Benoît Habert

Frédéric Dacquait

Raphaël Lecocq

Kim Schildermans

Contamination Simulation of DOEL-4 PWR Using The OSCAR V1.2 Code and Parametrical Studies During Cycles or Cold Shutdowns

Keywords: contamination transfer, activated corrosion products, OSCAR V1.2, DOEL-4

The purpose of the OSCAR code, developed by the CEA in cooperation with EDF and AREVA NP, is to predict the contamination of the PWR primary system. The OSCAR code allows researchers to analyze corrosion products and fission products behavior and to calculate the activity in the fluid and the surface activity in the primary system. Nowadays, the OSCAR code is considered to be not only a tool for numerical simulations and predictions but also one that might combine and organize all new knowledge useful to progress on contamination caused by Activated Corrosion Products (ACPs). The OSCAR V1.2 code is used for ACPs simulation studies of DOEL-4 reactor. The 22 first cycles have been simulated and compared with measurements [1] of surface activities on the loops. Since, this simulation is the reference of DOEL-4 parametrical studies done with OSCAR V1.2. The effect on contamination by ACPs of a 4-month operation at 50% power during a cycle will be introduced. The results will be focused on volume and surface activities during the cycle and the following shutdown. Then several studies on mid-cycle shutdowns of a given length of time or with startup criteria on 58 Co volume activity will be presented. Last, results of parametrical studies performed on early oxygenation during cold shutdown will be given.

Introduction

The purpose of the OSCAR code, developed by the CEA in cooperation with EDF and AREVA NP, is to predict the contamination of the PWR primary system. The OSCAR code allows researchers to analyze corrosion products and fission products behavior and to calculate the activity in the fluid and the surface activity in the primary system. Nowadays, the OSCAR code is considered to be not only a tool for numerical simulations and predictions but also one that might combine and organize all new knowledge useful to progress on contamination caused by Activated Corrosion Products (ACPs). This article presents the results of the simulations of ACPs transfers using the OSCAR code V1.2 [START_REF] Dacquait | Simulations of corrosion product transfer with the OSCAR V1.2 code[END_REF]. The goals of these simulations are to demonstrate the ability of the OSCAR code to reproduce the ACPs contamination transfer of a given reactor (DOEL-4) by using precise operation data. Parametrical studies simulations are of particular interest because of the huge difficulty to carry out them during the operation. We will present here a selection of parametrical studies simulations, first the effect on contamination by ACPs of a 4-month operation at 50% power during a cycle will be introduced. The results will be focused on volume and surface activities during the cycle and the following shutdown. Then several studies on mid-cycle shutdowns of a given length of time or with startup criteria on 58 Co volume activity will be presented. Last, results of parametrical studies performed on early oxygenation during cold shutdown will be given.

Contamination simulation of the 22 first cycles of the DOEL-4 reactor

DOEL-4 is a 3-loops PWR equipped with alloy 690 tubed steam generators since the steam generator replacement at cycle 11. The structure of the DOEL-4 primary circuit has been modeled 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, refueling, steam generator replacement…) of the 22 first cycles have been averaged to obtain a one day step simulation. As a matter of comparison, we have used surface activities measurements coming from EMECC campaigns [START_REF] Eimecke | Ensemble de Mesure et d'Etude de la Contamination des Circuits[END_REF] carried out during some shutdowns and volume activities measured during the operation. A good agreement between simulation and measurements of the deposited activities of 58 Co and 60 Co can be observed in Figure 1. Nevertheless, the 58 Co contamination during the first cycle seems to be overestimated. It comes from an excessive release of corrosion products during the first cycle. This modelled release could have been reduced, but we decided not to do so because of the lack of measurement for the first cycle and the weak influence of the first cycle release on the contamination simulation at the cycle that can be compared with measurements. Moreover, note that the orders of magnitude being sought, we did not try to optimize the results by an advanced calibration.

Contamination simulation during a typical cold shutdown of the DOEL-4 reactor

The modelling of the cold shutdown with the OSCAR code [START_REF] Dacquait | Simulations of corrosion product transfer with the OSCAR V1.2 code[END_REF] allowed reproducing the 58 Co volume activity peak observed in the primary circuit. This peak is explained by a fast dissolution of nickel simple phases deposited on the fuel cladding leading to the dissolution of 58 Co formed by activation of 58 Ni.

The dissolution of the 58 Co is modelled through a driving mechanism linked to the nickel phase it is trapped into. So the amount of 58 Co released during the cold shutdown is rigorously determined by the amount of nickel simple phases deposited on the fuel cladding before the shutdown.

The operation data of a typical cold shutdown are drawing in Figure 2. Note that the concentrations of oxygen and hydrogen are fixed to the given values. The variation of the 58 Co volume activity is presented in Figure 3. The peak value, 170 GBq/t, is overestimated (several tens of GBq/t measured) and is explained by a too large simulated mass of metal nickel deposited on the fuel cladding at the beginning of the shutdown (2 kg).

The composition of the Ni on the cladding is based on equilibrium calculation and doesn't take into account the kinetics of the phase changes; it might be that phase changes, which give metal Ni, are simulated though they actually never occur because of their low kinetic. Otherwise, no increase of APCs surface activities is observed on the primary loops, this agrees with the feedback. Despite the overestimation of the 58 Co volume activity peak, this modelling was used as a reference for parametrical studies that will be further presented.

Impact of a 50%-power operation

We have studied the impact of a 4-month operation at 50% power during a cycle. The operation data of the cycle have been replaced by typical ones (constant power, constant hydrogen concentration and smooth decrease of boron and lithium concentrations), this modelling is the reference for this study. The 50% power operation is simulated by a neutron activation divided by 2, a decrease of the temperature of the "hot" regions (the average temperature evolves from 302 °C to 293.7 °C; for the hot legs: from 321 °C to 304 °C; while for the cold legs it is stable at 283 °C). The concentrations of boron and lithium are increased during the drop of power; their concentrations are given in Figure 4. The 50% power operation period starts around 2 months after the beginning and ends 9 months before the end of the cycle. This study combines the effects of two phenomena:  the drop of power decreases the temperature (and also the equilibrium concentration) and the source term of the APCs contamination (neutron activation divided by 2),  the change of the chemical conditions influence the pHT which decreases slightly from 7.1 to 7.06 at the beginning of the 50% power period).

All the simulated volume and surface activities decrease during the 50% operation period; then they increase when power returns to its nominal value. At the end of the cycle, their values are close to the reference ones (see Figures 5 &6). According to the OSCAR simulation, a 50% power operation during 4 months has a slight influence during this period and few months after. Then 6 months after, the contamination levels are equivalent to those obtained with a nominal power operation. As consequence, if the extended period at 50% occurred less than 6 months prior to refueling outage, an influence on the shutdown release would be noticed.

Mid-cycle shutdown 5.1 14-day shutdown

The goal of this study is to determine the influence of mid-cycle shutdowns on the contamination levels according to the moment of the shutdown during the cycle. The shutdown was simulated at three moments of the cycle: 9, 6 and 3 months before the end of cycle. The shutdown modelling uses the same operation data than the typical cold shutdown. The restart was roughly modelled: the operation data linearly evolving from the shutdown values to the nominal ones in one day (see Figure 7). For the other regions of the loops (steam generators, crossover legs…) the variations of the surface activities are similar to the hot legs ones. A strong influence on the 58 Co contamination and a weak one for 60 Co are observed. This comes from the strong impact of the mid-cycle shutdown on the amount of nickel on the fuel cladding which strongly decreased. No increase in surface activities on the loops is observed during the mid-cycle shutdown. The cobalt peaks of the mid-cycle shutdowns are the highest when the shutdown is the closer to the end of the cycle. The end of cycle cold shutdown cobalt peaks decrease when the mid-cycle is close to the end of cycle. This is illustrated in Table 1 with the ratio of the 58 Co peaks for the mid-cycle shutdowns and the end of cycle cold shutdown divided by the value of the 58 Co reference peak at the end of cycle cold shutdown (without mid-cycle shutdown).

Table 1. Ratio of the 58 Co peaks compared with the reference cold shutdown peak.

The influence of the mid-cycle shutdown disappears at the beginning of the following cycle for the volume activities and during this cycle for the surface activities (see Figures 7 &8). 9 months 6 months 3 months Mid-cycle shutdown 29% 60% 85% Cold shutdown 68% 47% 20%

This behavior is similar to the one highlighted for unexpected shutdown with oxygenation during a cycle [START_REF] Dacquait | Corrosion product transfer in French PWRs during shutdown[END_REF] that showed an even more low 58 Co peak since the shutdown is close to the end of cycle.

Early restarts for mid-cycle shutdown

The influence of an early restart of the mid-cycle shutdown has been studied with two restart criteria: a 58 Co volume activity in the primary circuit of respectively 7 GBq/t and 50 GBq/t.

The reference case is the mid-cycle shutdown 6 months before the end of cycle for which the 58 Co volume activity at the restart is 0.5 MBq/t. For both cases, an increase of the 58 Co surface activities on the legs of the loops is observed (see Table2); while the contamination on the steam generator tubing surface is stable. There is also an increase of the 60

Early oxygenation during the cold shutdown

The influence of an early oxygenation during the cold shutdown has been modelled. The OSCAR code doesn't calculate the oxygen consumption, so the modelling of this consumption was made by a return to a reducing condition between the parasitical oxygenation and the main one.

The modelled oxygenation starts at a temperature of 180 °C, the primary circuit stays in an oxidant condition during one hour and then returns in the reducing condition of the reference case. For this study, the only changes compared to the reference are the concentrations in oxygen and hydrogen during the one-hour oxygenation.

