Audrey Vicenzutto

Xavier Saloppé

Arkhipova Olga

Thomas Deviviers

Thierry H Pham

Implementation of Miyake task in psychopathic forensic sample: an exploratory research

Introduction

Much research has been conducted on the associations between the concept of psychopathy and executive functions (Bagshaw, Gray, & Snowden, 2014;Blair & al., 2006 ;Mol, & al., 2009 ;Pham, & al., 2003). Psychopathic patients have difficulties on attentional management, behavioral inhibition and planning (Arnett, Smith, & Newman, 1997;Kosson and Newman, 1986 ;Newman, Patterson, Howland, & Nichols, 1990). However, no study has yet assess the executive function tasks in psychopathy using Miyake Task.

Executive function assessment in psychopathic forensic sample Implementation of Miyake task: an exploratory research

Vicenzutto, A. 1 ; Saloppé, X. 2, 3, 4, 5 ; Deviviers. T.

Method Instruments

The Psychopathy Checklist -Revised (PCL-R;Hare, 2003) is a 20-item scale composed of two factors. The factor 1 evaluates personality traits including emotional aspects and interpersonal tendency. The factor 2 evaluates chronic antisocial tendency. Both factors may each be divided into two facets: factor 1 is divided in the Interpersonal facet (facet 1) and the affect deficit (facet 2) and factor 2 is composed of the impulsivity and parasitic lifestyle (facet 3) and chronic antisocial behavior (facet 4)

The Computerized Miyake Task assess three executive functions, precisely: mental set shifting, information updating and monitoring, and inhibition of prepotent responses (Miyake, Emerson, Witzki, Howerter, & Wager, 2000). Each function is assessed by three subtests .

.

Discussion

Results show significant negative correlations between the PCL-R scores, Factor 1 (and facets 1 and 2) and the performances at the Stroop, particularly, the reaction time. These results suggest that the higher the Factor 1, the lower the reaction time, which did not a Impair the success rate. In term of inhibition, this factor allows the patient to be functional. On the other hand, significant negative correlations for the subtest Number-Letter (Shifting) indicate that the higher the score on Factor 2, especially in the facet 4, the lower are the success rate at this subtest.

Clinical implications

In contract to most studies concerning executive function deficits in psychopathy, this study implemented a more specific measure of executive function among a forensic population testing the equipment in clinical conditions. These first observations highlight several difficulties with the computerized Miyake Task: the length of the administration (several sessions) and the difficulty of several tasks caused a loss of motivation among patients. Moreover, several tasks require alphabet knowledge or reading abilities, which are not accessible to some patients.

Conclusion

The results suggest some Inhibition and Shifting response specificities. These findings encourage further research on the executive functioning in psychopathy through the implementation of specific measures of executive functions. The results need to be considered with caution. Indeed, we conducted an exploratory research, with a small sample size. We did not control psychiatric comorbidities, which may alter cognitive tests performances.

Contact : audrey.vicenzutto@umons.ac.be / thierry.phamhoang@umons.ac.be

Sample

Our sample included 20 males forensic inpatients from the secure psychiatric hospital of the C.R.P. « Les Marronniers » in Belgium. The mean age is 45.92 years (SD = 12.02). The mean length of stay is 6.11 years (SD = 5.33). The mean total IQ score is 67.3 (SD = 10.67).

Procedure

We excluded patients in acute phase. Each participant signed an informed consent sheet.

Data analysis

Because of non normality (Shapiro-Wilk test), we performed Spearman nonparametric correlations between the PCL-R factors and performances at the computerized Miyake task.

.

Descriptives statistics

Correlation with PCL scores


Romain Petre-Bordenave
email: romain.petrebordenave@fialab.eucedric.seguineau@fialab.eu

Cédric Seguineau

Lucie Thebault

Jean-Michel Desmarres
email: jean-michel.desmarres@cnes.fr

Joël Alexis
email: joel.alexis@enit.fr

Quantification of the pile-up effect for improving inverse mechanical analysis by means of nanoindentation

This paper deals with the identification of elasticplastic material properties by means of nanoindentation. A dimensional analysis leads to the identification of a specific parameter based on the estimation of the pile-up effect. This parameter may be used in an inverse analysis. Theoretical aspects and experimental issues are discussed.

Nanoindentation, inverse analysis, pile-up, plastic properties I.

INTRODUCTION

The utility of thin-films coatings for microelectronics is not to demonstrate. The evaluation of the properties of such coatings requires fitted experiments such as nanoindentation. For 3 decades, practical methods have been developed and are now commonly used to determine elastic parameters such as Young's modulus [START_REF] Oliver | Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology[END_REF]. These methods are based on the exploitation of the load-displacement curve obtained by nanoindentation. However, new applications like flexible integrated circuit (IC) require tools for the determination of elastic but also, plastic material parameters such as the hardening exponent or the yield strength. Insofar as nanoindentation loading imposes an elastic-plastic deformation of the sample, this kind of experiment should be suitable for the plastic parameters determination.

The determination of plastic properties of small volumes, like BGA interconnect, are also concerned insofar as nanoindentation is commonly used to probe the mechanical properties of cross-sectioned balls. The process and microstructural features of the raw material have a great impact on the quality of the final interconnection. The approach exposed in this paper may provide new relevant data on the plastic behavior of BGA balls.

In this paper, we will focus on the pile-up volume measurement (V b ) in order to identify elastic-plastic parameters.

I. THEORY

The usual approach is based on the Oliver & Pharr method [START_REF] Oliver | Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology[END_REF]. Young's modulus and hardness are the two material properties that can be identified using standard method. In order to determine plastic parameters like the hardening exponent as well as the yield strength, new parameters must be extracted from the nanoindentation experiments.

Several authors work on the use of several geometries of diamond tip. It is well established now that the use of a single pyramidal tip leads to multiple solutions on the yield's stress and the strain hardening coefficient [START_REF] Dao | Computational modeling of the forward and reverse problems in instrumented sharp indentation[END_REF]. Several authors work on the use of a spherical tip in order to deal with this issue [START_REF] Zhao | A new approach to measure the elastic-plastic properties of bulk materials using spherical indentation[END_REF], and other ones have developed a reverse analysis based on the use of at least two pyramidal tips (often a Berkovich and a cube corner tip) [START_REF] Kermouche | Extraction of stress-strain curves of elastic-viscoplastic solids using conical/pyramidal indentation testing with application to polymers[END_REF][START_REF] Bucaille | Determination of plastic properties of metals by instrumented indentation using different sharp indenters[END_REF]. The use of a spherical tip may introduce awkward effects because of its higher sensitivity to roughness and the difficulty to probe small volumes (like a cross-section BGA). On the other hand, the use of several pyramidal tips is time consuming and the current associated reverse analyses tend to lack of robustness.

Another approach may be based on the measure of second order effects while indenting the material with only one tip. The main difficulty is to determine a measure which is independent from the two previous measures. That is why we have focused on measures independent from the nanoindentation curve, where lot of authors have already considered parameters like the residual depth or the irreversible work [START_REF] Fischer-Cripps | A review of analysis methods for submicron indentation testing[END_REF]. For example, the method developed by Tunvisut is based on the accurate measurement of imprint contact area [START_REF] Tunvisut | Determination of the mechanical properties of metallic thin films and substrates from indentation tests[END_REF]. From our point of view, one of the most important second order effect is the pile-up effect around the tip. Indeed, for elastic-plastic materials, the material tend to flow around the tip and to form an irreversible pile-up around the tip. Its volume should be dependent of several material properties and of the geometry of the tip. In order to keep the useful scale independent behavior of the Berkovich indentation, the ratio of the pile-up volume on the indent volume should be considered.

A dimensional analysis was performed using the Vaschy-Buckingham theorem. To perform this analysis five parameters were considered as relevant: h m , E, Y, n and θ (Fig. 1). h m is the maximal depth of penetration , E is the reduced Young's modulus (eq. 1), Y is the Yield strength of the material, n is the hardening exponent and θ is the apical angle of the nanoindenter tip.

Figure 1. Height measurements of an imprint [START_REF] Oliver | Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology[END_REF] This analysis leads to an implicit relationship expressed as follow: , , . As a consequence, three influencing factors are identified. Resolving the corresponding equations stays the second step, and has been addressed with a specific experimental design. In the first place, mixed-effects were not studied.

In this study, two materials were tested in order to have different hardening exponents n, pure copper and 2024 aluminum alloy. Three indenter tips were used to make θ vary, a Cube corner tip, a Berkovich tip and a 3 faces 50° tip. Finally, the ratio ψ=Y/E was modified by work-hardening on a tensile testing machine. In order to perform the hardening, shoulder flat specimen were chosen. These specimens were also annealed to remove the hardening induced by thermomechanical treatments. In these conditions, we can obtain a controlled hardening rate (in the tensile direction).

II. RESULTS

From an experimental point of view, the measurement of V b is a relatively important source of inaccuracy. The difficulty of this measurement lies in the ability of the operator to determine accurately the border between the pileup and the unaffected surface of the specimen.

Several methods were evaluated in order to estimate the pileup volume. These methods are based on surface alignments and zero detection. Multiplying methods and operators lead us to estimate the current uncertainty of the method to about 50%.

