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We introduce here a two-component annulationstrategy that provides access to a diverse collection of five- and six- membered saturated heterocycles from aryl alkenes and a family ofredox-active radical precursors bearing tethered nucleophiles. This transformation is mediated by a combination of an Ir(III)photocatalyst and a Brønsted acid under visible-light irradiation. A reductive proton-coupled electron transfer generates a reactiveradical which undergoes addition to an alkene. Then, an oxidative radical-polar crossover step leading to carbocation formation isfollowed by ring closure through cyclization of the tethered nucleophile. A wide range of heterocycles are easily accessible,including pyrrolidines, piperidines, tetrahydrofurans, morpholines, δ-valerolactones, and dioxanones. We demonstrate the scope of this approach through broad structural variation of both reaction components. This method is amenable to gram-scale preparation and to complex fragment coupling.

La prévalence des allergies alimentaire (AA) est en augmentation depuis quelques années. Elles sont la première cause de réaction anaphylactique chez les enfants et adolescents. La prévention de ces réactions allergiques alimentaires se fait via une éviction totale des aliments allergènes. Cependant, les conséquences de cette alimentation restrictive à long terme, particulièrement dans le cadre familial et social, sont peu développées dans la littérature. Cette revue systématique avait pour but de rechercher, d'analyser et de synthétiser les conséquences liées à un régime d'éviction dans le cadre d'allergies alimentaires chez les enfants de 2 à 18 ans.

Photoredox catalysis has provided many approaches to C(sp3)–H functionalization that enable selective oxidation and C(sp3)–C bond formation via the intermediacy of a carbon-centered radical. While highly enabling, functionalization of the carbon-centered radical is largely mediated by electrophilic reagents. Notably, nucleophilic reagents represent an abundant and practical reagent class, motivating the interest in developing a general C(sp3)–H functionalization strategy with nucleophiles. Here we describe a strategy that transforms C(sp3)–H bonds into carbocations via sequential hydrogen atom transfer (HAT) and oxidative radical-polar crossover. The resulting carbocation is functionalized by a variety of nucleophiles—including halides, water, alcohols, thiols, an electron-rich arene, and an azide—to effect diverse bond formations. Mechanistic studies indicate that HAT is mediated by methyl radical—a previously unexplored HAT agent with differing polarity to many of those used in photoredox catalysis—enabling new site-selectivity for late-stage C(sp3)–H functionalization., When carbon-based units are functionalized in photoredox catalysis, electrophilic coupling partners are often used, such that the polarities of the two fragments are appropriately matched. Here the authors show a generalized methodology to instead use nucleophilic coupling partners, which are cheaper and often simpler, via successive hydrogen atom transfer and oxidative radical-polar crossover.

This article deals with the assessment of severe accident event sequence and mitigation strategy elaboration performed in the frame of ASTRID SFR Gen IV reactor project (Le Coz et al., 2013), including the Japanese/French collaboration involving JAEA, MFBR, Framatome and CEA. In the first part of the paper, the mitigation strategy and the approach defined for the design of mitigation features, which are transverse tubes called DCS-M-TT are presented. By considering 21 DCS-M-TTs into the core as defined at the end of the conceptual design, which enable to extract the core materials and to significantly reduce the core reactivity within the order of 10 s in some typical accidental conditions, the accidental power excursions in ASTRID should not lead to a significant mechanical energy release, thus ensuring the integrity of the main vessel. Nevertheless, some loading assumptions independent from event evolutions have been defined in order to design the main vessel and the core catcher in order to cover extreme accident consequences and to get rid of event sequence dependency when designing the reactor. Then, SIMMER-IV (3D) the main calculation results of ULOF simulations whose goal was to verify the DCS-M-TT efficiency and to support a PIRT are highlighted in the paper. They confirmed that fuel discharge through discharge tubes has a large mitigating impact on power excursions. The last part of this paper deals with an approach dedicated to the description of severe accident event sequences through generic event trees (GETs), which logically summarize the representative courses of accident progression showing relationship between critical causal events and major outcomes of the accidents. A set of trees has been elaborated for the description of each event sequence able to cause severe accidents (ULOF: unprotected loss of flow, UTOP: unprotected transient overpower and USAF: unprotected sub-assembly fault). The event-tree bifurcation points towards one branch or another of the possible event evolution could be examined alternatively with a help of phenomenological event chart (PECs). Afterwards, in association with the GET analysis, a PIRT (Phenomenon identification ranking table) on ULOF has been developed conjointly by Japanese and French sides in order to prioritize RD the primary phase, the short-term relocation phase, the expansion phase and the long-term relocation and cooling phase.