A double peak of volume activities is observed for the 58 Co (see Figure 10); the first peak value is 54% of the peak without oxygenation and the second is 57%. The simulation of the deposited activities presents a huge increase for the 58 Co on the cold side of the SGs (+210%) at the end of the early oxygenation, whereas it stays stable on the hot side (+1%) and increases slightly on the legs (+5%). This increase is explained by the huge decrease of cobalt equilibrium concentrations at the return in a reducing condition. The cold side of the SGs is the loops region with the lowest cobalt equilibrium concentration, which explains the local massive precipitation; moreover, no release is observed from the SGs, thus the amount of 58 Co deposited activities on the SGs stays stable during the main oxygenation. Those results confirm that early oxygenations have to be avoided.

Conclusion

This present article demonstrates the ability of the OSCAR code V1.2 to reproduce the ACPs contamination transfer of the DOEL-4 reactor during 22 cycles. Then parametrical studies that are of particular interest for operators were presented. The simulation of a 50% power operation during 4 months reveals a slight influence on the contamination which disappears 6 months after the return to the nominal power. Thus a 50% power operation during the 6 last months of a cycle will have effects on the shutdown. Mid-cycle shutdown simulations show a strong impact during the rest of the cycle, it decreases the 58 Co contamination (volume and surface activities and peak of the end-ofcycle shutdown); the effects slowly vanish during the next cycle. Those beneficial effects can be wiped out when the restart for the mid-cycle shutdowns happens too early; it leads to an increase of the 58 Co surface activities on the loops. Finally, the simulation of an early oxygenation during the cold shutdown produces double cobalt peaks and induces a local precipitation on the cold side of the SGs at the end of the early oxygenation. It confirms the risk of ACPs precipitation when early oxygenations occur.

Figure 1 .

 1 Figure 1. Simulation of the 58 Co and 60 Co surface activities on the hot legs, crossover legs and the hot and cold sides of the SGs compared with EMECC measurements This simulation has proved the ability of the OSCAR code to simulate the contamination transfer of a reactor during a large number of cycles given the modelling with control volumes and the use of close to reality operation data.

Figure 2 .

 2 Figure 2. Operation data during a typical cold shutdown.

Figure 3 .

 3 Figure 3. Simulated 58 Co volume activity in the primary circuit during the cold shutdown.

Figure 4 .

 4 Figure 4. Boron and lithium concentrations for the reference (green) and for the cycle with a 50% power operation (blue)

Figure 5 .Figure 6 .

 56 Figure 5. Volume activities of 58 Co and 60 Co for the reference (green) and for the cycle with a 50% power operation (blue)

Figure 7 .

 7 Figure 7. Operation data during the 14-day shutdown. The simulation of the 58 Co and 60 Co volume and surface (for the hot legs) activities are presented in Figures 8 & 9 for the cycle with the mid-cycle shutdown and the following cycle.For the other regions of the loops (steam generators, crossover legs…) the variations of the surface activities are similar to the hot legs ones. A strong influence on the 58 Co contamination and a weak one for 60 Co are observed. This comes from the strong impact of the mid-cycle shutdown on the amount of nickel on the fuel cladding which strongly decreased. No increase in surface activities on the loops is observed during the mid-cycle shutdown. The cobalt peaks of the mid-cycle shutdowns are the highest when the shutdown is the closer to the end of the cycle. The end of cycle cold shutdown cobalt peaks decrease when the mid-cycle is close to the end of cycle. This is illustrated in Table1with the ratio of the

Figure 8 .

 8 Figure 8. 58 Co and 60 Co volume activities during 2 cycles, without shutdown (green) and with 14-day shutdown 9 months (blue), 6 months (pink) and 3 months (turquoise) before the end of the cycle.

Figure 9 .

 9 Figure 9. 58 Co and 60 Co surface activities on the hot legs during 2 cycles, without shutdown (green) and with 14-day shutdown 9 months (blue), 6 months (pink) and 3 months (turquoise) before the end of the cycle.

Figure 10 .

 10 Figure 10. Simulated 58 Co volume activity in the primary circuit during the cold shutdown for the early oxygenation case (in blue) and for the reference case (blue).

Table 2 . Increase in the 58 Co surface activities during the early restart mid-cycle shutdowns.

 2 Co surface activities, but it is almost negligible, the difference with the 58 Co is explained with the far lower amount of 60 Co released in the primary water during the shutdown.

			50 GBq/t		7 GBq/t
		Hot legs	Crossover legs	Hot legs	Crossover legs
	58 Co	+154%	+106%	+29%	+20%

NPC 2014 SAPPORO


Yannick Lucotte
email: yannick.lucotte@etu.univ-orleans.fr

Sylviane Guillaumont Jeanneney

Jean-Paul Pollin

Angela Mitrea

« Central Bank Independence and Budget Deficits in Developing Countries: New Evidence from Panel Data Analysis »

Keywords: Central bank independence, Budget balances, Developing countries, Panel data analysis JEL Codes: E58, H62

Au cours des vingt dernières années, de nombreux pays ont révisé profondément les statuts régissant le fonctionnement et les missions de leurs banques centrales afin de conférer à ces dernières une plus grande indépendance vis-à-vis du pouvoir politique. Cette évolution concerna plusieurs pays, aussi bien développés qu'en développement, et est conforme à la théorie de l'incohérence temporelle de la politique monétaire de Barro et Gordon, qui met en avant l'importance de l'indépendance de l'autorité monétaire pour l'acquisition d'une crédibilité anti-inflationniste. En outre, le statut de la banque centrale peut également affecter la conduite de la politique budgétaire. La littérature théorique montre en effet qu'une forte indépendance incite le gouvernement à davantage de discipline budgétaire, et inversement. Cependant, le peu d'études empiriques consacrées à cette question concernent essentiellement des pays développés et ont abouti à des résultats économétriques décevants. Afin de combler cette lacune, nous analysons la manière dont le degré d'indépendance de la banque centrale influence le niveau de déficit budgétaire pour un large échantillon de pays en développement sur la période 1995-2004, en nous appuyant sur deux indicateurs d'indépendance développés par la littérature. Les résultats des estimations indiquent une relation négative entre degré d'indépendance et niveau de déficit budgétaire.

Introduction

During the last two decades, many countries have deeply reformed their central banks' legislation in order to confer them greater independence and, to define clearly their primary objective: maintaining price stability. Indeed, it is often argued that a high degree of central bank independence (hereafter CBI) coupled with an explicit mandate that the central bank aim for price stability are essential for maintaining that stability. During 1989[START_REF] Cukierman | The economics of Central Banking[END_REF][START_REF] Cukierman | The economics of Central Banking[END_REF] shows that these legislative reforms concern 25 countries, both industrial and emerging or developing countries, particularly Latin American. According to [START_REF] Cukierman | Political Influence on the Central Bank: International Evidence[END_REF], these countries have increased the independence of their monetary authorities for various reasons (economic, political, and historical).

Why the central bank should be independent? The traditional origin of theoretical studies on CBI and the governor's degree of conservatism is the time-inconsistency problem of political choices [START_REF] Kydland | Rules Rather than Discretion: The Inconsistency of Optimal Plans[END_REF]. According to this concept of time-inconsistency, an ex ante optimal policy can prove no optimal ex post, the government reserved the right to "cheat" without respecting the announced policy. Applied to monetary policy (Barro andGordon [1983a, 1983b], Backus and Drifill [1985]), the direct consequence of the timeinconsistency problem is the loss of credibility of central banks and an inflationary bias of discretionary monetary policy. One of the solutions to this problem is to appoint a conservative central bank governor, in the sense that he places a greater weight on price stability than the government does [START_REF] Rogoff | The Optimal Degree of Commitment to an Intermediate Monetary Target[END_REF]. In practice, CBI could be a manner of appointing a conservative central banker. Furthermore, concerning this time-inconsistency problem, recent studies have suggested that CBI could allow the protection of monetary policy against partisan electoral cycles [START_REF] Alesina | Macroeconomics and Politics[END_REF][START_REF] Alesina | Political Cycles and the Macroeconomy[END_REF] and therefore not to divert the monetary policy from its primary objective. So the principal message of these theories is that government suffers from an inflationary bias and that, it is necessary to depoliticize monetary policy (i.e. increase the CBI) in order to fight more efficiently against inflation.

The idea that an independent central bank is associated with lower inflation was supported by an important empirical literature which suggests that average inflation is negatively related to the CBI degree2 . However, the majority of these empirical studies are done for OECD countries and, when developing countries are included in the sample, results are very weak and sensitive to the indicator of CBI used. Indeed, most empirical studies used an indicator based on central bank laws in place (de jure independence) but, a legal approach is not fit for developing countries. Cukierman, Webb and Neyapti (1992, pp. 361-363) argue that "the legal status of a central bank is only one of several elements that determine its actual independence. Many central banks laws are highly incomplete and leave a lot of room of interpretation. As a result, factors such as tradition or the personalities of the governor and other high officials of the bank at least partially shape the actual level of CBI. Even when the law is quite explicit, reality may be very different". Thus, according to Fuhrer (1997, p. 27), "legal CBI could be very different from actual CBI in countries where the practice of monetary policy deviates from the letter of the law. Measures of legal CBI should thus be viewed as (possibly noisy) indicators of underlying CBI". For this reason, [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] and [START_REF] Cukierman | Political Influence on the Central Bank: International Evidence[END_REF] have developed de facto indicators of CBI, more adequate than de jure indicators when studying the CBI in developing and emerging countries. So in this paper two complementary approaches to assess CBI are proposed: one legal with the [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] index (hereafter CWN), the most widely employed legal indicator of CBI in the empirical literature and, one behavioral with the turnover rate of central bank governors (hereafter TOR).