The reduction of that error was a priority and was performed using a motorized table embedded with the nanoindentation setup. This system consists in a piezoelectric sample-holder that permits to move the sample over two axes. The scan is performed by using this system in combination with the nanoindenter tip. The scanning is done thanks to the table whereas the nanoindenter tip records the height of each point like an AFM in contact mode.

The AFM and the nanovision scan have been compared. On the one hand the AFM offers a greater accuracy thanks to a smaller apex angle, a reduced tip defect and a more accurate Z-sensor. On the other hand the embedded scan can be used for a subtraction of the initial surface roughness as previously described. The embedded scanning system requires the application of a small force on the tip in order to hold to contact with the sample surface. This force is much greater than the one used in AFM in contact mode. This can lead to a height measurement error due to the elastic compression of the sample surface. Differences up to 3 nm were observed between AFM height measurement and the embedded ones on aluminum 2024. That error proved to be constant and independent of the method of analysis. In our case, a new step was added prior to the indentation: a first scanning of the sample surface is done, and the imprint topography is obtained without any roughness by doing the subtraction of the two scans (Fig. 2). Even if the precision of the method is reduced by 5, the accuracy of the method cannot be evaluated without measures on a standard volume. Indeed, the scattering of 50% should be considered on the AFM topography insofar no initial scan can be performed.

In addition, as the bias induced by the applied force is constant, its effect on the pile-up volume measurement can be minimized by increasing the indent depth and hence the pile-up volume.

The inverse analysis performed during this study showed that important errors were due to the neglect of mixedeffects. In order to study those effects with a sufficient accuracy 54 experiments are needed. With a view to simplifying the experimentation, the numerical simulation can be used [START_REF] Fourcade | Caractérisation de matériaux en couches minces[END_REF], after the EF modeling were properly fitted to the first experimental results. The goal is here to perform an inverse analysis in order to obtain the same properties by nanoindentation than the properties extracted from a tensile test.

CONCLUSION

Nanoindentation is considered as one of the most convenient mechanical test to evaluate some mechanical properties of materials. In several applications, especially on microelectronics and MEMS technologies, nanoindentation is the only test available to probe the mechanical properties of thin layer, interconnects or other heterogeneous assemblies. Nonetheless, while Young's modulus is an intrinsic parameter, hardness is not and mainly depends on plastic properties and geometrical effects. In this paper, we have studied the pile-up effect in order to provide a third parameter from the indentation experiment which should be used to estimate intrinsic plastic properties from the experiment (yield stress and strain-hardening coefficient). This parameter is seldom used in the literature insofar as its measure is subjected to high uncertainties. The latter are mainly linked to the small height at stake and involve complementary analyses. In this paper, these two experimental difficulties were addressed when determining a pile-up volume.

We considered the use of a motorized sample holder coupled with the use of the nanoindenter tip like an AFM to probe the height of the surface, before and after the indentation. Subtracting the two surfaces was found to be accurate enough to reduce the uncertainty from 50% to 10%. A comparison with AFM measurement trends to prove that the load applied to keep contact between the tip and the surface lead to a constant bias of about 3 nm on the height evaluation, which may lead to a systematic bias of about 20% on the pile-up volume. More studies should be performed to deal with this systematic bias. This approach is based on hypotheses on the nature of parameters ruling the pile-up behavior. It appears that the friction coefficient may be a parameter of interest in order to improve the accuracy of inverse analysis. Indeed, few publications mention the study of this parameter on the mechanical behavior of the material under the diamond tip. Adam and Swain have recently exposed that this parameter seems to have a limited impact on the depth volume of bones material (10 to 20%) while the impact on the pile-up is much greater, with a reducing of 50 to 75% of the predicted height of the pile-up [START_REF] Adam | The effect of friction on indenter force and pile-up in numerical simualtions of bone nanoindentation[END_REF]. The ratio between the indentation volume and the pile-up effect may then be greatly impacted by the friction coefficient, and should be considered for further investigations.

BIOGRAPHY

Romain Petre-Bordenave is graduate from the ENIT (Ecole Nationale d'Ingénieurs de Tarbes, France) where he obtained his M.Eng. in mechanical engineering. He also obtained a MA in material research from the UPS (Université Paul Sabatier, Toulouse, France). After an internship within the CNES (Centre National d'Etudes Spatiales), he's currently working as research engineer for Fialab, a company that provides failure analysis services.

  This parameter B that we propose to study is obtained by following the same approach than the one developed by Cheng & Cheng in 1998[START_REF] Cheng | Relationships between hardness, elastic modulus, and the work of indentation[END_REF]: , , .

Figure 2 .

 2 Figure 2. Al 2024: Application of the nanovision method on an imprintThis corrected surface was tested under the same conditions as the previous one. The uncertainty has appeared to be reduced down to 10%.

Figure 3 .

 3 Figure 3. Al 2024: comparison of the AFM scan (left), and the embedded scan with subtraction (right)

TABLE I .

 I COMPARISON OF TO VOLUME MEASUREMENTMEANS

Pile-up volume (μm 3 ) AFM Embedded scan with subtraction

	Al 2024	0.61	0.32

a. Example of volume measurement on an Al 2024 sample, the volume measurement difference is up to 50% adding the operator bias


de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Hydrodynamics is a branch of mechanics which studies the motion of fluids. This science is chanced to be fascinating itself and extremely important in practical sense at the same time. For example, one can think about numerous applications ranging from engineering to environmental sciences through oceanography and hydraulics.

Fluid mechanics hase revealed many challenging problems in physics, mathematics (e.g. the famous unsolved question of global well-posedness of 3D Navier-Stokes equations) and scientific computing (development of new performant numerical schemes). Applications permanently give rise to new problems. It clearly indicates that this field of science is far from being finished and there is a permanent demand on specialists able to face these tasks.

The present book should be considered as a first course in fluid dynamics. The comprehension of this text necessitates only the knowledge of basic concepts from continuum mechanics, real and complex analysis. Advantageously, it makes this book accessible to wide range of readers.

The author is a professor in the Department of Aerospace and Mechanical Engineering at Boston University. Professor Howe is not only a confirmed researcher but an excellent pedagogue as well. He succeeded to explain in a comprehensive manner complex topics of hydrodynamics and made the reading a fascinating scientific journey. This book has all the chances to become a classical textbook on this subject.

It is organized as follows. In the first chapter the author presents the governing equations of fluid motion while in the second one he considers a special case of potential flows. Next two chapters deal with ideal flows (two dimensional and rotational, respectively). The chapter five is an elementary introduction to an astonishing topic of surface gravity waves. This book is ended by some basic acoustics.

The reviewer would like to mention one shortcoming. Unfortunately the author does not say anything about numerical methods used in computational fluid dynamics (CFD). We recall that these technics have become the method of reference in industrial applications. Evidently, CFD can be taught further in a separate course, but it is important to mention this subject even at early stages.

In conclusion, Howe's book should by recommended to all students willing to discover the wonderfull world of hydrodynamics. More experienced readers should address more specialized literature.


Georges Repetto
email: georges.repetto@irsn.fr

Christophe Marquié
email: christophe.marquié@irsn.fr

Benoit Bruyère

Tony Glantz
email: tony.glantz@irsn.fr

Benoit

Marquié Ch

CORE COOLABILITY IN LOSS OF COOLANT ACCIDENT: THE COAL EXPERIMENTS

Keywords: Coolability, Blockage, LOCA, Fuel relocation, Reflooding experiments, DRACCAR

d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

During an accident causing the loss of the primary coolant (LOCA), partial or even complete drying of the fuel assemblies may occur. In these conditions, the fuel temperature increase and the coolant pressure drop in the reactor core may lead to significant deformation and rupture of the fuel rod cladding. Fuel fragmentation may occur, leading to fuel relocation within the ballooned area. Depending on the burnup of the fuel rod, extensive fragmentation may also lead to fuel particles dispersal into the coolant through the ruptured cladding. Depending on the size and the distribution of the ballooned areas within the fuel bundle, the cooling flow might be impaired, which may challenge the fuel assembly coolability and, by extension, the core coolability.

The results (Fig. 1), which illustrate this phenomenon, come from an experimental LOCA program performed, in the 1980's by the Institut de Protection et de Sûreté Nucléaire former IRSN [START_REF] Bourdon | Analyses of the Phebus-LOCA tests 215-R and 2018 using FRETA-F V1.1 code NURETH-11[END_REF], in 5x5 bundle including fresh fuel rods. All the LOCA experiments performed with irradiated fuel rods (in particular two examples, at 35 GWd/t for FR2-Germany preformed in 1983 [START_REF] Karb | LWR fuel rod behaviour in the FR2 in-pile tests simulating the heatup phase of a LOCA[END_REF] (Fig. 2a) and at 90 GWd/t, more recently (2006) in Halden-Norway [START_REF] Kekkonen | LOCA testing at Halden, the fourth experiment IFA-650.4[END_REF] (Fig. 2b)) have shown an accumulation of the fragmented fuel pellets in the ballooned region [START_REF]Fuel fragmentation, relocation and dispersal during the loss-of coolant-accident , US-NRC[END_REF]. The resulting increase of the power density in the ballooned area may also affect the core coolability. So, the consequences of both deformations and fuel relocation on the cooling efficiency when reflooding the core by the ECCS (emergency core cooling systems) are important safety issues, and have never been experimented.