International audience; Within the framework of the French 4th-generation Sodium-cooled Fast Reactor safety assessment, methodology on VVUQ (Verification, Validation, Uncertainty Quantification) is conducted to demonstrate that the CEA's thermal-hydraulic Scientific Computation Tools (SCTs) are effective and operational for design and safety studies purposes on this type of reactor. This VVUQ-based qualification is a regulatory requirement from the French Nuclear Safety Authority (NSA). In this paper, the current practice of VVUQ approach application for a SFR accidental transient is described with regard to the NSA requirements. It constitutes the first practical, progressively improvable approach. As the SCT is qualified for a given version on a given scenario, the transient related to a total unprotected station blackout has been selected. As it is a very complex multi-scale transient, the SCT MATHYS (which is a coupling of the CATHARE2 tool at system scale, TrioMC tool at component scale and TrioCFD tool at local scale) is used. This paper presents the preliminary VVUQ application to the qualification of this tool on this selected transient. In addition, this work underlines some feedback on design and R&D aspects that should be addressed in the future to improve the SCT.

International audience; A cross-comparison of four Generation IV reactor concepts and a PWR of 2nd generation is presented in this paper. 4 Gen IV reactor concepts are considered and are briefly presented in the first part of the paper: SFR of 1500 MWth, GFR of 2400 MWth, MSR of 3000 MWth and VHTR of 600 MWth. In order to perform this comparison, some simple common criteria related to accidental behavior of the reactors have been developed. The first kind of criteria aims at assessing the main physical thresholds to exceed in order to have a core degradation: phase changes of coolant and of core materials (including the effect of chemical reactions) for the various reactor concepts considered. The second set of criteria deals with kinetics aspects of the accident. On the basis of core power (after scram and without scram), on the coolant inventory and on the reactor capability to be passively cooled, the heating rate of the coolant and of the core materials are assessed thanks to simplified energy balances presented in the paper. As a result, for each reactor concept, the time to reach the physical thresholds defined above is evaluated. A third set of criteria deals with core features and aims at assessing the possible reactivity insertion that withstands each concept up to core melting (or boiling for the MSR) and the associated expected power peaks in case of coolant voiding/depressurization and in case of fissile material compaction. Finally, a last criterion set deals with the assessment of the possibility to jeopardize physical barriers confining fission products. These criteria deal with the risk of barrier loadings due to coolant and core material vaporization depending on the features of the coolant/fuel and on the operating point of each reactor concept. In the last part of the paper, a synthesis is made in order to underline the weak and strong points of each of the reactor concepts investigated in terms of severe accident prevention and mitigation

The nuclear safety approach has to cover accident sequences involving core degradation in order to develop reliable mitigation strategies for both existing and future reactors. In particular, the long-term stabilization of the degraded core materials and their coolability has to be ensured after a severe accident. This paper focuses on severe accident phenomena in pressurized water reactors (PWR) compared to those potentially occurring in future GenIV-type sodium fast reactors (SFR). First, the two considered reactor concepts are introduced by focusing on safety aspects. The severe accident scenarios leading to core melting are presented and the initiating events are highlighted. This paper focuses on in-vessel severe accident phenomena, including the chronology of core damage, major changes in the core configuration and molten core progression. Regarding the mitigation means, the in-vessel retention phenomena and the core catcher characteristics are reviewed for these different nuclear generation concepts (II, III, and IV). A comparison between the PWR and SFR severe accident evolution is provided as well as the relation between governing physical parameters and the adopted mitigation provisions for each reactor concept. Finally, it is highlighted how the robustness of the safety demonstration is established by means of a combined probabilistic and deterministic approach.