Moreover, the theoretical literature [START_REF] Masciandaro | Monetary Regimes and Fiscal Deficit: A Comparative Analysis[END_REF][START_REF] Castellani | Central Bank Independence and the Design of Fiscal Institutions[END_REF][START_REF] Montiel | Macroeconomics in Emerging Markets[END_REF] shows that CBI should affect the design of fiscal policy, i.e. a greater degree of independence influences the central government to fiscal discipline; inversely, a weak independence could influence the government to fiscal laxity. This view is associated with the question of sources of financing for government deficit. The adoption of an independent central bank deprives the government from inflation tax and so constitutes a strong signal for fiscal discipline. According to [START_REF] Mankiw | The Optimal Collection of Seigniorage: Theory and Evidence[END_REF], inflation is a source of revenue and must be considered as a part of the global budgetary policy. Indeed, as debt and interest rates are measured in nominal terms (i.e. the interest rates are not indexed on inflation rate), generating inflation depreciates the real value of intern public debt and interest payments. Masciandaro and Tabellini (1987, p. 133) conclude that "the crucial determinant of fiscal policy is the monetary regime, that is, the link between current deficits and future monetization".

However, despite the voluminous literature on CBI, the majority of empirical studies on CBI are focused on the relationship between CBI and inflation. There has been few positive analysis of the relationship between CBI and budget deficits. To the best of our knowledge, seven empirical studies have investigated the relationship between the CBI degree and the level of budget deficits3 . But, quantitative analysis (statistic/econometric strategy) of these studies are open to criticism and, results are ambiguous or even not statistically significant.

Besides, only [START_REF] Sikken | Budget deficits, monetization, and central-bank independence in developing countries[END_REF] have addressed this issue for developing countries.

Using three indicators of CBI (de jure and de facto) developed in the literature, these authors refute the theoretical results and, conclude that there is no relationship between CBI and the level of budget deficits during 1972-89 period on the sample of 30 developing countries.

Accordingly, the aim of this paper is to assess econometrically the influence of CBI on the level of government budget deficits in developing countries. The econometric analysis uses panel data and focuses on a large set of developing countries during 1995-2004 period. The results show a negative relationship between de facto CBI and government primary budget surplus.

The remainder of this paper is organized as follows. Section 2 defines the concept of CBI, while section 3 presents CBI measures used in this study. Section 4 introduces the econometric analysis and data. Section 5 provides and discusses results. The last section concludes and gives some policy implications derived from the empirical findings.

What is independence?

Generally speaking, independence means that, abstracting from exceptional circumstances, nobody can interfere in the decisions made by the central bank in the exercise of its functions or, reverse the course of its decisions [START_REF] Patat | L'ère des banques centrales[END_REF].

More precisely, CBI refers to three areas where the influence of government must be either excluded or drastically curtailed [START_REF] Hasse | The European Central Bank: Perspectives for the Further Development of the European Monetary System (Strategies and options for the future of Europe)[END_REF]: organic, functional and financial independence.

Organic independence relates to the conditions under which central bank executives are appointed, the term and the renewal of their mandates (in particular of the governor), as well as the composition of the central bank's governing bodies, i.e. if government representatives have (or not) the right to sit and vote within these authorities. However, [START_REF] Bassoni | Autonomie des banques centrales et performances macroéconomiques. Un réexamen[END_REF] underline that recent studies have focused on real term of governors' mandates (TOR) and, on the degree of synchronization between the mandates of central bank governor and of chief of executive power.

Functional independence (or operational independence) refers to the effective freedom the central bank enjoys, not only in the definition of objectives to pursue, but also in the conduct of monetary policy, which includes the choice of instruments. According to [START_REF] Henning | Currencies and Politics in the United States, Germany and Japan[END_REF], independence refers to the ability of the central bank to use the instruments of monetary control without instruction, guidance or interference from the government. Thus, some authors subdivide the functional independence and make a difference between: (i) goal independence, (ii) target independence and (iii) instrument independence. The difference between these three levels of independence is nevertheless subtle and so requires to be clarified, especially for the two first levels4 .

(i)

Goal independence imparts to the central bank to determine the monetary policy and exchange rate regime, or simply the monetary policy in the case of a floating exchange rate. More precisely, goal independence gives to the emission institute the authority to determine its primary objective among several objectives included in the central bank law or, less frequently, to determine its primary objective if the law doesn't clearly define the objectives.

(ii) Target independence, as the precedent form of independence, entrusts the monetary authority with the responsibility of determining the monetary policy and exchange rate regime, or simply the monetary policy if the exchange rate is floating. However, target independence differs from goal independence because the primary objective that the central bank must pursue through its monetary policy is clearly defined in the law. So, the central bank has an absolute autonomy in the choice of specific target (monetary base, interest rate, inflation rate) to pursue its legislative objective(s), such as price stability.

(iii) Instrument independence means that the government or the legislature defines the monetary policy and its objectives, in accordance with the central bank and the exchange rate regime. However, the monetary authority keeps sufficient autonomy to implement this policy using the appropriate instruments.

According to [START_REF] Debelle | How Independent Should a Central Bank Be?", Goals, Guidelines and Constraints Facing Monetary Policymakers[END_REF], a central bank should enjoy instrument independence but not goal independence [START_REF] Grilli | Estimations de fonctions de gains sur données de panel: endogénéité du capital humain et effets de la sélection[END_REF] call these two dimensions "political independence" and respectively "economic independence"). Indeed, goal independence is clearly the form of independence giving greater autonomy to a central bank.

But, [START_REF] Lybek | Central Bank Autonomy, Accountability, and Governance: Conceptual Framework[END_REF] and [START_REF] Blinder | Central Banking in Theory and Practice[END_REF] bring interrogation to the justification to give the central bank such authority because governors, who are not elected by citizens directly, should have the power to decide the short-term trade-off between inflation and unemployment. On the contrary, we think that the fight against inflation must be seen as an inestimable public good and not as the simple counterpart of unemployment, particularly in developing economies where inflation affects primarily poor and vulnerable populations.

Financial independence refers to the possibility (and to what extent) for a government to finance its expenditures by resorting directly or indirectly to advances and loans from central bank. Moreover, according to [START_REF] Bassoni | Autonomie des banques centrales et performances macroéconomiques. Un réexamen[END_REF] financial independence allows the assessment of the budgetary "breathing space" which central bank disposes, i.e. CBI vis-àvis its financial resources necessary to its functioning. This second aspect of financial independence can be described as budgetary independence5 .

The definition of CBI allows us to show the complexity and the pluri-dimensionality of this concept and so, the difficulty to measure this independence.

Measures of Central Bank Independence

The first and main challenge of empirical studies dealing with the relationship between CBI and inflation is to quantify CBI. Several measures of CBI have been proposed in the literature: de jure indexes [START_REF] Bade | Central Bank Laws and Monetary Policy[END_REF][START_REF] Bodart | Central Bank Independence and Monetary Policy Effectiveness: A Comparative Analysis[END_REF][START_REF] Grilli | Estimations de fonctions de gains sur données de panel: endogénéité du capital humain et effets de la sélection[END_REF][START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF][START_REF] Alesina | Central Bank Independence and Macroeconomic Performance: Some Comparative Evidence[END_REF][START_REF] Eijffinger | Central Bank Independence in Twelve Industrial Countries[END_REF][START_REF] Ilieva | Measures and Patterns of Central Bank Independence in Transition Economies[END_REF] and, de facto indexes [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF][START_REF] Cukierman | Political Influence on the Central Bank: International Evidence[END_REF].

But as previously mentioned, CBI is a multidimensional concept and so, defining and constructing a relevant index is arduous. The difficulty with measuring independence is reinforced by the fact that empirical results are very sensitive to the indicator of CBI used, especially when the sample of the study contains some "moderately independent" central banks. Indeed, even though these indicators are similar in general, in the sense that their common objective is to measure CBI, they provide quite different outcomes if we compare the rank of countries by degree of CBI for the same period. The rank correlation coefficients between four legal indexes of CBI calculated by [START_REF] Eijffinger | The political Economy of Central-Bank Independence[END_REF] confirm this result, with relatively low correlations. According to [START_REF] Mangano | Measuring Central Bank Independence: A Tale of Subjectivity and of its Consequences[END_REF], three explanations can be given for these diverging outcomes: As mentioned in the introduction, this study focuses on two CBI indicators: one de jure, with

CWN index and, one de facto, with TOR. Construction methodology, advantages and limits of these indexes are presented below.

De jure independence

The important number of empirical studies using CWN index can be explained by the fact that this index of legal independence is the most comprehensive. Certainly, and contrary to other CBI indexes, CWN index focuses on the four aspects of CBI outlined in section 2. Moreover, this index is "comprehensive in terms of its elements and is relatively easy to replicate since the authors provide a thorough guide to coding the various subcomponents" (Crowe and Meade, 2008, p. 765).

The CWN index is a weighted sum of 16 sub-items which are grouped into the following four categories (the number between brackets indicates the number of variables into each cluster): In comparison to alternative CBI measures developed in the literature that only permit yes/no decisions for each criterion, the major evolution brought by the CWN index is that it widens considerably the range of responses, in the sense that a score between 0 (smallest level of independence) and 1 (highest level of independence) is given to each of the 16 variables. For example, there are five possible ratings for the question concerning the term of the mandate: 1 (if the central bank governor serves > 8 year term), 0.75 (6-8 year term), 0.5 (5 year term), 0.25 (4 year term) or 0 (under 4 year term). Moreover, [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] include a weighting system in their indicator aiming to give a different weight to each component and so implicitly, a different weight to each of the four aspects of independence. The weighting system is the following: CEO (0.20 % of index), PF (0.15%), OBJ (0.15%) and, LL (0.50%).