The knowledge generated by these new experiments will answer long shared concerns by the international community (such as the effect of fuel relocation in blocked areas in the core), and will allow to validate the DRACCAR code [START_REF] Repetto | DRACCAR, a new 3D-thermal mechanical computer code to simulate LOCA transient on Nuclear Power Plants -Status of the development and the validation[END_REF] developed and used by IRSN to simulate any prototypical LOCA transient. The need of this kind of experiments has been proposed in 2005, in the NURETH11 [START_REF] Grandjean | Coolability of blocked regions in a rod bundle after ballooning under LOCA conditions, Main findings from a review of the past experimental programmes[END_REF].

COOLABILITY OF BLOCKED REGION WITH FUEL RELOCATION

The domestic and international state of the art describing the context and the need of coolability of blocked regions is synthesized in some IRSN publications [START_REF] Bourdon | Analyses of the Phebus-LOCA tests 215-R and 2018 using FRETA-F V1.1 code NURETH-11[END_REF][START_REF] Grandjean | Coolability of blocked regions in a rod bundle after ballooning under LOCA conditions -Main findings from a review of past experimental programmes[END_REF] and internal literature reviews [START_REF] Grandjean | A state-of-the-art review of past programs devoted to fuel behaviour under LOCA conditions: Part One, Clad swelling and rupture -Assembly flow blockage[END_REF][START_REF] Grandjean | A State-of-the-Art Review of Past Programs Devoted to Fuel Behavior under LOCA Conditions. Part Two, Impact of clad swelling upon assembly cooling[END_REF]. The main lessons are summarized below. Based on the previous experimental programs (FEBA [START_REF] Ihle | FEBA Flooding Experiments with Blocked Arrays[END_REF], SEFLEX [START_REF] Ihle | SEFLEX -Fuel Rod Simulator Effects in Flooding Experiments[END_REF], THETIS [START_REF] Pearson | Reflooding Experiments on a 49-Rod Cluster Containing a Long 90% Blockage[END_REF][START_REF] Cooper | Jowitt -The THETIS 80% Blocked Cluster Experiment[END_REF], ACHILLES [START_REF] Denham | ACHILLES Un ballooned Cluster Experiments -Part 1 : Description of the ACHILLES rog, Test section, and Experimental Procedures[END_REF], FLECHT [START_REF] Hochreiter | [END_REF], CEGB [START_REF] Fairbain | Studies on the effects of blockage upon LWR emergency core cooling systems[END_REF]), the experimental conditions, including the characteristics of the blockage (blockage ratio, length of the maximum blocked area, cladding thickness in the ballooned zone.) and the initial thermal hydraulic test conditions, the phenomena listed below have been ranked accordingly to their impact level:

1.

Representativeness of the blockage, 2.

Influence of the blockage ratio, 3.

Influence of the length of the blockage, 4.

Influence of the blockage configuration: coplanar versus non-coplanar, 5.

Influence of the flow bypass, 6.

Influence of the nature of the reflooding: forced versus gravity.

The analysis of these phenomena can specify limits of the blockage coolability in the most penalized geometry (length and rate) and thermal hydraulic conditions. Thus, it seems that the blockages although important, if of moderate length (<100 mm), pose no significant cooling impairment, as one might be tempted to conclude in view of only FEBA [START_REF] Ihle | FEBA Flooding Experiments with Blocked Arrays[END_REF] and SEFLEX [START_REF] Ihle | SEFLEX -Fuel Rod Simulator Effects in Flooding Experiments[END_REF] results, a 90% blocking is always coolable. It was also shown that the maximum ratio of 90% blockage is not necessarily the most case penalizing the cooling if the deformation is axially extended. Regarding CEGB analysis [START_REF] Repetto | DRACCAR, a new 3D-thermal mechanical computer code to simulate LOCA transient on Nuclear Power Plants -Status of the development and the validation[END_REF], a possible impaired coolability has been outlined, in the case of long ballooning with high blockage ratio (>80%). It also follows, from this analysis [START_REF] Grandjean | A State-of-the-Art Review of Past Programs Devoted to Fuel Behavior under LOCA Conditions. Part Two, Impact of clad swelling upon assembly cooling[END_REF], that the understanding of the deformation and rupture mechanisms of the fuel cladding is a fundamental concern: in fact, the deformation and swelling of the claddings are causing the blockage of sub-channels, and cladding rupture freezes this deformation balancing the internal and external pressures of the fuel rod. Therefore, it is first necessary to understand the mechanisms of deformation and fracture (thermal mechanical behavior) to investigate realistically the effects of the blockage on the thermal hydraulic. All the experimental results and the main outcomes regarding cooling of partially blocked assemblies were obtained on out-of-pile tests using bundles with electrically heated "fuel" rods. Since the heating axial profiles of the simulators were uniform and preset, the tests didn't reproduce the impact the fuel relocation in the ballooned areas as observed in the in-pile tests performed on irradiated fuel rods (FR2 [START_REF] Karb | LWR fuel rod behaviour in the FR2 in-pile tests simulating the heatup phase of a LOCA[END_REF] and Halden IFA-650.4 test [START_REF] Kekkonen | LOCA testing at Halden, the fourth experiment IFA-650.4[END_REF]. The fuel fragments relocation results in a local increase of the power density depending on the filling ratio. However, the significant difference between test results comparable to FEBA [START_REF] Ihle | FEBA Flooding Experiments with Blocked Arrays[END_REF] and SEFLEX [START_REF] Ihle | SEFLEX -Fuel Rod Simulator Effects in Flooding Experiments[END_REF] programs suggests [START_REF] Repetto | DRACCAR, a new 3D-thermal mechanical computer code to simulate LOCA transient on Nuclear Power Plants -Status of the development and the validation[END_REF] a strong coupling between the heat source and the deformed claddings, as it may exist in a balloon filled with fragmented relocated fuel; this may significantly deteriorate the cooling of blocked regions. So the configuration of the rods used in the past was not representative of the real situation. Fuel relocation, as observed in several in-pile LOCA tests with irradiated fuel (listed above), and its potential impact on the local cooling of the blocked areas, have to be investigated and properly modelled.

Antagonistic influences due to the presence of a blockage will be evaluated through a semi integral experiment using a 7x7 bundle geometry at the full length scale. On one hand, the reduction of the section between the deformed fuel rods will increase the flow velocity. On the other hand, the flow bypass from the deformed fuel rods in the blocked region to the peripheral intact rods (cross-flow phenomena), will led to a reduction of mass flow in the sub channels of the blockage and therefore the heat transfers. The possible presence of water droplets in the steam flow may modify this trend. Their role in heat transfer is important, whether through the heat extracted at their impact on the walls or via their vaporization in the bulk flow. Due to their inertia, their paths do not necessarily follow that of the steam flow path. More detailed activities foreseen in collaboration with a research laboratory of the Lorraine University (LEMTA) will focus on the characterization of two phase flows with heat transfer in deformed structures at a smaller scale. The work foreseen in this area is described in the more general paper on the PERFROI project [START_REF] Repetto | Core coolability in loss of coolant accident: the PERFROI project[END_REF][START_REF] Repetto | The R&D PERFROI project on Thermal mechanical and thermal hydraulics behaviors of a fuel rod assembly during a Loss Of Coolant Accident[END_REF].

THE COAL EXPERIMENT

The COAL program will concern thermal hydraulics experiments on a bundle of electrically heated rods, with simulation of large blockage and fuel relocation.

The test section and the bundle geometry

The bundle will consist of rods (electrically heated), some with pre-deformed zone with local overheating representing fuel relocation. The test bundle will be made of 49 (7x7) rods (including 16 deformed rods and 33 non deformed rods -Fig. 3a), similar to that of the THETIS [START_REF] Pearson | Reflooding Experiments on a 49-Rod Cluster Containing a Long 90% Blockage[END_REF][START_REF] Cooper | Jowitt -The THETIS 80% Blocked Cluster Experiment[END_REF] tests performed in the past by AEA Winfrith UK in 1983-1984, which will also allow experimental comparisons. This configuration was preferred to that of ACHILLES [START_REF] Denham | ACHILLES Un ballooned Cluster Experiments -Part 1 : Description of the ACHILLES rog, Test section, and Experimental Procedures[END_REF] to limit the number of electrical rods. The COAL bundle will include 3 guide tubes and grids to be as representative as possible of a real PWR fuel bundle. For these experiments, the cladding of the electrical rods was proposed to be constructed with Hastalloy material to prevent oxidation. To avoid any chemical interaction, the grids should be in Inconel alloy. It was initially foreseen to cut a real Inconel PWR (17x17) grid for the COAL grid (7 x 7) test section, we added 4 guide tube positions (Fig. 3b). So the presence of guide tubes will increase the representatives of the thermal hydraulics behavior for the reactor case: there are will also necessary for instrumentation and of course, mechanical reason. Nevertheless, it was decided to suppress the guide tube in the deformed area to facilitate the analyses of the results. The chosen configuration is illustrated in Fig. 3c). Inconel PWR grids are no more available, so a specific fabrication for the COAL bundle has been launched with a design including mixing vanes that would have an effect of thermal hydraulic behavior. The heating zone is about 3 m hight (close to the real PWR geometry) and roughly 100 mm in diameter. It should be noted that COAL is a program to be conducted in an existing ad -hoc thermal hydraulics facility (cf section 3.3).