Objectives To estimate the prevalence of understated cognitive impairment by administering the Clock-Drawing Test (CDT) to community-dwelling individuals aged ≥50 years and to investigate the associated clinical phenotype. Design A cross-sectional analysis of baseline data on community-dwelling individuals assessed at an outpatient clinic in the Paris region of France. Setting and Participants Participants aged ≥50 years (n = 488, median age: 62.1 years) prospectively included in the SUCCessful agEing outpatiEnt's Department survey between 2010 and 2014. Methods A multidimensional geriatric assessment, including cognition [7-point CDT, Mini-Mental State Examination (MMSE), the 5-word screening test (5-WT), and the Frontal Assessment Battery (FAB)], gait speed in dual tasks, mood [the Geriatric Depression Scale (GDS)], balance, physical functions (gait speed and handgrip strength), nutrition, bone density, and comorbidities; major cardiovascular risk factors, and Scheltens and Fazekas scores on brain magnetic resonance imaging. Baseline characteristics were analyzed as a function of the CDT score ( Results The prevalence of impairment in the CDT was 23.6%; higher than the values for the MMSE (12.7%), 5-WT (2.3%), and FAB (16.6%). In age-adjusted analyses, a lower educational level (odds ratio [95% confidence interval] = 0.72 [0.58‒0.89]), diabetes (2.57 [1.14‒5.79]), metabolic syndrome (1.93 [1.05‒3.56]), lower gait speed in the cognitive dual task (1.27 [1.05‒1.53]), a poorer Geriatric Depression Scale score (1.86 [1.04‒3.32]), a poorer MMSE score (2.56 [1.35‒4.88]), a poorer FAB score (1.79 [1.01‒3.16]), impaired episodic memory in the 5-WT (4.11 [1.12‒15.02]), and a higher Scheltens score (P = .001) were significantly associated with CDT impairment. Conclusions and Implications Understated cognitive impairment is common among young seniors and is associated with factors known to be linked to a higher risk of cognitive decline and dementia. These findings suggest that the CDT may be of value for identifying high-risk individuals who may then benefit from targeted multidomain prevention actions (diet, exercise, cognitive training, and vascular risk factor management).

A unique collaboration between academic scholars, legal practitioners, and arbitrators, this handbook focuses on the intersection of arbitration - as an alternative to litigation - and the court systems to which arbitration is ultimately beholden. The first three parts analyze issues relating to the interpretation of the scope of arbitration agreements, arbitrator bias and conflicts of interest, arbitrator misconduct during the proceedings, enforceability of arbitral awards, and the grounds for vacating awards. The next section features fifteen country-specific reviews, which demonstrate that, despite the commonality of principles at the international level, there is a significant amount of differences in the application of those principles at the national level. This work should be read by anyone interested in the general rules and principles of the enforceability of foreign arbitral awards and the grounds for courts to vacate or annul such awards.

ISBN 978-1-5272-6447-2; International audience; Three sub-critical (SC) core configurations were investigated in the VENUS-F zero power reactor coupled with the GENEPI-3C accelerator. The SC10 and SC12 were a mock-up of a MYRRHA start-up core and SC11 represented a more complex MYRRHA core loaded with various types of in-pile-sections. The sub-criticality of 11 variants of these VENUS-F cores was changed in several steps from -6$ down to -30$ using the safety and control rods. Their sub-criticalities were determined with the Source Jerk Integral (SJI) method using 11 fission chambers located all over the reactor. For the data analysis, the 8-group delayed neutron parameters from the JEFF-3.1.2 evaluated nuclear data library were used. Reliability and reproducibility of the experimental results were tested by repeating the measurements, swapping the detectors and varying the accelerator beam intensity, thus changing the detector count rates and verifying the validity of the dead time corrections. The obtained results are compared with MCNP calculations.

Within the framework of the Generation IV Sodium-cooled Fast Reactor (SFR) RD its final objective being to derive the variability of the main outputs of interest for the safety. This approach involves a fast-running description of extended accident sequences coupling physical models for the main phenomena with advanced statistical analysis techniques. It enables to perform a large number of simulations in a reasonable computational time and to describe all the possible bifurcations of the accident transient. In this context, this paper presents a physical tool (models and results assessment) dedicated to the primary phase of an Unprotected Loss Of Flow accident (ULOF) in a SFR, i.e. before the first hexagonal can failure. This paper focuses on the modeling of neutronic phenomena and of the pin degradation and on their validations, the two-phase sodium thermal–hydraulic behavior having largely been assessed in a previous paper. The physical tool called MACARENa is described before presenting the comparison of its results with experimental tests results for the pin degradation behavior modelling and with mechanistic SIMMER-III code results for the global core behavior evolution during an ULOF transient. This tool is demonstrated to be capable of reproducing the mass-flow rate, reactivity, power evolution, and global pin degradation behaviour during an ULOF with a low discrepancy regarding the same transient simulated with SIMMER-III. In particular, observed discrepancies concerning mass flow rates and power evolutions are under 3 % before boiling occurs and, later during the transient, the power excursion starts only 2 s earlier in the MACARENa simulation than in the SIMMER-III one. The fast-running tool has then been used for safety-informed design and flow stability analyses of fast reactor systems, more specifically dealing with the ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) core concept. It allowed to emphasize the main dominant phenomena and the significant trends for safety assessment. This work has pointed out the strong impact of the modelling of reactivity feedback due to thermal expansion on the resulting core degradation during an ULOF. It has also highlighted the main scenario parameters and models influencing this transient evolution.