This codification and weighting system certainly permits a more fine analysis and measure of CBI but gives also a more important place to arbitrary and subjectivity. Finally, the "overall index" for each central bank is obtained by calculating a weighted arithmetic average of variables6 .

De facto independence

The concept of actual independence includes many aspects, such as the turnover rate of central bankers, their personality and charisma and also the design of fiscal and monetary policies [START_REF] Radzyner | Central Bank Independence in Transition: Legislation and Reality in Central and Eastern Europe[END_REF]. To identify the differences between de jure and de facto CBI, [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] and [START_REF] Cukierman | Political Influence on the Central Bank: International Evidence[END_REF] use three nonlegal measures of CBI7 . This paper restricts the analysis of real CBI to TOR because many empirical studies have proven that TOR is a good proxy to assess actual CBI in particular for developing countries and, data are easily available (via notably central bank websites).

TOR is defined as the average term of office of central bankers. It is calculated by dividing the number of central bank governors during a given period by the number of years of this reference period. Thus, for example, a TOR equal to 0.5 means that there has been a change of governor every two years (0.5 change per year). So, this indicator takes into account the potential deviations from the law concerning the term of office of the central bank governor.

To prove the pertinence of this index as a proxy of actual CBI, [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] give the example of Argentina, where an informal tradition wants that the governor of Banco Central de la Republica Argentina resigns whenever there is a change of government, or even a new finance minister, even though the legal term of the central banker office is four years.

Consequently, during 1950-89, the real term of office of Argentina central bank governors is less than one year (TOR = 0.93). Through this example, we comprehend the intuition of this index: a high turnover of central bankers indicates a low level of independence because monetary authority executive directors are subject to electoral and political cycles which means they are under government's influence when conducting the monetary policy. The term of office of central bank governors is therefore a guarantee of CBI vis-à-vis political power, especially when it exceeds the average length of electoral cycle of a considered country. Thus, as in many countries the average length of this cycle is four years, [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] consider that a TOR superior to 0.25 is synonymous with low CBI. Nevertheless, [START_REF] Mas | Central Bank Independence -A Critical View from Developing Country Perspective[END_REF] expresses a limit about the use of this index as proxy of real CBI: a long term in office may also indicate a low level of independence, because a subservient governor can hold his position for a long period of time and survive to several governments despite his lack of independence.

Despite their apparent limits, these two CBI indexes are very used by the empirical literature.

So, in this study, we decide to retain these indicators to assess the influence of CBI on budget deficits in developing countries.

Econometric Strategy and Data

To estimate the influence of CBI on budget surpluses during the period of 1995-2004, we use a panel data analysis. The sample includes all developing countries for which we have the required data (see Appendix B).

The estimated equation is therefore

CGPBS 𝑖𝑡 = 𝛽 0 + β 1 CBI 𝑖 + β 2 LRGDP 𝑖𝑡 + β 3 GRGDP 𝑖𝑡 + β 4 URB 𝑖𝑡 + β 5 AGRI 𝑖𝑡 + β 6 ILLY 𝑖𝑡 + β 7 OPEN 𝑖𝑡 + γ 1 RD 𝑖 + γ 2 CU 𝑖 + μ it (1) μ it = 𝛼 𝑖 + 𝜀 𝑖𝑡
where i denotes the country and t denotes the time, α i is an unobserved country-specific effect, ε it is the error term, and the variables are defined as follows:

CGPBS it denotes the central government primary budget surplus (as a percentage of GDP),

CBI i is the central bank independence measured by the two subindexes of CBI previously described (CWN and TOR),

LRGDP it is the log of real per capita GDP, GRGDP it is the real GDP annual growth rate, URB it is the degree of urbanization, AGRI it is the share of agriculture in the GDP, ILLY it is the ratio of liquid liabilities of the financial system to GDP, OPEN it is the trade openness, RD i corresponds to regional dummies, CU i is a binary variable equal to 1 if the country i is a member of a currency union and 0 otherwise.

We are interested in the β 1 coefficient, which is the effect of CBI on primary budget surplus.

The main advantage of our econometric analysis compared to the previous empirical studies is the use of panel data technique to estimate the relationship between the degree of CBI and the budget deficit. However, for the period under consideration, the time variation of our CBI indicators is limited or even null for TOR. Thus, we cannot use fixed effects methodology because it removes the variables with not intra-individual variability, like in the case of CBI indexes and dummies8 . Concerning the random effects model, the generalized least squares (GLS) estimator is consistent and efficient only under the assumption that the explanatory variables are not correlated with specific effects. If this assumption is not verified, the GLS estimator is biased and inconsistent. According to [START_REF] Mundlak | On the Pooling of Time Series and Cross Section Data[END_REF], the probability of no correlation between individual specific effects and some explanatory variables is low. But, in the presence of time-invariant variables, the usual test of [START_REF] Hausman | Specification Test in Econometrics[END_REF] consisting in the comparison of the within and between estimators cannot be used because the test concerns only variables with intra-individual variability [START_REF] Sevestre | Econométrie des données de panel[END_REF].

To resolve this potential endogeneity bias specific to panel data econometrics, [START_REF] Hausman | Panel Data and Unobservable Individual Effects[END_REF] (hereafter HT) developed "an estimator that is, in essence, a hybrid of the fixed effects and generalized least squares (random effects) models" (Gardner, 1998, pp. 39-40).

This alternative methodology rests upon the method of instrumental variables but, offers the advantage of using internal instruments and so, doesn't require finding valid instruments outside the model. For that, HT makes a classification of explanatory variables according to their endogenous or exogenous character, i.e. correlated or not correlated with unit specific variables must be larger or equal than the number of Z2 variables (k1 ≥ g2). The principal limit of the strategy proposed by HT is that the decision on which variables are treated as exogenous/endogenous is not obvious and, HT suggest mainly using economic intuition 9 . In this paper, we assume that the variable of GDP per capita is endogenous, i.e. correlated with specific effects, and so we include this variable in X2. In fact, we can think that this variable is linked to unobservable characteristics of countries as for example the historical past, the dominant religion or the culture.

9 Besides economic intuition, [START_REF] Claessens | Empirical Evidence on the New International Aid Architecture[END_REF] rely on the insight of [START_REF] Baltagi | Fixed effects, random effects or Hausman-Taylor? A pretest estimator[END_REF] and develop a "formal test" to help researchers in their selection of the explanatory variables considered as endogenous. Their methodology consists in applying a Hausman test between fixed effects and HT models by instrumenting one variable at the time (from least to most exogenous on the basis of economic intuition), up to the point where the Hausman test suggests that the non-instrumented regression is more appropriate. So, variables instrumented can be considered as endogenous and the remaining explanatory variables exogenous vis-à-vis individual specific effects. But, this methodology cannot be used when the model contains time-invariant variables or dummy variables because these variables are eliminated by the within transformation.

The HT estimator was firstly used in labour economics to assess the returns to schooling (see for example [START_REF] Cornwell | Efficient Estimation with Panel Data: an Empirical Comparison of Instrumental Variable Estimators[END_REF][START_REF] Baltagi | On Efficient Estimation with Panel Data: An Empirical Comparison of Instrumental Variables Estimators[END_REF]Guillotin and Sevestre, 1994), because the unobserved individual ability (specific effects) may be correlated with education. More recently, this method enjoys a great popularity in international economics empirical literature using gravity models owing to many determinants of bilateral trade that are time invariant such as the distance or the common language between two countries (see for example [START_REF] Lochard | Mesurer l'influence des unions monétaires sur le commerce[END_REF][START_REF] Carrère | Revisiting the effects of Regional Trading Agreements on trade flows with Proper Specification of the Gravity Model[END_REF].

As part of our study, the interest of using the methodology developed by HT appears clearly.

It enables to apply a Hausman procedure for testing the joint exogeneity hypothesis of the whole explanatory variables (time-variant and time-invariant) in order to determine the appropriate model between random effects and HT estimators from the perspective of policy implications 10 . Thus, under the null hypothesis of no correlation between unobserved heterogeneity and observable explanatory variables, the random effects estimator and the HT estimator are both consistent, but the random effects estimator is efficient. Under the alternative hypothesis, only the HT estimator is consistent and unbiased.

The Data

The dependent variable is the central government primary budget surplus in percent of GDP (CGPBS) and is taken from [START_REF] Brun | Aide et mobilisation fiscale dans les pays en développement[END_REF]. This measure of budget surplus, which excludes net interest payments by the treasury, is probably the most appropriate measure of fiscal discipline because it assesses the orientation of fiscal policy over the fiscal year.

Furthermore, from an econometric point of view, this measure allows us to avoid a potential simultaneity bias between the dependent variable and the principal explanatory variable.

Indeed, the greater the government influences the monetary authority to monetize deficits, the smaller is the degree of CBI. Thus, if we use the conventional budget balance (which includes public debt interest payments) as an indicator of fiscal stance, a potential endogeneity bias may exist.

The principal explanatory variable is the degree of CBI measured by the two de jure and de facto indicators previously defined. CWN index is given by [START_REF] Crowe | Central Bank Independence and Transparency: Evolution and Effectiveness[END_REF], who compute an updated CWN index for a large set of countries using the International Monetary 10 The Hausman test comparing random effects and HT estimators is as follows: H 0 : difference in coefficients not systematic. . H 0 is rejected and the random effects estimator is inconsistent if Q H > χ 2 r (r denotes the degrees of freedom).