The SAFRAN electrical prototype rod

The first step was to develop a prototype of the electrically heated test rod with a local overheated balloon (so-called SAFRAN electrical rod -Fig. 4). The main technical difficulties identified at this stage are related to the manufacturing of the test rods, including an adapted instrumentation operational at high temperature and high pressure (3 MPa). SAFRAN is a real technological challenge, i.e. besides obtaining a representative tube geometry (Fig. 4a), the following constraints have been added: technique should allow extended test rods manufacturing at a reasonable cost, thermocouples to be welded on the outer surface of the cladding and the resistor should survive multiple cycles in corrosive steam above 1000°C and several quench phases. The validation of the process of the pre deformed balloon (Fig. 4b) has been done in 2013.

Intact rod (by passs) Guide tube Pre deformed rod

Pre-deformed cladding

During the qualification performed in 2014 on small scale SAFRAN rods (300 mm with a 50mm for the hottest zone), different kinds of resistors (3), insulators (1) and configuration of the heaters have been tested and allow the final design (Fig. 5a) of the electrical rods for the COAL bundle. Specific care has been taking to be as much as possible representative * of the thermal conductance of the UO 2 providing the residual power to the cladding: so aluminia balls (Fig. 5b-1 or 5c) or compacted powder are possible, according to the rod provider, to represent the debris inside the ballooning. The thermal impact of the two solutions is weak according to DRACCAR evaluations. The design of the test section, including the instrumentation, is in progress: the construction of the first bundle is foreseen by the end of 2016. This test section will be inserted in an out of pile thermal hydraulics loop which can simulate the reflooding phase of a prototypical LOCA transient (cf. following section).

The thermal hydraulic loop

COAL experiments will be performed in the AREVA BENSON facility at Erlangen (in Germany) which allows running high pressure tests to 3 MPa (30 bar). This facility is operating since roughly 40 years for different kinds of experiments in the thermal hydraulic field [START_REF] Schmidt | High-Pressure Test Facility -25 Years of Operation[END_REF]. The work will proceed in two steps:

1. Qualification tests will be performed by the end of 2016 on a bundle with non-deformed heated rods. These tests will be used as a reference tests in order to qualify all the experimental process and to compare with already performed experiments such as PERICLES * * * * , 2. Then tests with heated pre-deformed simulators, including local overheating of the balloon regions, will be performed from 2017 up to 2019. Three series of tests are planned with different flow blockage ratios or ballooning lengths (cf. section 3.5). In each series, the effects of thermal hydraulic parameters (cf. section 3.4) will be carefully investigated. The third campaign is optional and depends on the results of the previous campaigns. 3. Finally, all the tests will be analyzed and interpreted. The objective is to validate a heat transfer model adapted to bundle conditions, to be implemented in DRACCAR code [START_REF] Bascou | Computational Analysis of Multi-pin Ballooning during LOCA and Post LOCA Transient using the Multi-physics Code DRACCAR[END_REF].

The experimental parameters of the test campaigns will be defined in order to investigate the bundle geometry related phenomena (blockage ratio, balloons lengths) and the thermal hydraulic related phenomena (local overheating of the balloons, injected water temperature, coolant flow rate and system pressure levels and kinetics to simulate various break sizes).

The scenario and the thermal hydraulic test parameter

The scenario is divided in two phases as classical "Reflooding experiments" already performed in the 80's such as FEBA for example: 1. Heat up phase in dry steam atmosphere, 2. Reflooding by water injection with thermal hydraulic conditions.

The main thermal hydraulics parameters foreseen are in the range below:

• inlet water flow velocity : 1 to 8 cm/s, • coolant pressure : 0.1 to 3 MPa (30 bar).

An example of scenario is illustrated in Fig. 8, showing a comparison of FEBA reflooding experimental results compared to DRACCAR [START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF] and CATHARE calculations [START_REF] Geffraye | CATHARE 2 V2.5_2: A Single Version for Various Applications[END_REF]. It's not the objective of the paper but the post-test calculation has been improved using DRACCAR compared to CATHARE. Others parameters (flow blockage -ratio and length of the deformed area) will be defined based on thermal hydraulics parametric studies. There are proposed in the following section.

Water injection

The geometrical parameters (blockage area)

The blockage region is foreseen to be located in the middle position (Fig. 9 a) with a cosine power (P) profile (Fig. 9c). Table III gives the configuration chosen for different blockage areas: for the first deformed bundle, the nominal blockage ratio should be 80% with a maximal deformation height of 100 mm (with170 mm for the total height of the ballooning taking into account the up and down stream interfaces with the nominal diameter : Fig. 9b). The geometry of the second bundle corresponds to a so called long ballooning situation. For bundles 1 and 2, the balloons are coplanar. The idea is to progressively increase the total pressure drop of the blockage. For the optional configuration we have proposed a reduction of blockage ratio (down to 61% which corresponds to state of the beginning of the contact between fuel rods) or a non coplanarity of the balloons (blockage at different elevations). The propositions will be representative of a significant blockage zone for 3 ratios: 61%, 80 and 90%, which have been really observed in particular in the Phebus LOCA experiments (from Fig. 1).

61% (first contact)

THE PRELIMINARY PRECALCULATION USING DRACCAR CODE

The simulation tool DRACCAR [START_REF] Repetto | DRACCAR, a new 3D-thermal mechanical computer code to simulate LOCA transient on Nuclear Power Plants -Status of the development and the validation[END_REF][START_REF] Bascou | Computational Analysis of Multi-pin Ballooning during LOCA and Post LOCA Transient using the Multi-physics Code DRACCAR[END_REF][START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF][START_REF] Ricaud | Multi-pin Ballooning during LOCA transient: A Three Dimensional Analysis[END_REF], developed by IRSN, with the support of EDF, is at this stage, used to define some parameters of the experiments such as the blocked bundles geometry, the heatup scenario of the bundles or the test matrix. Then DRACCAR will be used to perform the pre-calculation of all the tests foreseen in COAL experiment.

Brief description of the code

DRACCAR is a simulation tool for fuel assembly mechanical behavior and coolability assessment during a LOCA transient. Its aim is to simulate the 3D thermomechanical deformation and reflooding of a fuel rod assembly including its coolability as well as structure embrittlement.

The DRACCAR code is based on a 3D non-structured meshing able to model a simple fuel rod, a partial or a full assembly, as well as a surrounding shroud. It is based on an axial discretization of the rod which leads to analyze quasi-independent 2D thermal mechanical problems. Important modeling such as pellet eccentricity, heat transfers (within the solid and through the fluid) or material properties evolutions (oxidation layer, phase changing,...) can thus be taken into account and the cladding integrity during a LOCA transient can be addressed even in case of contact between the structural elements. In that case, the geometry is strongly changed (flattened zone contact) as well as the loading nature (mixed stressdisplacement loading) and so the rupture is more difficult to model than a threshold criteria used in most of the multi-rod codes: with DRACCAR, nonlinear geometrical effects are added to non-linear behaviour laws in the modeling. Also important is the possibility to get a better knowledge on the system's capability to cool structures whatever are the evolutions of the deformation of the rods and the blockage of the sub-channels. Obviously these two critical issues which are essential to treat in modeling LOCA transient effects, can only be dealt with in a realistic manner with a multi-pin code coupled to an efficient 3D thermal hydraulics code, and that's why DRACCAR is currently coupled to the two phase flow module CESAR of the ASTEC code [START_REF] Tregoures | Reactor Cooling Systems Assessment of the ASTEC V1.3 code in Support to the French IRSN PSA-2 on the 1300MWe PWR[END_REF], able to compute deformed geometry evolutions thus actualizing the coolant flow passage within the different sub-channels.

Many results have already been obtained with the DRACCAR code with respect to a substantial validation matrix (e.g. FEBA [START_REF] Ihle | FEBA Flooding Experiments with Blocked Arrays[END_REF][START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF], HALDEN IFA 650 [START_REF]Benchmark calculation on HALDEN IFA 650 LOCA tests results[END_REF], PERICLES [START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF], PHEBUS 218 [START_REF] Scott De Martinville | ISP-19 Behaviour of a fuel rod bundle during a large break LOCA transient with a two-peaks temperature history (Phebus experiment) -Final Comparison report[END_REF], REBEKA 6 [START_REF] Karwat | ISP-14 Behaviour of a Fuel Bundle Simulator during a specified Heat-up and Flooding Period (REBEKA experiments) -Final Comparison Report[END_REF], ROSCO [START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF], SEFLEX [START_REF] Ihle | SEFLEX -Fuel Rod Simulator Effects in Flooding Experiments[END_REF][START_REF] Bascou | Oxygen diffusion and partially blocked bundle reflooding simulation using DRACCAR[END_REF] experiments) in the field of a LOCA type transient.

DRACCAR modeling of COAL experiment.

