co volume activities (including soluble and insoluble parts) for Sizewell B08 and Saint-Laurent B120. Excepting the two first operating months, the volume activities are 6 to 8 times lower in Sizewell B.

<figure><img src="image_12.png" /><figcaption>Figure 7. ⁵⁸Co and ⁶⁰Co volume activities – Comparison Sizewell B08 / Saint-Laurent B120.</figcaption></figure>

## 3. COLLECTIVE DOSIMETRY

The comparison between Sizewell B and St-Laurent B1 (see figure 8) indicates that Sizewell B has slightly lower collective dosimetry. However, St Laurent B1 performed a significant improvement for the last decade, due to efficient ALARA plans.

The average values for N4 units are very similar with Sizewell ones. N4 units have also significantly lower dose rate index than St-Laurent B1, which has the same trends than Sizewell B.

It can therefore be concluded that if the dose rates are very comparable (Sizewell B and St-Laurent B1), the collective dosimetry is slightly lower for Sizewell B. French units have similar collective dosimetry to Sizewell B one only with lower dose rates.
<figure><img src="image_12.png" /><figcaption>Figure 8. Comparison of collective dosimetry for Sizewell B, St-Laurent B1 and N4 units.</figcaption></figure>

## 4. DISCUSSION

The evidenced differences between Sizewell and Saint-Laurent are now to be discussed, to find explanations and ways of improvement.

### 4.1. *Design*

The potential reasons for higher ⁶⁰Co contamination in SIZB08 are reviewed :

- It should not be the SG tubing Co content, because it is very low (< 150 ppm) either in SIZB and SLB1.

- The influence of stellites is also not probable, because there is stellites reduction in CVCS valves in SIZB, not in SLB1.

- Inconel 718 grids could be the cause : for the first cycle in SIZB, all assemblies were equipped with Inconel 718 grids. A major part of them has been replaced, but there were still 13 assemblies equipped with Inconel 718 grids during cycle 8 (and 0 for SLB1). These grids have a specified maximum Co level of 400 ppm. Even if the majority have been now removed, their initial use can contribute to higher ⁶⁰Co contamination for many cycles because of ⁶⁰Co radioactive half-life (5.3 y).

Nevertheless, this cause is not proved. Inconel 718 grids (52% of Ni) should also increase ⁵⁸Co contamination, and this phenomenon is not obvious.

Both units have in common low ⁵⁸Co surface and volume activities several cycles after commissioning or SGR. One cause of this low ⁵⁸Co contamination level can be the very low corrosion release rate of alloy 690 SG tubing, due to improved manufacturing process.

### 4.2. *Operation*

There are no obvious difference in operating parameters between Sizewell and Saint-Laurent. The main differences are the longer cycle and the higher lithium content at beginning of cycle for Sizewell, but these parameters are not known for changing significantly the contamination [3].

Another cause for the low ⁵⁸Co surface and volume activities several cycles after commissioning or SGR should be Hot Functional Test (HFT) passivation procedure. However, there has been no passivation

procedure in SLB1. As ⁵⁸Co peaks is below 10 GBq/t 6 cycles after SIZB commissioning and 8 cycles after SLB1 SGR, it indicates probably that a modified passivation procedure with a complete water purification stage like in SIZEWELL-B should lower contamination level more quickly.

Last, we can note that volume activities are quite different, with lower values for SIZB, whereas similar volume activities during shutdowns and similar surface activities. For explaining such differences, maybe without impact on contamination, some exchanges between EDF and BE are in progress.

### 4.3. *Other causes*

An interesting indicator could be the time spent in controlled area. It is surprisingly higher for Sizewell B outages (about 80 000 h) than for French units outages (about 40 000 h). At first analysis, it could seem contradictory with “logical” and international trends [3] : the reduction of time is one of the main contributors for RP improvement. This data amplify the difference between Sizewell B and St-Laurent B1 : with similar dose rates and more time spent in controlled area, the collective dosimetry is lower for Sizewell B.

This analysis has consequently to be completed, by examining the differences in organization. It appears firstly that people work less “alone” during Sizewell B outages, with almost systematically one Health Physician together with each operator. This organization has two direct consequences : it can improve the working conditions and it increases “artificially” the time spent in controlled area. Another possible difference is less time in dosing outage operations, as for instance less work for SG inspections.

Other potential causes of differences have to be evaluated :

- differences in contamination on auxiliary systems, even if first results on CVCS (See figure 4 and 5) are not conclusive.

- differences in volume activities : could higher activities in French reactors have an indirect impact on contamination ? (it is well known that there is no direct impact, as more than 90% of dose rates are due to surface activities).

## 5. PERSPECTIVES

To explore further these hypothesis, complementary exchanges are in progress between BE and EDF. It should include measurements on auxiliary systems, accurate comparison for chosen outage operations and further investigations on differences in volume activities.

All these comparisons will give new elements to BE and EDF to improve the behaviour of their own plants.
<figure><img src="image_13.png" /><figcaption>Figure 8. Comparison of collective dosimetry for Sizewell B, St-Laurent B1 and N4 units.</figcaption></figure>

## 4. DISCUSSION

The evidenced differences between Sizewell and Saint-Laurent are now to be discussed, to find explanations and ways of improvement.