Fund's Central Bank Law Database 11 . Concerning TOR, the authors constructed the data based on central bank websites and central bank survey. The degree of CBI is expected to have a positive effect on budget surplus when it is measured by CWN index. Conversely, we expect TOR to have a negative effect on budget surplus.

We include three regional dummies, RD i: AFRICA for Sub-Saharan Africa, EASIAP for East Asia and Pacific, and LATINCA for Latin America and the Caribbean. The inclusion of regional dummies allows the control of structural characteristics related to geographical location but not to sociopolitical and institutional factors [START_REF] Woo | Economic, political, and institutional determinants of public deficits[END_REF].

In addition to regional dummies, we include other control variables mentioned by many empirical studies on the determinants of public deficits. The determinants of the primary budget balance are on one hand, the capability of a country to mobilize public resources and, on the other hand, the country's allocative efficiency of these resources.

The log of real GDP per capita (LRGDP) is introduced in the regression to capture the differences in the level of economic development between countries. Indeed, although the sample of countries includes only developing market economies, some studies show a relative heterogeneity concerning the level of development of fiscal administrations in developing countries and, therefore, these countries have unequal capabilities to mobilize fiscal resources.

More developed countries, i.e. countries with a relatively high level of fiscal transition, probably have a greater ability to design efficient fiscal systems. So, a higher income per capita reflecting a higher level of development is held to indicate a greater capacity to levy and collect taxes [START_REF] Chelliah | Trends in Taxation in Developing Countries[END_REF]. This is true concerning the management and the efficiency of public expenditures. Moreover, according to [START_REF] Roubini | Economic and political determinants of budget deficits in developing countries[END_REF], the GDP per capita may capture some sociopolitical effects if social conflicts are more important in poor countries.

The sign of GDP per capita is expected to be positive.

The real GDP annual growth rate (GRGDP) is included in the regression as a proxy for economic activity because government budget balance is sensitive to economic fluctuations.

Indeed, when the level of economic activity is low or moderate, the amount of tax revenues collected by the government decreases while social expenditures increase, that leads to a deterioration of budget balance. Conversely, a higher economic growth generates an improvement in the budget balance (automatic stabilizers). Thus, the sign of the coefficient of 11 We would like to thank Christopher Crowe for providing us with the data.

GRGDP is expected to be positive. However, some authors (see for example [START_REF] Talvi | Tax Base Variability and Procyclical Fiscal Policy[END_REF] have suggested that fiscal policy can be procyclical in developing countries with weak governments, because political pressures to increase public spending go hand in hand with the growing tax revenue due to higher economic growth. The strong increase in fiscal demands during economic boom is called "voracity effect" [START_REF] Lane | Voracity Effect[END_REF]. Thus, according to [START_REF] Woo | Economic, political, and institutional determinants of public deficits[END_REF], the sign of the coefficient of GRGDP is an empirical question.

Concerning the urban population ratio (URB), this variable is introduced in the model because [START_REF] Edwards | Explaining Fiscal Policies and Inflation in Developing Countries[END_REF] show that it is relatively easier and less costly for tax authorities to collect taxes in urban areas with higher concentration of the formal sector than in rural areas, where the degree of tax evasion and avoidance is particularly high [START_REF] Ansari | Determinants of Tax Ratio: A Cross-Country Analysis[END_REF]. We then expect URB to have a positive sign.

Furthermore, according to [START_REF] Tanzi | Structural Factors and Tax Revenue in Developing Countries: A Decade of Evidence[END_REF], the country's economic structure is an important factor that could influence the level of taxation. For this reason, the share of agriculture in GDP (AGRI) is included. Nevertheless, the expected sign of AGRI is uncertain because the theory distinguishes two opposite effects of the share of agriculture in GDP on the tax share.

Thus, on the supply side, the share of agriculture in GDP is expected to have a negative effect on tax revenues because political constraints could encourage the government to cut taxation in this sector, often heavily taxed in many implicit ways through import quotas, tariffs, controlled prices for output, or overvalued exchange rates (Bird, 1979;[START_REF] Mitrea | The theory and practice of tax reform in developing countries[END_REF][START_REF] Tanzi | Structural Factors and Tax Revenue in Developing Countries: A Decade of Evidence[END_REF]. Moreover, agricultural sector in developing countries is mainly characterized by subsistence farming and the predominance of small farmers and so, it appears difficult for a government to tax the main foods that are used for subsistence [START_REF] Stotsky | Tax Effort in Sub-Saharan Africa[END_REF]. Conversely, on the demand side, the share of agriculture in GDP is expected to have a positive effect on budget surplus because many public sector activities being city-oriented, the demand for public goods and services and so the public expenditures are theoretically reduced [START_REF] Teera | Determinants of Taxe Revenue Share in Uganda[END_REF]. [START_REF] Woo | Economic, political, and institutional determinants of public deficits[END_REF] includes the ratio of liquid liabilities (M3) of the financial system to GDP (ILLY) as a proxy for the financial market development level, the so-called "financial depth".

According to this author, "countries with highly developed financial markets can more easily finance the fiscal deficit by issuing bonds without having to resort to inflationary finance" (Woo, 2003, p. 393). Thus, the sign of the coefficient of ILLY is expected to be negative.

The trade openness (OPEN) is here measured by the ratio of the sum of exports and imports of goods and services to GDP. This variable assesses the intensity of the national economy's integration into world trade and, to a certain degree, the dependence of an economy on international conjuncture and its sensitivity to changes in international prices. Above all, the trade openness enables the assessment of the relative strength of the external constraint to which the economy is submitted and partly determines the political economy "breathing space", especially concerning fiscal policy [START_REF] Blancheton | Ouverture commerciale, croissance et développement: malentendus et ambiguïtés des débats[END_REF]. Consequently, a country with a relatively high degree of trade openness theoretically may be more vulnerable to external shocks. This increase of vulnerability is not without consequence on government budget balance. However, [START_REF] Combes | How does the trade openness influence budget deficits in developing countries[END_REF] emphasize the contradictory results concerning the effect of trade openness on budget balances in the studies that included this proxy of external vulnerability as a control variable for budget deficits. Moreover, although this measure of trade openness is widely used in empirical literature, it is has been criticized by some economists 12 . Thus, the expected sign of the coefficient of OPEN is uncertain.

Finally, we introduce in the model a currency union dummy (CU) which takes the value of one if the country is a member of a currency union, or zero otherwise. In our sample, accession to currency union concerns fourteen African countries, each affiliated with one of the two monetary unions of the CFA Franc Zone: the West African Economic and Monetary Union (WAEMU) and the Central African Economic and Monetary Community (CAEMC) 13 .

The sign of the coefficient of CU is expected to be positive. Indeed theoretically, these countries must respect a set convergence criteria pertaining notably to public finances, the key criterion being the ratio of the basic fiscal balance 14 to nominal GDP which must be 0 or more. So, we could expect that these budgetary rules, which constrain politician's tax and spending behavior, have a positive impact on primary budget surplus.

12 The principal criticisms made for this measure are : (i) its construction fault (ratio of sales to a sum of value added) ; (ii) its double dependence on political (intensity of commercial protections) and structural (population, dimension). See [START_REF] Siroën | L'ouverture commerciale est-elle measurable?[END_REF] and [START_REF] Blancheton | Ouverture commerciale, croissance et développement: malentendus et ambiguïtés des débats[END_REF] for a comprehensive survey. 13 The eight members of WAEMU are : Benin, Burkina Faso, Côte-d'Ivoire, Guinée-Bissau (who joined in May 1997), Mali, Niger, Senegal and Togo. The six members of CAEMC are: Cameroon, Central African Rep., Chad, Congo Rep., Equatorial Guinea and Gabon. 14 The basic budget balance is defined as total revenue, excluding grants, minus total expenditures, excluding foreign-finance investment.

Results

This section discusses the empirical results for each specification, i.e. for each measure of CBI (de jure and de facto). For each specification, we estimate the panel regression of equation ( 1) using random effects and HT models. In either case, the Hausman test suggests that the non-instrumented regression is more appropriate. Nevertheless, to show the robustness of our results, we present the HT model and random effects panel regression results using the same specification. We then compare the results of the two models. Table 1 shows the results of the influence of legal CBI on primary budget surplus. As stressed by the economic literature on CBI, the estimated coefficient of CWN is insignificant at the conventional level. Thus, this result confirms that a legal approach is not fit for developing countries, characterized by weak institutions which deviate from the law. Concerning the control variables, the estimated coefficients of LRGDP and ILLY are statistically significant and have the expected sign. URB has the expected sign with random effects and the wrong sign with HT model but is not significant. The estimated coefficient of AGRI has a positive sign but is insignificant. OPEN has a positive sign and is significant at the 5 percent level with HT methodology. The sign of the coefficient CU is insignificant in both the models. This last result could be nevertheless explained by the fact that few WAEMU and CAEMC countries have satisfied convergence criteria 15 . Concerning the coefficients on the regional dummies, they are insignificant for Sub-Saharan African and Latin American and Caribbean countries, but are globally significant for East Asian and Pacific countries at the conventional level, reflecting the fact that most of the countries of this region have run higher primary budget deficits than other developing countries. 15 See annual reports drafted by the WAEMU and the CAEMC Commissions for more details. Table 2 reports the results of the influence of actual CBI on budget surplus. The coefficient of TOR appears with the expected sign and is significant at the 1 or 5 percent level. This result means that the turnover rate of central bank governors is negatively associated with primary budget surplus. It suggests that the greater the independence of a country's central bank, the lower is its budget deficit and so, confirms the theoretical predictions which suppose that CBI is a key determinant of budget deficits. We can see that results are robust to various econometric specifications in terms of statistically significance and size of coefficients. Moreover, while the Hausman test suggests the random effects model to be the preferred specification, we see that there are very few differences between random effects and HT models, which lead to very similar coefficients and statistically significance levels. So, our results are not sensitive to the estimation technique and show the robustness of the relation between CBI and budget deficits. Concerning the control variables, results are similar to table 1 and confirm that LRGDP and ILLY are robust determinants with CBI of budgets deficits in developing countries. Finally, coefficients on the regional dummies are uniformly negative and largely insignificant. Only EASIA is significant in the complete random effects model (column 7) at the 10 percent level.