The bundle is simulated on a height equivalent to the rods heating length, with the square housing (metallic shroud in the same material as the cladding). One boundary condition at the inlet and one at the outlet of this portion close the system. The intact bundle is composed of 46 electrical rods and 3 guide tubes. The ballooned bundles included 16 rods with a local swelling. In the balloon, the fuel fragment is simulated by a porous material which has a density and conductivity close to those of the UO 2 pellet. Taking into account the symmetry of the test sections, half a bundle is modeled (Fig. 10). Several rods deformations have been tested with DRACCAR, the one presented in Fig. 10b is composed of balloons that have a height of 100 mm and are all positioned at the same elevation at the middle of the bundle, leading to a 90% blockage of the test section. The axial power profile imposed in the intact rods has a cosine shape (Fig. 11a). The relocation in the balloon has been simulated by setting a specific axial power profile in the ballooned rods (Fig. 11b). This last power profile has been determined by a DRACCAR calculation of fuel relocation in a pre-deformed rod. The axial meshing takes into account the axial power profile discretization and the balloon geometries. The meshes height never exceeds 100mm (smaller in the ballooned area). Six Grids are taken into account by setting a singular pressure loss at their positions. 10b is composed of balloons that have a height of 100 mm and are all positioned at the same elevation at the middle of the bundle, leading to a 90% blockage of the test section. The axial power profile imposed in the intact rods has a cosine shape (Fig. 11a). The relocation in the balloon has been simulated by setting a specific axial power profile in the ballooned rods (Fig. 11b). This last power profile has been determined by a DRACCAR calculation of fuel relocation in a pre-deformed rod. The axial meshing takes into account the axial power profile discretization and the balloon geometries. The meshes height never exceeds 100mm (smaller in the ballooned area). Six Grids are taken into account by setting a singular pressure loss at their positions.

Deformed rod Guide Tube Intact rod shroud

A typical COAL test will be separated into two phases (section 3.4), the first one dedicated to the heat-up of the test section and the second to the reflooding. The housing or shroud has to be at a temperature close to the rods temperature at the end of the first phase; otherwise it would create a cold spot in the test section which would disturb the reflooding. As a consequence, the housing or shroud has to be heated. The main issue is that the housing doesn't heat-up at the same rate as the rods.

Several DRACCAR calculations have been performed to define a heat-up phase allowing to obtain a temperature of the shroud and the adjacent rods as close as possible before the reflooding. As a consequence, the test section is first heated up by steam. Then, only the shroud (housing) heating is performed and finally rods are heated-up. Figure 12 presents a DRACCAR simulation of the heat-up phase of the COAL intact bundle.

Figure 12. Heat-up phase of a COAL test

The heat up phase will lasted less than 10 minutes, before the water injection. The total duration of a COAL experiment would be less than ½ hour in order to perform numerous transient during one day (Target : 4 experiments a day in order to study numerous thermalhydraulics conditions which seems to be very challenging).

DRACCAR preliminary results

Several reflooding pre-calculations have been performed with the DRACCAR code. Figure 13 illustrates preliminary DRACCAR calculations for the intact bundle geometry for two thermal hydraulics conditions representative of large break LOCA reflooding (at 3bar) and for intermediate break LOCA (25 bar). In these cases, all the clad reached almost the same maximum temperature around 650/700°C, after water injection for a temperature threshold value at 600°C.

In case of thermal-hydraulics conditions representative of an intermediate break LOCA, the code predicts the coolability of a 90% blocked bundle with short length for the ballooning. For high pressure (25 bar), the quenching of the bundle appears more rapidly compared to the thermal-hydraulic conditions representative of a large break LOCA (low pressure at 3 bar). Figure 14 illustrates calculations for the deformed bundle geometry for the two above thermal hydraulics conditions. The results outlined different behavior regarding the blocked area with an increase of the peak cladding temperature (PCT) of about 200°C for the low pressure configuration (650 to 850°C). Again, the reflooding appears to be more efficient at high pressure, limiting the PCT at about 800°C. The temperature stabilized after the reflooding (Fig. 14a) for the blockage region is under investigation. Experimental results are now needed to confirm the behavior predicted by the code and to validate the model implemented in DRACCAR.

The COAL tests matrix will cover the thermal-hydraulic conditions characteristics of a large break LOCA and those of an intermediate break LOCA. As far as possible, the same test conditions will be applied on the intact bundle and on the ballooned bundles, to be able to compare the impact of the blocked area with large ballooning on the fuel cladding.

CONCLUSION

Many experiments have been performed in the field of ballooned fuel bundle refloodind (FEBA, SEFLEX, THETIS, ACHILLES, FLECHT, CEGB), nevertheless, IRSN considers that the configurations

Guide Tube

Outer Rod

Outer Rod Inner Rod Shroud used for the electrical rods were not representative of the real situation, in particular the fuel relocation (and the right thermal transfer of the heat from the heaters to the cladding) that may occur in case of irradiated fuel rods.

This paper presents the new COAL experiments on the reflooding of a deformed fuel bundle with simulation of the fuel fragments relocation inside the balloons. We have described the test section, the thermal hydraulics parameters for the experiments and some pre-calculations using DRACCAR code developed by IRSN, in order to prepare the experiments. The results of these experiments will help to refine and validate the heat exchange models implemented in the code studying the reflooding and the behavior of the code in the above configuration.

In addition to COAL experiments, it is foreseen to perform specific separate-effect-tests at the subchannel scale [START_REF] Repetto | The R&D PERFROI project on Thermal mechanical and thermal hydraulics behaviors of a fuel rod assembly during a Loss Of Coolant Accident[END_REF] in order to improve our understanding on different processes involved in the reflooding of a deformed fuel assembly, which is not possible to get from an integral experiment.

NOMENCLATURE

Figure 1 . 2 .

 12 Figure 1. Bundle of deformed fuel rod Figure 2. Fuel relocation in the ballooned area Phebus LOCA experiments (1983) a) FR2 Fuel rods fresh or irradiated b) Halden test (2006)

Figure 3 .

 3 Typical bundle fuel rods for COAL experiments

Figure 4 .

 4 Figure 4. Electrical deformed fuel rod prototype (SAFRAN)

Figure 5 .

 5 Figure 5. Detail of the design of rod prototype (SAFRAN)

Figure 6 Figure 6 .Figure 7 .

 667 Figure 6. COAL test bundle and circuit of the BENSON facility

Figure 8 .

 8 Figure 8. FEBA experiment: test results and simulation.The range of the thermal hydraulics parameters (Tab. I) that should be tested is provided by results of CATHARE calculations for different break sizes (3 to 14 inches).

Figure 9 .

 9 Axial position of the blockage area

Figure 10 .

 10 DRACCAR simulation of different bundlesSeveral rods deformations have been tested with DRACCAR, the one presented in Fig.

Figure 11 .

 11 Figure 11. Axial linear power profile of rods for intact rods a) and b) for ballooned rods with simulation of fuel fragments relocation

Figure 13 .

 13 DRACCAR preliminary Calculations for intact bundle geometry -Clad temperature evolution at 1.5 m for intact bundle geometry for a) Large break LOCA reflooding (3bar) and b) for Intermediate break LOCA (25 bar).

Figure 14 .

 14 DRACCAR preliminary Calculations for deformed bundle geometry -Clad temperature evolution at 1.5 m for intact bundle geometry for a) Large break LOCA reflooding (3bar) and b) for Intermediate break LOCA (25 bar).

Table I . Thermal hydraulic conditions during Reflooding scenario T/H parameters Intermediate Break LOCA Large Break LOCA

 I

	Pressure	2 to 6 MPa (60 bar)	0.1 to 0.5 MPa (5 bar)
	Cladding Temperature before Reflooding	500 to 600°C	600 to 800°C
	Inlet mass flow rate	2 to 25 kg/m²/s	20 to 30 kg/m²/s
	Water temperature (under satured conditions)	0°C to 25°C	20 to 30°C
	Power by fuel rod	1.5 to 3.0 kW	3.0 to 5.0 kW
	The test matrices of those experiments (in progress) will take into account the possibilities of the
	BENSON loop (Tab. II).
	Table II. Thermal hydraulic conditions for the BENSON loop
	T/H parameters		Range of the possible values
	Pressure		0.15 to 3 MPa (30 bar)
	Cladding Temperature before Reflooding	500 to 700°C
	Inlet mass flow rate		0 to 50 kg/m²/s
	Water temperature (under saturated conditions)	Few degrees to 40°C

Table III . Preliminary proposition for the geometrical parameters Parameters Bundle 1 Bundle 2 Bundle 3a* Bundle 3b*

 III

	Blockage ratio (symmetric) and rod shape	80 %	90%	61%	90%
	Total height of the ballooning area	170 mm	370 mm	370 mm	370 mm
	Height of the maximal deformation (P x 2)	100 mm	300 mm	100 mm	300 mm
	Coplanarity of the balloon	Yes	Yes	Yes	No

*options (not yet defined)

ACKNOWLEDGMENTS

This work is completed within the framework of RSNR Project from a French State aid managed by the National Agency of Research under the program of Investments for the Future carrying the reference n° ANR-11-RSNR-0017. Particular acknowledgments are also given to EDF for its financial support.