Acute physical exercise improves memory functions by increasing neural plasticity in the hippocampus. In animals, a single session of physical exercise has been shown to boost anandamide (AEA), an endocannabinoid known to promote hippocampal plasticity. Hippocampal neuronal networks encode episodic memory representations, including the temporal organization of elements, and can thus benefit motor sequence learning. While previous work established that acute physical exercise has positive effects on declarative memory linked to hippocampal plasticity mechanisms, its influence on memory for motor sequences, and especially on neural mechanisms underlying possible effects, has been less investigated.Here we studied the impact of acute physical exercise on motor sequence learning, and its underlying neurophysiological mechanisms in humans, using a cross-over randomized within-subjects design. We measured behavior, fMRI activity, and circulating AEA levels in fifteen healthy participants while they performed a serial reaction time task (SRTT) before and after a short period of exercise (moderate or high intensity) or rest.We show that exercise enhanced motor sequence memory, significantly for high intensity exercise and tending towards significance for moderate intensity exercise. This enhancement correlated with AEA increase, and dovetailed with local increases in caudate nucleus and hippocampus activity.These findings demonstrate that acute physical exercise promotes sequence learning, thus attesting the overarching benefit of exercise to hippocampus-related memory functions.

Es werden immer neue Technologien entwickelt oder weiterentwickelt, da die Erwartungen an Computer immer weiter steigen und mehr und mehr Menschen sich mit dem Computer verständigen können möchten. Artificial Intelligence ist eine dieser Technologien, die seit den 1950er Jahren einen großen Aufschwung erlebt, ständig weiterentwickelt wird und in immer mehr Produkte eingebaut wird. Forschungen schaffen immer intelligentere Maschinen, um die ständig steigende Nachfrage nach neuen Technologien decken zu können. Das Ziel bei der Entwicklung einer Künstlichen Intelligenz ist es, dass der Computer eigenständig kombinieren und interagieren kann. Dies wird bewerkstelligt indem dem Computer ein ausreichend großer Trainingsdatensatz zur Verfügung gestellt wird, mit welchem dem Computer zum Beispiel beigebracht wird ob ein Tier auf einem Foto eine Katze oder ein Hund ist. Im Gegensatz zum herkömmlichen Programmieren, wird dem Computer nicht explizit vorgegeben, ein Bild als Katze zu kategorisieren, wenn diese Eigenschaften auftreten, sondern der Computer findet die Merkmale eigenständig und bekommt lediglich die Information das dieses Foto im Trainingsdatensatz eine Katze ist und dieses ein Hund. Da intelligente Maschinen immer stärker in den Alltag integriert werden, beschäftigt sich diese Bachelorarbeit mit den Begriffen Artificial Intelligence, Machine Learning und Deep Learning durch eine Literatur- und Internetrecherche und arbeitet hierbei vor allem die Unterschiede heraus, da diese Begriffe häufig verwechselt werden. Außerdem werden diese Begriffe detaillierter erklärt. Die Hauptbereiche von Artificial Intelligence werden aufgeschlüsselt und anhand von Beispielen verdeutlicht. Der Fokus liegt auf Artificial Intelligence da Machine Learning und Deep Learning in der Regel als Teilbereiche von Artificial Intelligence verstanden werden. Außerdem werden in dieser Bachelorarbeit einige praktische und auch bekannte Beispiele von Artificial Intelligence angeführt und detailreicher beschrieben. As the expectations for computer abilities still grow and more and more people want to be able to communicate with computers, new technologies are being developed and improved. Artificial Intelligence is one of such technologies, that has experienced a big boom since the 1950s and is being improved and integrated into even more products since then. Research has created more and more intelligent machines to be able to keep up with the constantly rising demand of new technologies. The goal of developing Artificial Intelligence is to create a computer that can make decisions and interact with people on its own. This is achieved by giving the computer a training data set that is big enough for the computer to be able to learn. In contrast to conventional programming, the computer is not told that a picture has to be a certain topic if certain criteria are being fulfilled, but instead only the information is given that a certain picture in the data set is the picture of a certain topic and the computer has to figure out which criteria makes a picture an image of this topic. As intelligent machines are getting more and more important in daily life, this bachelor thesis deals with definitions of Artificial Intelligence, Machine Learning and Deep Learning through literature and internet research and in particular works out the differences between these terms, as they are often being confused. Furthermore, these terms are being explained in more detail and the main fields of Artificial Intelligence are broken down and illustrated through concrete examples. The focus of this thesis is on Artificial Intelligence, as Machine Learning and Deep Learning are often considered as subfields of Artificial Intelligence. In this thesis some practical and well-known examples of Artificial Intelligence will also be discussed.