Conclusions and Policy Implications

Theoretical literature argued that CBI should affect the design of fiscal policy, in the sense that a higher independence is associated with lower budget deficits. Nevertheless, the few empirical studies which have sought to econometrically assess this relationship were mainly focused on developed countries, and have found insignificant results. So, using two indicators measuring de jure and de facto CBI, this paper aims to re-examine the effect of CBI on budget deficits in a large sample of developing countries over the 1995-2004 period employing a panel data analysis.

Our empirical results suggest that a significant negative relation exists between CBI and primary budget deficits in developing countries. These results are in accordance with the theoretical literature and mean that, ceteris paribus, a country with a weak independent central bank tends to have higher primary budget deficits. Moreover, we find that the difference between de jure and de facto independence is relevant in developing countries, because actual CBI evaluated by TOR is statistically significant whereas legal CBI measured by CWN index appears insignificant.

The policy implications of these results are clear: CBI must be promoted and consolidated in developing countries in order to exert a disciplining influence on political decision makers who improve fiscal policies. Thus, more disciplined fiscal policies should enable to avoid debt crisis, such as those that have been observed in developing countries prior the adoption of the Multilateral Debt Relief Initiative (MDRI) by international financial institutions in June 2005.

In addition to the increase of CBI, developing countries should also implement structural reforms to define sound budgetary institutions and efficient fiscal administrations. Source: [START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] and [START_REF] Arnone | Central Bank Autonomy: Lessons from Global Trends[END_REF]

  (i) the components contained in the indicators are different because the measures focus on different aspects of CBI; (ii) the interpretation of central bank status by researchers regarding each individual criterion differs; (iii) the indicators are differently weighted combinations of the same components. These limits underline that coding and measuring legal independence is an inherently arbitrary and subjective process.

  organic independence (4) [code: CEO]; monetary policy formulation (3) [code: PF]; monetary policy final objectives (1) [code: OBJ]; limitations of lending to government (8) [code: LL].

  effects, and according to the variables are time-variant or time-invariant. Thus, four sets of right-hand-side variables are distinguished: X1, X2, Z1 and Z2 where X1 is n*k1, X2 is n*k2, Z1 is n*g1, Z2 is n*g2 and, n = N*T. X1 and Z1 are doubly exogenous i.e. they are not correlated with unit specific effects and idiosyncratic error, while X2 and Z2 are endogenous because they are correlated with specific effects but uncorrelated with the error term. The set of variables X (X1, X2) contains variables with intra-individual variability, while the group of variables Z (Z1, Z2) comprises variables with no intra-individual variability. So, from this classification, the presence of X2 and Z2 is the cause of bias in the random-effects estimator and these variables must then be instrumented. As emphasized previously, the originality of HT's methodology is to use information already contained in the model to instrument the variables X2 and Z2. The matrix of instruments suggested by HT is as follows: [QX1, QX2, PX1, Z1] where Q is a projection matrix which transforms a vector of observations into a vector of deviations from group means and, P transforms a vector of observations into a vector of group means. The order condition for identification is that the number of X1

4/

  Limitations on lending to the government a) Limitations on advances -Advance lending to the government is prohibited -Advances are possible with strict limits (e.g. up to 15% of government revenue) -Advances are possible but subject to more accommodating limitations (e.g. over 15% of government revenue) -No legal limitations on advances; amount is periodically negotiated between the central bank and the government b) Limitations on guaranteed loans to the government Same distinctions as for Lla c) Who has authority to control terms and conditions of loans to the government? -Central bank -Terms and conditions specified by the central bank law -Terms and conditions agreed between the central bank and the executive branch -Terms and conditions decided by the executive branch alone d) Who has access to loans granted by the central bank? -

Table 1 : The influence of de jure independence (CWN index) on budget surplus

 1

	The dependent	RE	RE	RE	RE	RE	RE	RE	HT
	variable is primary	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
	budget surplus
	INTERCEPT	-15.53***	-14.99***	-14.22**	-17.14**	-12.99	-12.17	-12.21	-8.177
		(4.999)	(5.049)	(5.665)	(8.481)	(8.802)	(8.853)	(8.910)	(15.36)
	EASIAP	-3.744	-3.664	-3.595	-3.432	-2.656	-3.965	-3.991	-5.289
		(2.659)	(2.680)	(2.710)	(2.738)	(2.747)	(2.885)	(2.911)	(5.511)
	LATINCA	-3.919*	-3.668*	-3.711*	-3.404	-4.600**	-4.759**	-4.843**	-3.415
		(2.145)	(2.170)	(2.190)	(2.263)	(2.331)	(2.349)	(2.379)	(4.551)
	AFRICA	0.626	0.556	0.564	0.745	-1.019	-1.839	-1.578	-3.829
		(1.763)	(1.777)	(1.792)	(1.818)	(2.035)	(2.113)	(2.264)	(4.278)
	CWN	1.458	1.116	0.682	-0.317	-3.595	-3.808	-3.784	-9.436
		(4.683)	(4.726)	(4.968)	(5.218)	(5.469)	(5.509)	(5.559)	(11.32)
	LRGDP	2.450***	2.365***	2.191***	2.574**	2.565**	2.348**	2.345**	3.347*
		(0.547)	(0.554)	(0.792)	(1.078)	(1.083)	(1.094)	(1.101)	(1.743)
	GRGDP		0.0494	0.0511	0.0501	0.0388	0.0277	0.0280	0.0174
			(0.0377)	(0.0381)	(0.0385)	(0.0390)	(0.0404)	(0.0404)	(0.0405)
	URB			0.0138	0.0158	0.0327	0.0353	0.0372	-0.0985
				(0.0448)	(0.0454)	(0.0460)	(0.0463)	(0.0472)	(0.0790)
	AGRI				0.0293	0.0257	0.0255	0.0272	0.00559
					(0.0587)	(0.0600)	(0.0603)	(0.0607)	(0.0774)
	ILLY					-0.0430*	-0.0501**	-0.0513**	-0.0736**
						(0.0227)	(0.0232)	(0.0235)	(0.0324)
	OPEN						0.0226	0.0232	0.0345**
							(0.0142)	(0.0144)	(0.0175)
	CU							-0.637	0.0303
								(1.768)	(3.430)
	Observations	508	508	508	499	494	493	493	493
	Nb. of countries	56	56	56	55	55	55	55	55
	R 2	0.32	0.31	0.32	0.33	0.35	0.35	0.35	-
	Hausman Test								6.64
	Note: Standard errors are reported in brackets. Columns (1) to (7) present the random effects (RE) estimates.
	Column (8) reports the estimate with Hausman Taylor (HT) estimator. Levels of significance are indicated by
	asterisks: *** 1%, ** 5%, * 10%. Variables X1: GRGDP, URB, AGRI, ILLY, OPEN; Z1: EASIA, LATINCA,
	AFRICA, CWN, CU; X2: LRGDP.

Table 2 : The influence of de facto independence (TOR) on budget surplus

 2

	The dependent	RE	RE	RE	RE	RE	RE	RE	HT
	variable is primary	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
	budget surplus
	INTERCEPT	-6.981**	-6.895**	-6.613*	-6.944	-7.071	-6.208	-6.007	11.41
		(3.480)	(3.502)	(3.602)	(5.748)	(5.614)	(5.637)	(5.677)	(8.661)
	EASIAP	-2.232	-2.201	-2.134	-2.113	-2.072	-2.429	-2.342	-1.502
		(2.204)	(2.218)	(2.237)	(2.239)	(2.169)	(2.259)	(2.282)	(2.283)
	LATINCA	-1.747	-1.659	-1.738	-1.534	-3.159*	-3.026*	-2.986*	-1.524
		(1.540)	(1.551)	(1.573)	(1.607)	(1.719)	(1.730)	(1.740)	(1.823)
	AFRICA	-1.404	-1.456	-1.354	-1.295	-2.595*	-2.713*	-2.583	-3.055*
		(1.362)	(1.371)	(1.406)	(1.407)	(1.481)	(1.557)	(1.604)	(1.606)
	TOR	-11.80***	-11.76***	-11.40**	-12.01***	-11.43**	-11.16**	-12.21**	-14.22***
		(4.404)	(4.433)	(4.566)	(4.636)	(4.493)	(4.519)	(5.354)	(5.406)
	LRGDP	1.714***	1.677***	1.530***	1.599**	1.951**	1.758**	1.758**	-0.440
		(0.437)	(0.441)	(0.592)	(0.764)	(0.761)	(0.770)	(0.773)	(1.298)
	GRGDP		0.0389	0.0403	0.0388	0.0294	0.0329	0.0333	0.0373
			(0.0338)	(0.0340)	(0.0343)	(0.0345)	(0.0350)	(0.0350)	(0.0358)
	URB			0.0128	0.0128	0.0177	0.0182	0.0197	0.0234
				(0.0341)	(0.0343)	(0.0334)	(0.0337)	(0.0341)	(0.0397)
	AGRI				-0.000316	0.00184	-0.00316	-0.00105	-0.116*
					(0.0484)	(0.0476)	(0.0483)	(0.0488)	(0.0629)
	ILLY					-0.0375**	-0.0366**	-0.0377**	-0.0353*
						(0.0168)	(0.0173)	(0.0176)	(0.0183)
	OPEN						0.00660	0.00683	0.00712
							(0.0110)	(0.0110)	(0.0112)
	CU							-0.602	-0.623
								(1.641)	(1.615)
	Observations	707	707	707	696	696	694	694	694
	Nb. of countries	77	77	77	76	76	76	76	76
	R 2	0.29	0.29	0.29	0.3	0.34	0.33	0.33	-
	Hausman Test								8.71
	Note: Standard errors are reported in brackets. Columns (1) to (7) present the random effects (RE) estimates.
	Column (8) reports the estimate with Hausman Taylor (HT) estimator. Levels of significance are indicated by
	asterisks: *** 1%, ** 5%, * 10%. Variables X1: GRGDP, URB, AGRI, ILLY, OPEN; Z1: EASIA, LATINCA,
	AFRICA, TOR, CU; X2: LRGDP.