Georges Repetto
email: georges.repetto@irsn.fr

Cristina Dominguez
email: cristina.dominguez@irsn.fr

Benoît Durville
email: benoit.durville@irsn.fr

Stéphane Carnemolla

Damien Campello
email: damien.campello@insa-lyon.fr

Nicolas Tardif
email: nicolas.tardif@insa-lyon.fr

Michel Gradeck
email: michel.gradeck@univ-lorraine.fr

THE R&D PERFROI PROJECT ON THERMAL MECHANICAL AND THERMAL HYDRAULICS BEHAVIORS OF A FUEL ROD ASSEMBLY DURING A LOSS OF COOLANT ACCIDENT

Keywords: Coolability, LOCA, cladding deformation, rupture, fuel relocation. * Characterisation and Investigation for Improved Calculation

d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION AND CONTEXT OF THE PROJECT

During an accident causing the loss of the primary coolant (LOCA), partial or even complete drying of the fuel assemblies may occur. In these conditions, the fuel temperature increase and the coolant pressure drop in the reactor core may lead to significant deformation and rupture of the fuel rod cladding. Fuel fragmentation may occur, leading to fuel relocation within the ballooned area. Depending on the burnup of the fuel rod, extensive fragmentation may also lead to fuel particles dispersal into the coolant through the ruptured cladding. Depending on the size and the distribution of the ballooned areas within the fuel bundle, the cooling flow might be impaired, which may challenge the fuel assembly coolability and, by extension, the core coolability. The results (Fig. 1), which illustrate this phenomenon (deformation of a fuel rod assembly), come, in particular but not only, from an experimental LOCA program performed, in the 1980's by the Institut de Protection et de Sûreté Nucléaire former IRSN (LOCA test 215-R [START_REF] Repetto | Final Experimental Report, Phebus LOCA Test 215-R[END_REF] and reported in [START_REF] Bourdon | Analyses of the Phebus-LOCA tests 215-R and 2018 using FRETA-F V1.1 code[END_REF]), in 5x5 bundle including fresh fuel rods. All the LOCA experiments performed with irradiated fuel rods have shown fuel relocation [START_REF]Fuel fragmentation, relocation and dispersal during the loss-of coolant-accident , US-NRC[END_REF]. Figure 2 gives an example for FR2-Germany [START_REF] Karb | LWR fuel rod behaviour in the FR2 in-pile tests simulating the heat up phase of a LOCA[END_REF] at burn up about 35 GWd/t. The resulting increase of the power density in the balloonned area may also affect the core coolability. The consequences of deformations and fuel relocation on the cooling efficiency when reflooding the core by the ECCS (emergency core cooling systems) are important safety issues. Fuel relocation, as observed in several in-pile LOCA tests with irradiated fuel and its potential impact on the local cooling of the blocked areas, have to be investigated and properly modeled.

The proposed research program is based on a state of the art review of the available experimental results.

The knowledge generated by this new project will answer long shared concerns by the international community (such as the effect of fuel relocation in blocked areas in the core), and will allow to validate the DRACCAR code [START_REF] Repetto | DRACCAR, a new 3D-thermal mechanical computer code to simulate LOCA transient on Nuclear Power Plants -Status of the development and the validation[END_REF] developed and used by IRSN to simulate any prototypical LOCA transient.

From a regulatory point of view, maintaining the short and long term core coolability is the primary requirement. More specifically, to fulfill this requirement, two criteria, which are calculable and representative of the expected physical phenomena related parameters, are usually taken into account: the Equivalent Cladding Reacted (ECR) and the maximum temperature of the cladding. The regulations often require these two values must not exceed a specific threshold during a prototypical LOCA transient.

Compliance with these criteria is obtained through adapted methodologies and advanced simulation tools (carefully validated on specific experimental results).

As in other countries, LOCA rulemaking changes have been initiated in France to account for recent experimental results (impact of burn up on the LOCA limits, effect of fuel relocation on the peak cladding temperature, etc..) and to account for the fact that the current fuels are irradiated in more challenging operating conditions than in the 1970's when the former LOCA limits had been defined. IRSN has produced a state of the art review of the R&D programs conducted during the last thirty years, especially the swelling and the rupture of the cladding [START_REF] Grandjean | A state-of-the-art review of past programs devoted to fuel behaviour under LOCA conditions: Part One, Clad swelling and rupture -Assembly flow blockage[END_REF], the impact of the fuel deformation on the cooling of fuel assemblies [START_REF] Grandjean | A State-of-the-Art Review of Past Programs Devoted to Fuel Behavior under LOCA Conditions. Part Two, Impact of clad swelling upon assembly cooling[END_REF], the oxidation/hydriding and the mechanical resistance of the cladding during quench and post-quench loads [START_REF] Grandjean | A State-of-the-Art Review of Past Programs Devoted to Fuel Behavior under LOCA Conditions. Part three, cladding oxidation, resistance to quench and post quench loads[END_REF]. This synthesis is the basis of the State Of the Art Report on LOCA [START_REF]Nuclear Fuel Behavior in Loss-of-coolant Accident (LOCA) Conditions: State-of-the-art Report[END_REF]) showed the need of further experiments and identified three important issues (or pending questions) that must be addressed:

• What is the maximum ratio of blockage that can result from a LOCA and is the core still coolable with such a flow blockage?

• When and how the fuel fragments relocate in the ballooned areas? What is the impact of fuel relocation on the peak cladding temperature (PCT) and on the maximum oxidation rate?

• During and after the reflooding of the core, how to demonstrate long term coolability, taking into account base irradiation, transient oxidation and hydrogen pick up?

An R&D program (CYCLADES * * * * [START_REF] Barré | Micaelli -Fuel R&D Needs and Strategy towards a Revision of Acceptance Criteria[END_REF]) was launched by IRSN with the support of EDF to provide answers to these three questions. This program includes both experimental activities and software development for simulation (DRACCAR [11 and 12]).

The PERFROI project proposes to answer the first question above. In scientific terms, the project aims firstly to quantify the thermal mechanical evolution of cladding in some specific configurations such as those involving contact between fuel rods or significant temperature gradients in the fuel rod environment, and to quantify the impact of fragmented fuel rods relocation in the balloon on cooling of the fuel assemblies during the reflooding. Specific research aims to study heat exchanges occurring between the walls of the deformed cladding and the two-phase flow in fog form (i.e. steam plus droplets); these heat exchanges conditioning temperature change in a fuel assembly. Antagonist influences due to the presence of a blockage will be evaluated. These influences result from the following physical phenomena:

• The flow bypass of the blocked region, due to the reduction of the section between the deformed fuel rods, leading to a reduction of mass flow in the sub channels of the blockage. This reduction limits the flow of the cooling capacity. • The presence of water droplets in the steam flow may modify this trend. Their role in heat transfer is important, whether through the heat extracted at their impact on the walls or via their vaporization in the bulk flow. Due to their inertia, their paths do not necessarily follow that of the steam flow path.

STRUCTURE OF THE PERFROI PROJECT

As the need for further studies on two types of phenomena (mechanics and thermal hydraulics) has been shown above, the PERFROI project [START_REF] Repetto | Core coolability in loss of coolant accident: the PERFROI project[END_REF] has been structured in two axes: Axis 1: thermal mechanical studies of the deformation and failure of fuel rods in LOCA conditions taking into account the effect of contact between rods and the effect of an azimuthal temperature gradient. The models or correlations describing the creep laws and rupture criteria from the results of these tests will be integrated in the DRACCAR software, for the assessment of the fuel assembly deformation.

The works that will be achieved in this axis are:

• Perform thermal mechanical creep and rupture tests. The main objective of these parametric tests (ELFE program - §3.1) is to assess the thermal mechanical properties of the cladding which will be used in the COCAGNE tests program ( §3.2); • Investigate the thermal mechanical swelling of cladding tubes simulating multi-rods configuration.

This configuration (COCAGNE test program), never studied experimentally up to now, will provide us new insights regarding balloons formation before and after contact between adjacent rods. It will also quantify the effect of azimuthal temperature gradients; • Define a cladding creep rupture criterion valid for multi-rods conditions, to be implemented in the DRACCAR code (Current criteria are based on single rod tests); • Validate models against the results of these tests.

Small scale experiments at the "LaMCoS" research laboratory (INSA-Lyon) will focus on analysis of the hydrogen behavior in cladding alloys and its impact on the mechanical behavior of the fuel rod ( §3.3).

Axis 2: thermal hydraulics behavior of a partially blocked core zone during the reflooding phase.

The works that will be achieved in this axis concern both semi-integral experiments and experiments at smaller sub-channel scale:

• Thermal hydraulic experiments will be performed in an out-of pile loop (COAL tests program ( §4.1), including a bundle of electrical rods whose deformed areas are locally overheated to simulate the fuel fragments relocation. The results of these experiments will help to refine and validate the heat exchange models used in DRACCAR multi-physics code during the reflooding phases. • More detailed activities on thermal hydraulic foreseen in collaboration with the LEMTA-Nancy research laboratory (University of Lorraine) will focus on the characterization of two phase flows with heat transfer in deformed structures ( §4.2).

AXIS 1 :THERMAL MECHANICAL ACTIVITIES

ELFE experiments

The ELFE experimental results will permit to obtain the creep laws and the rupture criteria for different cladding materials useful for DRACCAR code input, but also to interpret the result of the upcoming COCAGNE experiments ( § 3.2). ELFE experiments are performed in the FIGARO furnace (Fig. 3a) where the test section (Fig. 3b) is heated at high temperature up to 1000°C. Those separate effect experiments are carried on 6 or 9 cm long samples (Fig. 3c).