Functional data consist in the most typical case of one-dimensional curves that represent the evolution of some physical parameter of interest with time. However, the analysis of this kind of objects is far from being simple, and the possibility of treating contaminated data is a classical problem that can arise in this framework as frequently as in the multivariate one. This justifies the development a new functional outlier detection technique based on functional measures capable of capturing the the outlyingness in the magnitude and shape sense that is presented in this paper.

International audience; Usually, simulation tools are validated on experimental data considering a Best Estimate simulation case and there is no quantification of this validation, which remains based on a rough expert judgment. This paper presents an advanced validation treatment of the simulation tool OCARINa, devoted to Unprotected Transient OverPower (UTOP) accidents, on two CABRI tests, considering this time, a Best Estimate Plus Uncertainties (BEPU) approach. The output results of interest are both scalar physical data such as the time and location of the pin failure and associated molten mass and vector data such as temperature axial distribution or temperature evolution versus time. This approach is a first step in quantifying the degree of agreement between the calculation results and the experimental results. It is of great interest for the VV&UQ (Verification, Validation and Uncertainty Quantification) approach, which leads to the qualification of scientific calculation tools.

A coupled thermalhydraulic-neutronic extended criterion developed in order to assess the conditions of static instability of the sodium flow in a SFR core during the beginning of an unprotected loss of flow (ULOF) is presented in the first part of this paper. This extended criterion takes into account the evolution of the pressure drop in a sub-assembly (SA) as well as the evolution of its power when the reactor is affected by a flow rate (or power) perturbation by starting from a steady-state. The considered steady states are typical of quasi-steady states reached by a SFR during a ULOF. The temporal evolution of the flow and the temporal evolution of the power can be represented by a system of two differential equations whose linear stability analysis has enabled to define the aforementioned extended criterion. Then, in the second part of the paper, a verification of this extended criterion is performed by simulating the behavior of a GEN IV SFR of 1500 MWth. Four various steady states of the reactor have been investigated with a simulation tool devoted to unprotected loss of flow simulations (MACARENa). First simulations have enabled to calculate the various physical parameters needed to check the extended criterion. Perturbations have been applied to these four states. The extended criterion, proposed in this paper, has predicted flow stabilization for 3 states whereas it has predicted a flow excursion (sudden flow rate decrease leading to SA dry-out) for the last state. In this latter case, the classical Ledinegg criterion, which relies only on pressure drop evolution at constant power, has predicted a stable configuration. Then, the extended criterion predictions have been verified with MACARENa simulations, by slightly and temporary reducing the driving pressure head of the flow rate in the studied SA from each of the four initial states. For stable states, when setting again the pressure head of the flow to the value of the initial state, the initial flow rate is recovered. For the last initial state (predicted as unstable by the extended criterion), after a convergence period carried-out by imposing the SA steady flow rate, the solving of the transient momentum equation have shown that a flow excursion occurs in the MACARENa simulation as expected from the extended criterion. Consequently, the extended criterion proposed in this paper has been verified and could enable to define stable and unstable domain of couple flow rate/power in order to design future cores.