  Limitations on interest rates applicable to loan by central bank -Loan is possible only at market rates -Minimum level applies to interest rates paid by the government -Ceiling applies to interest rates paid by the government -No explicit legal provisions on interest applied to loans by the central bank -Law does not provide for the government to pay interest on loans from the central bank h) Prohibitions on lending on the primary market -Central bank prohibited from underwriting public debt securities on the primary market -Central bank may underwrite public debt securities on the primary market

	Only the central government All levels of government All levels of government and public enterprises Public and private sector e) Types of limitations on loans, where limits exist ----Limit on loan amount is prescribed in absolute terms -Limit on loan amount is prescribed in terms of capital or other liabilities of the central bank -Limit on loan amount is prescribed in terms of percentage of government's revenues -Limit on loan amount is prescribed in terms of percentage of government's expenditures f) Maturity of possible loans -< 6 months -< 1 year -> 1 year -No legal limit on maturity of loan g) LL Lla Lls Ldec Lwidth Ltype Lmat Lint	0.50 0.15 0.10 0.10 0.05 0.025 0.025 0.025	1.00 0.67 0.33 0.00 1.00 0.67 0.33 0.00 1.00 0.67 0.33 0.00 1.00 0.67 0.33 0.00 1.00 0.67 0.33 0.00
			1.00
			0.75
			0.50
			0.25
			0.00
	Llprm	0.025
			1.00
			0.00

See Eijffinger and De Haan (1996) for a detailed survey.

See Appendix A for most details concerning empirical studies on the relationship between CBI and budget deficits.

The distinction between goal independence and target independence is due to[START_REF] Lybek | Central Bank Autonomy, and Inflation and Output Performance in the Baltic States, Russia, and Other Countries of the Former Soviet Union, 1995-97[END_REF], while[START_REF] Debelle | How Independent Should a Central Bank Be?", Goals, Guidelines and Constraints Facing Monetary Policymakers[END_REF] only distinguish goal/target independence and instrument independence.

According to[START_REF] Bassoni | Autonomie des banques centrales et performances macroéconomiques. Un réexamen[END_REF], financial independence and budgetary independence are equivalent concepts. However, in this paper, we distinguish these two concepts.

See Appendix D and Cukierman et al. (1992) for a detail description of the CWN index, its subcomponents and, its coding and weighting system.

These three measures are TOR, Political vulnerability index and an index based on responses to a questionnaire provided by specialists. See[START_REF] Cukierman | Measuring the Independence of Central Banks and its Effect on Policy Outcomes[END_REF] and[START_REF] Cukierman | Political Influence on the Central Bank: International Evidence[END_REF] for a thorough description of these indicators.

Note, however, that a recent methodology, the unit fixed effects vector decompostion, developped by[START_REF] Plümper | Efficient Estimation of Time-Invariant and Rarely Changing Variables in Finite Sample Panel Analyses with Unit Fixed Effects[END_REF] allows the use of a fixe effects model in presence of time-invariant variables.

Appendix A. Empirical studies on the relationship between CBI and budget deficits

Study

Countries Period CBI index Relation between CBI and budget deficits [START_REF] Masciandaro | Monetary Regimes and Fiscal Deficit: A Comparative Analysis[END_REF] 5


 Guinard
email: luc.guinard@edf.fr

CHARACTERIZATION OF CONTAMINATION: FRENCH ANALYSIS OF INTERNATIONAL EMECC CAMPAIGNS

The reduction in collective dose is an important objective for all nuclear plant operators. One of the ways for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs.

EDF' strategy is based on several levels of measurement: local dose rates give raw information; dose rate index and CZT spectrometry allow an evaluation of the radiological situation of each plant, its evolution and comparison with other plants. For very accurate characterization, EDF performs gamma spectrometry measurements with CEA and its EMECC system, with more than 300 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators.

Recent collaboration between EDF and other operators with excellent collective dosimetry resulted in measurements during several Refuelling Outages. The present paper presents results obtained with EDF Energy at Sizewell B Outage 8, ELECTRABEL at Doel 3 Outage 25 and Doel 4 Outage 22 and CNAT at Trillo Outage 21. The paper presents the results in terms of deposited activities and dose rates in RCS and CVCS, and compares them with French PWRs, and especially with Saint-Laurent B1.

The specificities of all these plants are identified, to explain the differences in results, either for dose rates, deposited activities or collective dosimetry. All these comparisons will enable EDF and collaborative operators to improve the performance of their own plants.

INTRODUCTION

The reduction in collective dose is an important objective for all nuclear plant operators. One of the ways for studying the impact of design and operation parameters is the measurement campaigns of contamination in PWRs.

EDF' strategy is based on several levels of measurement: local dose rates give raw information; dose rate indexes (RCS and RB indexes) and CZT spectrometry allow an evaluation of the radiological situation of each plant, its evolution and comparison with other plants, useful in particular to determine on which unit a cleaning process is needed and which kind of specific process have to be applied. For very accurate characterization, EDF performs gamma spectrometry measurements with CEA and its EMECC system [START_REF] Eimecke | Ensemble de Mesure et d'Etude de la Contamination des Circuits[END_REF], with more than 300 campaigns in EDF plants and also about 70 campaigns in collaboration with other operators.

EMECC CAMPAIGN AT SIZEWELL B

Plant measurements

Sizewell B is a Westinghouse 4-loop PWR with alloy 690TT tubed steam generators (SGs). This unique British PWR is characterized by very low corrosion product releases and radiation fields [START_REF] Bates | Development of Corrosion Product Behaviour and Radiation Fields at the Sizewell B PWR from 1995 to 2008[END_REF]. In order to compare the contamination level of Sizewell B to that of French PWRs, an EMECC campaign was conducted during the refuelling shutdown at the end of cycle 8. The reactor coolant chemistry is boron-lithium coordinated chemistry with a target pH 300°C of 7.2. Unlike most of French units , lithium can be over 2.2 mg/kg, till 3.5 mg/kg. The H 2 target concentration ranges between 30 and 45 cm 3 /kg, slightly higher than French range (25 -35 cm 3 /kg). Cycle 8 lasted 475 EFPD [START_REF] Guinard | Characterization of contamination : EMECC campaign at Sizewell B and comparison with French PWRs[END_REF].

All the results will be compared with measurements performed at Saint-Laurent B1 during the refuelling shutdown at the end of cycle 20. Indeed, Saint Laurent B1 is an AREVA 3-loops PWR with alloy 690TT tubes SG and equivalent duration of operation since SG replacement (performed after cycle 11).

Deposited activities

The deposited activities are presented in figure 1 Co (about 7% each). The comparison with St-Laurent B1 for RCS shows similar dose rates whereas 60 Co surface activities are higher in Sizewell B08. Sizewell has the benefit of thicker component walls (e.g. SG shell thickness: 9.7 cm in Sizewell B compared with 8.5 cm in St Laurent B1; hot leg thickness: 8.3 cm in Sizewell B compared with 6.9 cm in St Laurent B1). For CVCS letdown pipe, the dose rates are higher at Sizewell B08, due to higher surface activities and thinner walls. Conversely for letdown heat exchanger, the dose rates are lower in Sizewell B08, due to high 110m Ag contamination in St Laurent B120.

PaperFigure 2 .

 2 Figure 1. 58 Co RCS surface activities -Comparison Sizewell B / Saint-Laurent B1.

Figure 3 .

 3 Figure 3. Primary piping and SG tube bundle: CEA index

2. 4 . 4 3. 1

 441 Figure 4. 58 Co and

  The comparison on low level contamination plants gives elements to improve the behavior of the plants. Consequently, recent collaboration between EDF and other operators with excellent collective dosimetry resulted in measurements during several Refuelling Outages. This paper presents results obtained with EDF Energy at Sizewell B Outage 8, ELECTRABEL at Doel 3 Outage 25 and Doel 4 Outage 22 and CNAT at Trillo Outage 21.

2.3. Dose rates Dose

  rate measurements were performed around the RCS for estimating CEA index (see figure3and table1).

	for concerning CVCS letdown pipe and letdown heat exchanger are available in [3]. 58 Co in RCS and figure 2 for 58 Co and 60 Co in RCS. Other data 60 Co contribute 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 58 Co or 60 Co. The only main other nuclide for dose rate contribution is 110m Ag for CVCS letdown
	heat exchanger (about 7%). Comparison with St-Laurent B1 for RCS shows similar contamination for	58 Co and higher 60 Co surface activities in
	Sizewell B08.
	The Co contribution is higher: Co. 58 58 Co is the major contributor to the dose rates around the Co is higher than 90%: 70% to 85% for 60 60 Co, 10% to 20% for For CVCS, dose rate measurements are presented in table 2. For letdown pipe, the contribution of 58 Co and 30% compared with 60% for 60 Co due to the thinner pipe. 60 letdown heat exchanger (75%), with 110m Ag and 58

Table 1 .