Different zirconium alloys will be tested with different initial conditions: Alloys: Zry-4, M5 Figure 6 shows the evolution of Fe distribution (or distribution of the phases) with hold time at 850°C. At the beginning of the temperature plateau, both phases cannot be clearly distinguished. As the hold time increases, a small volume fraction of β phase can be observed at the α-grain boundaries.

COCAGNE experiments

The objective of these experiments (constituting the second part of the thermal mechanical axis of PERFROI) is to get precise knowledge of the three-dimensional mechanical behaviour creep of pressurized rod surrounded by structures simulating four neighbouring fuel rods to obtain a geometrical and thermal representative environment. Current criteria are based on single rod tests, and the possible effect of contacts between fuel rods (as observed in Phebus LOCA experiments Fig. 7a) will thus be taken into account resulting in new failure criteria. Experimental data will be compared with three-dimensional thermal mechanical models (Fig. The COCAGNE test rods will be 600 mm long to represent the interval between two grids. It will be linked to a dedicated helium skid regulating its internal pressure up to 180 bar. Its external surface will be either under vacuum or into inert gas at atmospheric pressure, to exclude zirconium oxidation, for technical and safety reasons.

Neighboring rods Guard

Measurements Internal pressurization up to 200 bar

The adjustable position and geometry of the peripheral rods (Fig. 9) have been chosen to simulate as accurately as possible the major types of contact related to loss of coolant conditions, such as guide tube presence for instance. The cladding tube is simultaneously pressurized and heated (direct Joule effect). Reaching the creeping field, a hot spot will initiate ballooning leading quickly to a contact with one or more adjacent heated guards (as well heated through direct Joule effect). To achieve the thermal homogeneity imposed on the sample (∆T = 5 to 10°C), thermal leaks should be minimized. Two main types of tests are foreseen: isothermal tests between 300 and 1100°C and linear ramp tests up to 20K/s. For the temperature increase, the Joule effect direct heating process has been chosen using 5 resistors for 1 rod and 4 guards. Particular attention is paid to the development of the instrumentation of these tests:

• On-line temperature measurement along three perpendicular generating lines of the clad with an uncertainty lower than 10°C despite neighboring rods disturbance, • On-line radial deformation along the same three generating lines, • On-line measurement of the differential pressure applied to the cladding, • Detection of the instant and location of each contact between the sample and its surroundings.

The technological challenge is the following: precision on the measured temperatures should be close to ± 5°C at 1000°C for ramps of about 20 K/s, on a length of 600 mm.

• Thermocouples are intrusive and just give point information. To increase the number of experimental points, IRSN developed a fast moving platform shifting UV pyrometers and laser telemetry sensors along the sample and away from the oven. Each point is scanned at high frequency, resulting in three generating lines temperature and deformation data, updated once per second. • Standard infrared pyrometers do not meet these objectives, mainly because of the perturbing radiative fluxes: photons emitted by the guards and reflected by the sample lead to overestimate its true temperature. To address this issue, IRSN has developed with a supplier innovative UVpyrometers (Ultra Violet), less sensible to these reflections.

Temperature measurement (objective of 1000± 5°C) After the qualification tests, it appears that the use of the monochromatic pyrometry in the infrared range is not possible for the tests with guards. However, 4 monochromatic (IR) pyrometer will be used for the tests on the sample alone, because it gave a satisfying global two sigma uncertainty of ±2,8°C in these conditions.. The pyrometers in the ultraviolet range, tested early 2014, have proved encouraging results with heated guards: the errors (always positive) should be between 7°C at 700°C and 4,5°C at 1100°C, assuming a guard temperature slightly lower than that of the sample (20°C less). The design of pyrometers was improved: sensor mass and sampling time reduction for moving implementation, optic lenses and wavelength choice to fit our geometrical and emissivity conditions. Because of poor photon energy on the UV range, the weak point of this technology is to receive enough signal to start measures: 700°C would be the lower range limit. Deformation measurement (objective of ±100 µm) Regarding the measure of deformation using laser triangulation technic, the preliminary test campaign allowed to verify that the chosen sensor met the requirements of COCAGNE (accuracy of ±16 µm) even on a high temperature target (1200°C) and without disturbing the pyrometers. Measurement of the contact This original use of the ultrasonic properties into metallic components is derived from a former concept of ultrasonic thermometer already used over 2000°C. During the qualification test of this measure on a cold bench, the performances were good enough for the detection of the first contact even for a very light contact pressure and size (starting from 2600 Pascal and 3 mm²). The contact exact time can be determined by data post processing with a precision of at least 50 ms.

Four independent and synchronized systems will be implanted on the four guards. One or several guards in contact will thus be perceptible. The uncertainty of the measurement of the position of the first contact was ± 5mm. An optional post processing result of these sensors is to describe the contact evolution of the ballooned cladding developing against the guard surface. The uncertainty of this measurement is unfortunately difficult to assess in view of the systematic errors observed, influenced by the arbitrary contact pressure. As order of magnitude, on the cold bench, a balloon contact surface exceeding 20 mm can be estimated with errors ranged between 2 and 12 mm. Shorter stretch could not be differentiate from punctual contact. Further development and qualifications are in progress on this subject before COCAGNE facility set up.

Specific research on cladding behavior

In the frame of the thermal mechanical axis 1, specific research at INSA Lyon (LaMCoS -Mechanics of Contact and Structures Laboratory) will focus on in-depth analysis of the hydrogen behavior in cladding alloys and its interaction with the fuel rod mechanical behavior through a PhD position (2014-2016). Hydrogen, due to "hydriding", has been recognized to modify the mechanical behavior of zirconium alloys fuel cladding. Specimens are cut off from an as-fabricated Zy-4 cladding by electro discharge machining. They are 90mm long, 0,57mm thick and their outer radius is 4,75 mm. The experimental setup heats-up a 20mm long length, considered as gage length, by induction heating. Internal pressure and axial force are set in order to produce a uniaxial stress state in the hoop direction. The tests are carried out under inert atmosphere (argon). In addition to the usual measurements (type K-thermocouples, force, pressure), the experimental device is upgraded in order to enable optical full field measurements (Fig. 10 -left) of both displacement and temperature. The thermal field (Fig. 11 c) is measured by an infrared camera. The strain state (Fig. 11 a) is measured by 2D digital image correlation (FE-DIC code developed at the LaMCoS) for strain limited to some percent using high temperature paints to create a grayscale pattern. Then contour detection process [START_REF] Réthoré | Curve and boundaries measurement using B-splines and virtual images[END_REF] is used for finite strain when ballooning and speckle damaging prevent using 2D-DIC. The new setup includes 4 cameras and an infrared camera distributed over the circumference. Full field measurements enable to correlate a 20 degrees temperature evolution over the axial direction with the strain rate gradient in the region of interest (between the coils). The secondary creep is then identified using a simple multiplicative law:

m c r n V M t ε = A × σ × m (1)
Where c r ε is the creep strain, V M σ the Von Mises stress and t the creep time. A, m and n are the three parameters to be determined for each investigated temperature.

Additional information and more detailed results can be founded in [START_REF] Campello | Thermo mechanical behavior of fresh zircaloy-4 under LOCA conditions[END_REF].

AXIS 2 :THERMAL HYDRAULICS ACTIVITIES

The COAL experiments

The objective of the COAL experiments is improve the knowledge and the modeling of reflooding process of a fuel-rod assembly with large blocked area with relocated fuel simulation in the balloons:

1. The first phase was to design and to test an electrically heated rod with pre-ballooned area (SAFRAN prototype : SimulAted Fuel Rod under locA conditioN); 2. The second phase will consist of reflooding tests with roughly full-length bundles in an out-ofpile water loop with adequate characteristics.

This program (COolability of a fuel Assembly during Loca) is detailed in [START_REF] Repetto | Core coolability in Loss Of Coolant Accident: the COAL experiments[END_REF].

Thermal hydraulics experiments performed at sub-channel scale

Within the frame of this thermal hydraulic axis, research is foreseen at the Laboratory for Energy, Theoretical and Applied Mechanics-LEMTA-University of Lorraine. It will focus on the characterization of two-phase flow with heat transfer in the deformed structures [START_REF] Ruyer | Thermal hydraulic across a partially damaged core during the reflood phase of a LOCA[END_REF] (Fig. 12). This will consist in performing specific separate effect tests at the sub-channel scale (channel between fluid and rods). The proposed approach is expected to validate the models already developed on flow and heat transfer between wall and fluid [START_REF] Gradeck | Estimation du transfert de chaleur gouttes/paroi en situation d'APRP pour un REP[END_REF][START_REF] Lelong | Dynamic behaviour of droplet bouncing onto hot slab[END_REF]. Realization and interpretation of these tests will be part of a PhD thesis (2015-2018).It is also planned to conduct a study of the so-called "quench front propagation" area with the aim to better model its dynamics, especially the generation of droplets and their transport by the vapour flow. This will be done as part of a post-doctoral research project.