This paper presents a statistical methodology for a quantified validation of the OCARINa simulation tool, which models the unprotected transient overpower (UTOP) accidents. This validation on CABRI experiments is based on a best-estimate plus uncertainties (BEPU) approach. To achieve this, a general methodology based on recent statistical techniques is developed. In particular, a method for the quantification of multivariate data is applied for the visualization of simulator outputs and their comparison with experiments. Still for validation purposes, a probabilistic indicator is proposed to quantify the degree of agreement between the simulator OCARINa and the experiments, taking into account both experimental uncertainties and those on OCARINa inputs. Going beyond a qualitative validation, this work is of great interest for the verification, validation and uncertainty quantification or evaluation model development and assessment process approaches, which leads to the qualification of scientific calculation tools. Finally, for an in-depth analysis of the influence of uncertain parameters, a sensitivity analysis based on recent dependence measures is also performed. The usefulness of the statistical methodology is demonstrated on CABRI-E7 and CABRI-E12 tests. For each case, the BEPU propagation study is carried out performing 1000 Monte Carlo simulations with the OCARINa tool, with nine uncertain input parameters. The validation indicators provide a quantitative conclusion on the validation of the OCARINa tool on both transients and highlight future efforts to strengthen the demonstration of validation of safety tools. The sensitivity analysis improves the understanding of the OCARINa tool and the underlying UTOP scenario.

Raymond Federman (1928-2009) was known as a Beckett scholar, postmodern theorist and avant-garde fiction writer. Born in Paris, Federman escaped deportation during the Nazi occupation. All members of his immediate family perished at Auschwitz. He immigrated to the United States and in 1965 published one of the first monographs on Samuel Beckett, Journey to Chaos: Samuel Beckett’s Early Fiction. He kept writing on Beckett but turned his focus to postmodern theory, coining the terms ‘critifiction’ and ‘surfiction’ to describe his work and that of his contemporaries. Federman’s novels all repeat variations of his own life story. Scholarship on Federman has acknowledged Beckett’s importance, but the depth of this relationship is yet to be explored. This thesis offers a close reading of both the apparent and encoded intertextuality with Beckett in Federman’s writing. In telling his story Federman merges it with the stories of Beckett’s creations, grafting parts of their identity onto his own. These dynamics are especially significant in the early cycle of Federman’s oeuvre, from the 1971 Double or Nothing to the 1982 The Twofold Vibration.Federman was also, like Beckett, a self-translator. By engaging with Beckett bilingually, he critiques and reveals both his own writing process and his complex relationship to the man he called ‘Sam.’ Behind or beyond Beckett lies James Joyce, his creation and alter ego ‘Shem the Penman.’ Federman arrives at Joyce through Beckett, disrupting the order of literary transmission, to claim the Pen Man as his own. He engages with Beckett and Joyce as novelist and critic simultaneously, leading us to reflect on the complexities of personal identification and scholarly tribute.

Delayed-neutron (DN) data is essential in inherent reactor safety and reactor control since it is needed for the estimation of the reactivity. Nowadays, discrepancies among the data in various international databases (JEFF, ENDF, JENDL) are large and bring excessive conservatism in the safety margins. The ALDEN (Average Lifetime of DElayed Neutrons) experiment, built in a collaboration between CEA and CNRS, aimed at re-measuring the DN data associated with several fissioning systems (average delayed-neutron yield and kinetic parameters). The first experimental campaign consisted in the integral measurement of the DN activity after the irradiation of an 235U target. It took place under the cold neutron flux of ILL (Institut Laue-Langevin) at the beginning of September 2018, in the PF1b experimental zone (doi:10.1016/j.nima.2006.03.020). The data analysis gave an average DN yield of 1.631E-02(2) DN/fiss and a mean precursors’ half-life of 8.93(9) s. The results are consistent with the literature, but they are affected by one third of the uncertainty.

International audience; In this article, we evaluate the quality and robustness of a method envisaged for the on-line monitoring of the subcriticality of an ADS, called the ‘‘current-to flux” (CTF) method. For this evaluation, we performed a dedicated experiment at the GUINEVERE facility. It is hosted at the SCK-CEN and consists of the subcritical VENUS-F reactor coupled to a continuous external neutron source provided by the GENEPI-3C accelerator. During this experiment, the reactor control rods were moved in various patterns, and the subsequent dynamical evolutions of the reactor reactivity were monitored using nine fission chambers (FCs). The space-energy effects that bias the reactivity values are corrected using a procedure based on simulations computed with the Monte Carlo neutron transport code MCNP. We investigate the precision of this correction procedure by comparison with a reactivity value extracted with the beam interruption technique and we demonstrate its insensitivity to the simplifications made on the VENUS-F reactor modeling and to a simulation key parameter such as the boron carbide density filling the control rods.