 1 Dose rates around primary system (CEA index -mSv/h) -Comparison Sizewell B / Saint-

	Laurent B1.
		SIZB08	SLB120
	Primary piping	0.19	0.28
	SG tube bundle	0.10	0.08

Table 2 .

 2 Dose rates at CVCS (mSv/h) -ComparisonSizewell B / Saint Laurent B1.

		SIZB08	SLB120
	Letdown pipe	2.0	0.8
	Letdown heat	0.15	2.3
	exchanger

/kg. During shutdown, oxygenation is performed at full loop by means of hydrogen peroxide injections[START_REF] Schnongs | Primary chemistry as an action lever to reduce the source term. Review of the experience at Doel 3 and 4[END_REF].

Deposited activities

The deposited activities are presented in figure 5

Dose rates

Dose rate measurements were performed around the RCS and the letdown heat exchanger (CVCS) to estimate CEA index (see table 3). These figures are slightly lower than those for Saint Laurent, but higher than those for Sizewell. In Trillo-1 during cycle 21 (281 EFPD), the reactor coolant was based on a boron-lithium coordinated chemistry with a pH 300°C target of 7.5. Almost immediately at the beginning of cycle 21, pH 300°C rose above 6.9 whereas the maximum Li content remained quasi-stable at about 2.2 ppm for 80% of the cycle duration. This procedure is slightly different from the French one for which the pH 300°C target is 7.2 (optimum chosen by EDF between contamination risk and potential PWSCC long term risk with high lithium concentration).

During cycle 21, H 2 concentration in the primary coolant ranged between 22 and 28 cm 3 /kg , with an average of 24 cm 3 /kg [START_REF] Ranchoux | EMECC campaign at Trillo : results and comparison with french feedback[END_REF]. The average dose rate measured around the primary piping is higher in Trillo 1 Cycle 21 than at St Laurent B1 Cycle 20, due to higher 60 Co surface activities (factor 2) and to a lower wall thickness (about 6 cm at Trillo compared to 6.9 cm at St Laurent B1). The lower dose rate index of the Trillo SG tube bundle is due to a higher SG shell thickness (10 cm in Trillo compared to 8.5 cm in St Laurent B1).

Deposited activities

The dose rate close to the non regenerative heat exchanger is 10 times lower in Trillo 1 than in St Laurent B1, essentially due to the contamination caused by 110m Ag which is the major contributor (about 65% to 80%) whereas 60 Co contribute only 15% to 20%.

Volume activities

The average of volume activities during Trillo 1 cycle 21 is about 2 MBq/t 58 Co and 1 MBq/t 60 Co. One can observe that the volume activities in CNT121 are very slightly lower than those measured in St Laurent B1.

COLLECTIVE DOSIMETRY

The comparison (see figure 9) between Sizewell B, Doel 3 & 4, Trillo, St-Laurent B1 and N4 units (1450 MWe French units called F43 sister units) ranges roughly from the lowest to the highest collective dosimetry: Doel 4, then Sizewell B, Trillo and N4 units, then Doel 3 and finally St-Laurent B1. All the data are of the same magnitude and St Laurent B1 demonstrated a significant improvement over the last decade, due to efficient ALARA plans. The comparison of dose rate index or deposited activities is slightly different, from the lowest to the highest: Doel 4, then Sizewell B, St-Laurent B1 and N4, then Trillo and finally Doel 3. For most data, dosimetry follows dose rates and data underline the impact of source term management. Where this is not the case, other factors must be taken into account.

DISCUSSION

The differences between the NPPs are now to be discussed, to find explanations and ways of improvement.

Because of importance of source term, design and operation will first be reviewed. Other causes have also to be found.

Design

As the main contributors to dose rate are 60 Co and 58

Co, the chemical elements to be limited are Co and Ni. The main potential reasons for higher 60 Co contamination are the SG tubing Co content, stellites and Inconel grids. The SG tubing Co content is low for all the studied NPP: below 150 ppm either in Sizewell B, St-Laurent B1 and Trillo, 120 ppm in Doel 3 and 210 ppm in Doel 4. This low content is beneficial, but doesn't explain differences: the higher content is fitting the "best" unit. Stellite reduction can also partly explain the best behaviour of Doel 4, compared with Doel 3. Sizewell B (CVCS valves) and Trillo also experienced the beneficial effect of stellite reduction. However; they are more 60 Cocontaminated than St-Laurent B1. Last, the impact of Inconel 718 grids can explain differences of 60 Co between Sizewell B and St Laurent B1: for the first cycles in Sizewell B, all assemblies were equipped with Inconel 718 grids. A major part has been replaced, but there were still 13 assemblies equipped with Inconel 718 grids during cycle 8 (and 0 for St Laurent B1). 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 60 Co contamination for many cycles because of 60 Co radioactive half-life (5.3 y). A similar explanation can be proposed for the comparison between Doel 3 and Doel 4: more Inconel grids and higher level of 60 Co contamination for Doel 3. Furthermore, Inconel 718 fuel grids could be the main cause of Trillo 60 Co contamination. In fact, since the beginning, fuel assemblies at Trillo have always contained Inconel 718 grids. During the four first cycles, all fuel spacer grids were made of Inconel 718. Afterwards and until cycle 17, only bottom and top grids were made of Inconel 718, the others grids being made of Zircaloy-4. More recently, the refuelling assemblies have been made with a bottom fuel grid made of Inconel 718 and the others made of HPA-4. Since the Co specification of alloy 718 grids was high (1000 ppm), it is possible that the grids (activated by intense neutron flux) have directly released 60 Co into the primary coolant leading to a 60 Co contamination build-up.

The main potential reason for higher 58 Co contamination is the release of nickel from SG tubing. The choice of SG tubing alloy can be discussed: In spite of the very low corrosion release rate of alloy 690 SG tubing, due to improved manufacturing process, iron based alloy 800 allows theoretically lower 58 Co contamination than nickel based alloy 690. It is confirmed here for both units equipped with 800 alloy: Trillo and Doel 3 (excepted for the cold side of Doel3 SG). However, it is obvious that this is not the main parameter for low dosimetry: the lowest dosimetry is achieved by Doel 4 with 690 alloy.

As a conclusion, there are a lot of beneficial parameters, individually necessary but not sufficient to improve contamination behaviour: it is necessary to reduce not only Co content, but also Stellite inventory and use of Inconel grids.

Operation

Operating parameters are very similar between Saint-Laurent B1 and Doel 3 & 4 ; there are some differences in Sizewell B (longer cycle and higher lithium content at beginning of cycle) and Trillo (higher pH), but these parameters are not known to change the contamination significantly in their limited range [START_REF] Guinard | General overview of the evolution of international collective radiation exposure and associated good practices[END_REF]. Last, we can note that volume activities are quite different, with lowest values for Sizewell, highest for Saint-Laurent, and intermediate for Trillo and Doel. However, there is no correlation with volume activities during shutdowns and surface activities, which can be similar. We are not convinced that such differences have any impact on contamination, but this topic should be further investigated.

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). The shortest duration is in Doel (about 30,000 h) and Trillo is intermediate (about 60,000 h). Consequently, Doel 4 performs lowest dosimetry with lowest duration, but Trillo and Sizewell perform lower dosimetry than St Laurent and Doel 3 with higher duration. At first analysis, it could seem contradictory to "logical" and international trends [START_REF] Guinard | General overview of the evolution of international collective radiation exposure and associated good practices[END_REF]: the reduction of time is one of the main contributors for RP improvement. This analysis has consequently to be completed by examining the differences in organization. Concerning Sizewell B, it appears firstly that people work less "alone" during outages, with almost systematically one Health Physician together with each work team. This organization has two direct consequences: it can improve the working conditions and it increases "artificially" the time spent in the controlled area. Another possible difference is less time in dosing outage operations, as for instance less work for SG inspections. Concerning Doel, main differences of interest are the generalised use of particular devices, such as fixed biological protection and permanent anchors. Other potential causes of differences have to be evaluated:

differences in contamination of auxiliary systems, even if first results on CVCS (See 2.3) 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).

CONCLUSION

A fruitful comparison between EDF and some of the best European NPP has been conducted, using the EMECC campaigns. Deposited activities measurements and dose rate index are very consistent. These data are often consistent with collective dosimetry, but not always. For most data, dosimetry follows dose rates and data underline the impact of source term management. Where this is not the case, other factors must be taken into account. Concerning Source Term reduction, good practices are evidenced. For the design, it is mainly removal of stellites, Co low content of SG tubes and in-core materials, and specially Inconel grids. For operation, there are no big differences, even if each operator has his own procedures. Significant differences in volume activities are observed without any direct link with contamination.

Improvement of organization is also of interest. For instance, generalised use of particular devices, such as fixed biological protection and permanent anchors is underlined. Training also remains an essential tool for preparing maintenance.

Some items remain to be further explored: higher improvement of organization, complementary information exchanges on impact of auxiliary systems contamination or differences in volume activities. Measurement campaigns on auxiliary systems have already been performed, but could be completed, and particularly with CZT campaigns [START_REF] Bonnefon | CZT technology application at EDF for better radiation protection and nuclear plant surveillance[END_REF].

Exchanges with other operators will ever be a dynamic complement to internal studies, allowing EDF and its partners to improve the performance of their own plants.