Local phenomena involved in the process [START_REF] Ruyer | Thermal hydraulic across a partially damaged core during the reflood phase of a LOCA[END_REF] are illustrated in the Fig. 12. As it can be seen on this figure, the two-phase flow occurring in the ballooned region is a mist flow (dispersed water droplet in steam). In previous works [START_REF] Ruyer | Thermal hydraulic across a partially damaged core during the reflood phase of a LOCA[END_REF][START_REF] Gradeck | Estimation du transfert de chaleur gouttes/paroi en situation d'APRP pour un REP[END_REF][START_REF] Lelong | Dynamic behaviour of droplet bouncing onto hot slab[END_REF][START_REF] Gradeck | Heat transfer for Leidenfrost drops bouncing onto a hot surface[END_REF], we developed a set-up to accurately measure the heat transfer between a single droplet and a hot wall for conditions close to LOCA.

As the interaction between the droplets and the wall is very short (~10 -4 s for the droplet size of interest) and the exchanged heat fluxes very small (a few mW), we designed an experimental test device to measure the heat transfer during the resident time and also developed a specific inverse conduction measurement technique to estimate heat flux at the wall [START_REF] Gradeck | Estimation du transfert de chaleur gouttes/paroi en situation d'APRP pour un REP[END_REF], from temperature measurements (Fig. 13).

The hot metal target (Zircaloy or Nickel -thickness representative of that of a fuel rod cladding) are heated thanks to an electromagnetic device. The inductor is a ring so that the target can be observed on both faces: on the upper face where the droplet stream impinges, a home made Planar Laser Induced Fluorescence device allows to measure the temperature of the incoming and out coming droplets while the lower face is free to be seen by an infrared camera. These two techniques and high speed camera visualizations are combined to analyse the droplet-wall interaction. As low Weber number (defined as function of droplet diameter (D), of droplet velocity (V), of fluid density (ρ) and surface tension (σ)) are expected in LOCA conditions, the main regime which has studied is the bouncing regime (see figure 14). The experiments in ambient conditions were performed with very small droplets (diameter of about 50-400µm) injected at room temperature at high frequency thanks to a purpose-designed piezoelectric nozzle where the droplet frequency, velocity (V) and size (D droplet ) at injection can be adjusted. The target wall was a very thin disk (500µm thickness) pre-heated to around 600°C by an electromagnetic inductor device. At initial time, heating was shut down and the heat flux removed from the wall by the impinging droplets (front face of the disk) was calculated by post-processing the temperature field (measured in the rear face of the disk using the infrared camera) with the aid of the semi-analytical inverse heat conduction model that was developed.

The analysis of the experimental data leads to a new model for the energy released by the wall for one droplet impact [START_REF] Gradeck | Heat transfer for Leidenfrost drops bouncing onto a hot surface[END_REF]. This model accounts for the spreading of the droplet as a function of time and for the vapour flow beneath the droplet (the model is only valid in Leidenfrost conditions). Figure 15 shows some results of the modelling compared to experimental measurements, as function of the Weber. To study LOCA conditions closely, a new set-up will be built. The test channel will be representative of a blockage zone. A given droplet distribution will be injected in the channel; this droplet distribution will be characterized using a Phase Doppler Anemometry device and both droplet distribution at the exit of the channel and global heat transfer will be measured in order to be compared with the model previously adopted [START_REF] Ruyer | Thermal hydraulic across a partially damaged core during the reflood phase of a LOCA[END_REF][START_REF] Lelong | Dynamic behaviour of droplet bouncing onto hot slab[END_REF].

CONCLUSION

The safety principle in case of a LOCA is to preserve the coolability of the core. The associated safety requirements are to ensure the resistance of the fuel rods upon quench and post-quench loads and to maintain a coolable geometry in the core. In the early 2000's, IRSN has conducted an extensive State-ofthe-Art review relative to the fuel behaviour under LOCA conditions. The PERFROI project (2014-2019) will focus on one pending question on flow blockage within a fuel rods bundle (with mechanical aspect never addressed up to now) and its potential impact on coolability (thermal hydraulics aspect) taking into account fuel relocation with electrical rods representative as much as possible to real irradiated fuel rods regarding the thermal behaviour. For this project, IRSN and partners will use existing facilities or will develop new one with innovative solutions regarding the technical measurements in order to produce enough accurate information. The results will be used to validate code modelling and the knowledge generated by the overall PERFROI project will benefit to the international nuclear safety community.

Figure 1 . 2 .

 12 Figure 1.Bundle of deformed fuel rods Figure 2. Fuel relocation in the ballooned area Phebus LOCA experiments (1983) FR2 Fuel rods fresh or irradiated (1983)

Figure 3 :

 3 Figure 3: a) ELFE facility

Figure 4 :

 4 Figure 4: measurement of the deformation

Figure 5 -

 5 Figure 5-True strain as a function of true stress: a) Tests performed between 700 and 800°C versus Frechinet results ; b)Test performed at 850°C versus Rosinger's data collection

Figure 6 -

 6 Figure 6-Phase α α α α (purple) and phase β β β β (light blue) distribution as a function of time exposure at 850°C. ELFE program will continue with isothermal creep tests on pre-oxidised and pre-hydrided zircaloy-4 followed by thermal transient tests (1-5 °C/s) on bare zircaloy-4 during 2015. Then, other cladding materials (M5 TM and Zirlo TM if available) will be studied later 2016 and 2017.

Figure . 7 :

 7 Figure .7: measurement of the deformationBefore performing the experimental program (foreseen between 2016 and 2018), it is necessary to validate the design and build a new specific test device (Fig.8) gathering high technology solutions into a millimetric space (sub channel). The main supplies, construction and qualification tests of the COCAGNE facility are foreseen to be completed early 2016.

Figure 8 scheme of COCAGNE facility Figure 9

 9 Figure 8 scheme of COCAGNE facility Figure 9 Design of the Test section

Figure 10 :

 10 Figure 10: LaMCoS-INSA Lyon facility

Figure 11 :

 11 Figure 11: Example of view given by digital image analysis

Figure. 12 :

 12 Figure.12: local phenomena involved in the process Figure. 13: Temperature measurement

Figure 14 :

 14 Figure 14: droplet-wall interaction in the bouncing regime (Weber < 40)

Figure 15 :

 15 Figure 15 : Comparison between experimental data and output of the model

2 =

 2 Temperature of the wall (°C)

  NOMENCLATURE COCAGNE : (in French language) « COmportement d'un Crayon en APRP soumis à un GradieNt de températurE » Fuel Rod Behavior under temperature gradient in LOCA conditions DRACCAR:(in French language) Déformation et Renoyage d'un Assemblage de Crayons Combustibles pendant un Accident de Refroidissement -simulation tool for 3D thermal mechanical behavior and Reflooding during LOCA transient. ELFE :(in French language) « Etablissement des Lois de FluagE » (Creep Law Determination) LOCA: Loss Of Coolant Accident

ACKNOWLEDGMENTS

This work is completed within the framework of RSNR Project from a French State aid managed by the National Agency of Research under the program of Investments for the Future carrying the reference n° ANR-11-RSNR-0017. Particular acknowledgments are also given to EDF for his financial support.


G Fernandes

Jean-Claude Gomes

Xavier Martin

Fernandes G Gomes

Interventions that provide synergistic support across all three needs tend to result in greater engagement Commercial Running Apps How Much do They Support Users' Psychological Needs?

come     Interventions that provide synergistic support across all three needs tend to result in greater engagement Commercial Running Apps How Much do They Support Users' Psychological Needs?

Introduction

Goal

Results

Discussion

Conclusion

Further research is warranted to fully understand:

•How motivational technology can encourage long-term adherence •How to develop a common framework valid for different runners' profiles

[ 1 ]

 1 Deci, E. L., & Ryan, R. M. (2008). Self-determination theory: A macrotheory of human motivation, development, and health. Canadian Psychology, 49, 182-185. [2] Fogg, B.J. (1998). Persuasive computers: perspectives and research directions. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. [3] Oinas-Kukkonen, Harri & Harjumaa, Marja. (2009). Persuasive Systems Design: Key Issues, Process Model, and System Features. Communications of the Association for Information Systems, 24.[4] Sabiston, Catherine & Vani, Madison & Jonge, Melissa & Nesbitt, Amy. (2022). Scoping reviews and rapid reviews. International Review of Sport and Exercise Psychology, 15, 1-29. [5] Orji R., and Moffatt K. (2018). Persuasive technology for health and wellness: state-of-the-art and emerging trends. Health Informatics J, 24, 66-91. [6] Fogg, B.J. (1998). Persuasive computers: perspectives and research directions. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. • Physical inactivity and sedentary lifestyles: major health-related risk factors • Promoting physical activity interventions using "motivational technology" [2] None of the apps explicitly considered any psychological needs in their design Personalization guarantees programme adherence: 1 out of 8 apps had tailored motivational messages SDT dimensions included in the selected running apps Autonomy: All apps to some extent Competence: 6 out of 8 Relatedness: All apps but in different forms All of the 5 other apps mainly satisfied feeling of being autonomous and always having the choice of one's actions Competence: relates to the feeling that one can be effective and capable Affiliation: linked to the need for social ties; to feel close and valued by others How running apps support the three basic psychological needs? of the top ranked commercial running apps for 2022 Inclusion criteria: most popular and used apps with a clear running goal Total of 8 running apps Plus 5 other applications and web services with particular features SDT -Basic Psychological Needs Self-Determination Theory; SDT [1] : Interventions to improve maintenance of physical activity behavior exist Lack of interventions that fit different populations and needs in the mid-long term Research suggests the importance of tailored interventions