### 4.1. *Design*

The potential reasons for higher ⁶⁰Co contamination in SIZB08 are reviewed :

- It should not be the SG tubing Co content, because it is very low (< 150 ppm) either in SIZB and SLB1.

- The influence of stellites is also not probable, because there is stellites reduction in CVCS valves in SIZB, not in SLB1.

- Inconel 718 grids could be the cause : for the first cycle in SIZB, all assemblies were equipped with Inconel 718 grids. A major part of them has been replaced, but there were still 13 assemblies equipped with Inconel 718 grids during cycle 8 (and 0 for SLB1). These grids have a specified maximum Co level of 400 ppm. Even if the majority have been now removed, their initial use can contribute to higher ⁶⁰Co contamination for many cycles because of ⁶⁰Co radioactive half-life (5.3 y).

Nevertheless, this cause is not proved. Inconel 718 grids (52% of Ni) should also increase ⁵⁸Co contamination, and this phenomenon is not obvious.

Both units have in common low ⁵⁸Co surface and volume activities several cycles after commissioning or SGR. One cause of this low ⁵⁸Co contamination level can be the very low corrosion release rate of alloy 690 SG tubing, due to improved manufacturing process.

### 4.2. *Operation*

There are no obvious difference in operating parameters between Sizewell and Saint-Laurent. The main differences are the longer cycle and the higher lithium content at beginning of cycle for Sizewell, but these parameters are not known for changing significantly the contamination [3].

Another cause for the low ⁵⁸Co surface and volume activities several cycles after commissioning or SGR should be Hot Functional Test (HFT) passivation procedure. However, there has been no passivation

procedure in SLB1. As ⁵⁸Co peaks is below 10 GBq/t 6 cycles after SIZB commissioning and 8 cycles after SLB1 SGR, it indicates probably that a modified passivation procedure with a complete water purification stage like in SIZEWELL-B should lower contamination level more quickly.

Last, we can note that volume activities are quite different, with lower values for SIZB, whereas similar volume activities during shutdowns and similar surface activities. For explaining such differences, maybe without impact on contamination, some exchanges between EDF and BE are in progress.

### 4.3. *Other causes*

An interesting indicator could be the time spent in controlled area. It is surprisingly higher for Sizewell B outages (about 80 000 h) than for French units outages (about 40 000 h). At first analysis, it could seem contradictory with “logical” and international trends [3] : the reduction of time is one of the main contributors for RP improvement. This data amplify the difference between Sizewell B and St-Laurent B1 : with similar dose rates and more time spent in controlled area, the collective dosimetry is lower for Sizewell B.

This analysis has consequently to be completed, by examining the differences in organization. It appears firstly that people work less “alone” during Sizewell B outages, with almost systematically one Health Physician together with each operator. This organization has two direct consequences : it can improve the working conditions and it increases “artificially” the time spent in controlled area. Another possible difference is less time in dosing outage operations, as for instance less work for SG inspections.

Other potential causes of differences have to be evaluated :

- differences in contamination on auxiliary systems, even if first results on CVCS (See figure 4 and 5) are not conclusive.

- differences in volume activities : could higher activities in French reactors have an indirect impact on contamination ? (it is well known that there is no direct impact, as more than 90% of dose rates are due to surface activities).

## 5. PERSPECTIVES

To explore further these hypothesis, complementary exchanges are in progress between BE and EDF. It should include measurements on auxiliary systems, accurate comparison for chosen outage operations and further investigations on differences in volume activities.

All these comparisons will give new elements to BE and EDF to improve the behaviour of their own plants.
6. REFERENCES

[1] R. EIMECKE, S. ANTHONI. Ensemble de Mesure et d'Etude de la Contamination des Circuits (EMECC). 7th International Conference on Radiation Shielding. Bournemouth, England, 12-15 September 1988.

[2] J.C. BATES, K. GARBETT, K. HINDS, G.A. LANCASTER, M.A. MANTELL, G.A. RENN. Development of Corrosion Product Behaviour and Radiation Fields at the Sizewell B PWR from 1995 to 2008. VGB "International Conference on Water Chemistry of Nuclear Reactor Systems". Berlin, Germany, 14-18 September 2008.

[3] L. GUINARD, F. CATTANT, S. TAUNIER, J.L. BRETELLE, A. ROCHER, B. JEANNIN. General overview of the evolution of international collective radiation exposure and associated good practices. VGB "International Conference on Water Chemistry of Nuclear Reactor Systems". Berlin, Germany, 14-18 September 2008.
6. REFERENCES

[1] R. EIMECKE, S. ANTHONI. Ensemble de Mesure et d'Etude de la Contamination des Circuits (EMECC). 7th International Conference on Radiation Shielding. Bournemouth, England, 12-15 September 1988.

[2] J.C. BATES, K. GARBETT, K. HINDS, G.A. LANCASTER, M.A. MANTELL, G.A. RENN. Development of Corrosion Product Behaviour and Radiation Fields at the Sizewell B PWR from 1995 to 2008. VGB "International Conference on Water Chemistry of Nuclear Reactor Systems". Berlin, Germany, 14-18 September 2008.

[3] L. GUINARD, F. CATTANT, S. TAUNIER, J.L. BRETELLE, A. ROCHER, B. JEANNIN. General overview of the evolution of international collective radiation exposure and associated good practices. VGB "International Conference on Water Chemistry of Nuclear Reactor Systems". Berlin, Germany, 14-18 September 2008.