International audience; Sodium-cooled Fast Reactors (SFR) are investigated as future Generation IV reactor concepts. In SFR, the core configuration is not the most reactive during the nominal reactor operation, its geometry change or coolant voiding can induce a reactivity insertion. Within these considerations, mitigation devices should be implemented into the core in order to limit the thermal energy released into the fuel during a severe accident and thereby the possibility to induce mechanical loadings of the reactor structure when vaporized materials expand. Complementary safety devices called Transfer Tubes (TT) are studied in a French concept as an effective mitigation measure of severe accidents to reach a final reactor safe state, even in case of a failure of all shutdown systems including the passive shutdown safety rods. More precisely the TT, with their upper part located in and above the core, cross the core support structure and are linked to the core catcher zone situated in the main vessel bottom. Their purpose is to extract fissile materials from the core zone and secondly to favour the transfer of the molten fuel from the core region to the core catcher in case of severe core damage. The fuel discharge out of the core zone is necessary in order to lower the core reactivity, the relocation into the core catcher is necessary to enable the stabilization, the sub-criticality and the fuel cooling. An extensive work on severe accident calculations and phenomena identification related to fuel discharge through TT was performed. These studies represent the outcome of the work performed in 2014-2019, performed with collaboration of Japanese JAEA and MFBR and Framatome in the framework of the SFR project carried out by CEA. Calculations of fuel discharge were carried out with the mechanistic calculation code SIMMER and the main results are presented in this paper. Firstly, the whole unprotected loss of flow (ULOF) accident sequence was calculated with the SIMMER code. From these calculations, the power and flow evolution were set as boundary conditions for a more detailed model with six fuel assemblies around TT. This model was used to focus on key phenomena and to check impact of design parameter as local bottom restriction inside TT on fuel discharge way.

The present paper is dedicated to the studies carried out during the first stage of the pre-conceptual design of the French demonstrator of fourth generation SFR reactors (ASTRID) in order to compare the behaviour of two envisaged core concepts under severe accident transients. Among the two studied core concepts, whose powers are 1500 MWth, the first one is a classical homogeneous core (called SFRv2) with large pin diameter whose the sodium overall voiding reactivity effect is 5 $. The second concept is an axially heterogeneous core (called CFV) whose global void reactivity effect is negative (−1.2 $ at the end of cycle at the equilibrium). The comparison of the cores relies on two typical accident families: a reactivity insertion (unprotected transient overpower, UTOP) and an overall loss of core cooling (unprotected loss of flow, ULOF). In the first part of the comparison, the primary phase of an UTOP is studied in order to assess typical features of the transient behaviour: power and reactivity evolutions, material heating and melting/vaporization and mechanical energy release due to fuel vapor expansion. The second part of the comparison deals with the calculation of the reactivity potential for degraded states (molten pools) representative of the secondary phase of a mild UTOP and of a strong UTOP (strong or mild qualifies the reactivity ramp inserted). According to the reactivity potential, the amount of fuel to extract from the core and the amount of absorber material to inject in the pool of molten fuel in order to compensate this potential are calculated. These amounts give an order of magnitude of the strength of the mitigation actions required for each type of core in order to limit the mechanical energy release due to secondary power excursions. The calculation results have shown that in case of UTOPs (ramp ranging from several $/s to 60 $/s), the mechanical energy released by the expansion of a fuel vapor bubble is about one order of magnitude lower for the CFV core than for the SFRv2 core. Moreover, in case of core melting due to an UTOP, both cores require approximately the same amount of absorber material to be inserted in order to reach a sub-critical state. For the same degraded state a zero reactivity could be reached with a lower amount of fuel extracted from the CFV core than from the SFRv2 core. Regarding ULOFs, the assessment of the reactivity that could be induced by molten cladding relocation has shown a largely better behaviour for the CFV core. More precisely, for this latter core design, a severe power excursion induced by cladding relocation is very unlikely. Finally, the times of boiling onset, of flow redistribution in the core and of material melting, indicate that mitigation actions (absorber insertion and fuel extraction) should start earlier for the SFRv2 core than for the CFV one. This result is a good point for the CFV core because it allows later mitigation actions which are more likely to succeed because time is required to initiate the fuel relocation through in-core dedicated ducts. The results presented in this paper have contributed to retain the CFV core for the studies currently carried-out for the ASTRID design.