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International audience; On October 1, 2018, 452 nuclear water reactors were operating in the world mainly of second generation (PWR or BWR). The first third generation reactors, EPR and AP1000, have just started in China, and 2 two other ones should start next year in Europe. All these reactors produce spent fuel. Some countries have decided to manage this spent fuel as a final waste. In France, a reprocessing of this fuel is carried out in order to separate the uranium and the plutonium remaining in this spent fuel (96% of the total mass of the spent fuel) and reused as MOX fuel. Only 4% of the spent fuel is sent in to the final waste. Reprocessed uranium is stored as a strategic resource whereas plutonium is reused once in MOX fuel. Today, only a mono-recycling of the Pu plutonium is implemented, because of the difficulties to use it a second time in the REPPWR, mainly due to its isotopic composition. Only a reactor with a fast neutron spectrum, for example a Sodium Fast Reactor (SFR), makes the multi-recycling of the plutonium efficient by taking advantage of a higher ratio of fission vs over capture. This strategy was validated by reprocessing MOX assemblies from the French Phenix SFR, and by remanufacturing fresh fuel from the recycled Pu that was irradiated again in Phenix. This experiment demonstrates the feasibility of this actinides recycling by fast reactors. Molten Salt Reactors (MSR) with a fast neutron spectrum would also be potentially able to burn this waste while producing energy. The final performance obtained by burning plutonium or final waste is fairly comparable for any fast reactor. But on the other hand, the MSRs would allow this operation to be achieved in one step, through a continuous multi-recycling and without cumbersome operations to make new fuel assemblies, which entails considerable time and money savings. A concept of fast MSR of 3000 MWt, the MSFR (Molten Salt Fast Reactor) has been studied in France since 15 years by the CNRS and then further developed within European projects. The main technical choices for this reactor, used for this simulation, are explained. Several options are given on the way to use the MSFR as a burner of final products today available after reprocessing. In the first case, the reactor is used as burner of available depleted uranium and plutonium oxide recovered from the reprocessing. These products are fluorinated and introduced into the reactor to achieve criticality. The evolution of the composition of the salt during the operation is given as well as the periodic additions made, and the corresponding consumption by TWh produced. The evolution of the composition of other specific elements that could alter the physico-chemical properties of the salt or the neutronic performances of the reactor (such as the lanthanides) are also given since a specific treatment of the salt has to be developed to extract them. The same exercise is repeated in a second case with the assumption that a reprocessing of a spent MOX has been made that gives a new composition of the plutonium. In Finally in a third option, all the minor actinides (americium, curium and neptunium) are recovered and recycled together, with uranium and plutonium. The possible consumption of waste by TWh produced is determined. Changes in the composition of salt over time give also an idea of the quantities of products to be extracted by salt treatment. In conclusion, this paper gives quantitative estimations of the possibilities to operate a MSR in the U/Pu fuel cycle using only the available products obtained by reprocessing the spent nuclear fuel of a fleet of second-or third-generation water reactors.

International audience

International audience; The CNRS has focused R&D e˙orts on the development of a new reactor concept called the Molten Salt Fast Reactor (MSFR). The MSFR, characterized by a circulating liquid fuel and a fast neutron spectrum, has been identified as a very interesting long term alternative to solid fuelled fast neutron systems in the Gen4 International Forum.MSRs are liquid-fuelled reactors so that they are flexible in terms of operation or design choices, but they are very di˙erent in terms of design and safety approach compared to solid-fuelled reactors. The MSFR system includes three di˙erent circuits: the fuel circuit, the intermediate circuit and the power conversion circuit, together with normal and emergency draining tanks and on-site fuel processing units. This paper will focus on the new designs developed for the fuel circuit and the emergency draining system of the MSFR in the frame of the SAMOFAR European project. The fuel circuit, defined as the circuit containing the fuel salt during power generation, includes the core cavity and the recirculation/cooling sectors. These new designs result from physical and preliminary safety studies such as for the fuel circuit optimizing the use of the molten salt both as fuel and coolant, defining the operating procedures and minimizing the fuel leakage risks. Additional requirements are considered for the emergency draining system to be able to confine the fuel and to evacuate the residual heat over very long time periods (months) with no human intervention and to guaranty that under no circumstance the salt may reach criticality in this area.

ISBN 978-4-89047-167-6; International audience; Molten salt reactors are liquid-fueled reactors so thatthey are flexible in terms of operation (load-followingcapabilities…) or design (core geometry, fuel composition,specific power level…) choices, but they are very differentin terms of design and safety approach compared to solidfueledreactors. Such reactors call for a new definition oftheir operating procedures. Dedicated studies areperformed in the frame of the European SAMOFAR (SafetyAssessment of Molten Salt Fast Reactors) project ofHorizon2020. This paper focuses on the behavior of theMSFR fuel circuit in interaction with the intermediatecircuit. It is devoted to the start-up procedure of the MSFR,including the description of the proposed procedure, apresentation of the approach to criticality and thereactivity measurement during the filling of the core, andfinally studies of accident scenarios (overcooling,reactivity insertion) at low power during the divergencestep of the MSFR, highlighting the very good behavior ofthe reactor to such abnormal transients.

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ISBN 978-92-950641410; International audience

Proc. on CD Rom paper 11190; International audience

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paper 9207; International audience; Essentially, because the salt is the moderator, the coolant and the fuel, the study of Molten Salt Reactor are specific. There are strong coupling between neutronics, and other part of physic field like the chemistry for instance. The system presented in this paper is called Molten Salt Fast Reactor which is a molten salt reactor with no moderator inside the core with a salt composition which leads to a fast neutron spectrum. Previous studies showed that this concept (previously called Thorium Molten Salt Reactor – Non moderated) has very promising characteristics. We tried to explain computational problems due to the study of this concept, especially the coupling with the reprocessing and with the chemistry. Indeed, the reprocessing is done little by little in situ, so we have to consider it in our studies. We also show that the redox properties changes during operation because fissions change the salt chemistry (it is a reductive process). Our program is a coupling between MCNP and a home made evolution code called REM. It was validated for thermal neutron and epithermal neutron spectrum but not for fast neutron spectrum, so a brief study with ERANOS of the MSFR is also presented here.

paper 9149; International audience; Molten salt reactors in the present configuration, called Molten Salt Fast Reactors (MSFR), have been selected for further studies by the Generation IV International Forum. These reactors, characterized by a fast neutron spectrum, may be operated in simplified and safe conditions in the Th/233U fuel cycle with fluoride salts. Since 233U does not exist on earth and is not being directly produced today, we investigated the possibility of using, in this MSFR concept, the transuranic elements (TRU) currently produced in the world as an initial fissile load. We present here the concept, before focusing on a possible optimization in terms of minimization of the initial fissile inventory and improvement of the burning efficiency. Our studies demonstrate that an initial fissile inventory around 4 to 5 metric tons per GWe may be easily reached with a burning rate after 50 years of operation ranging from 87% to 93%. These studies also bring to light the limitations of the concept due to the irradiation damages to the structural materials. We conclude that this issue will have to be studied in depth to allow a realistic evaluation of the global possibilities of such a reactor.

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The PHYSOR'08 Proceedings, providing all the 447 full papers presented, are available as a CD-ROM; International audience

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Colloque avec actes et comité de lecture. Internationale.; International audience; Nous présentons des expériences, utilisant la technique du creuset froid, dans lesquelles des lanthanides, ou d'autres éléments, sont transférés d'une phase saline fluorée vers une phase métallique liquide contenant un agent réducteur tel le Lithium. Du ZrF4 (5 mol%), ou bien du CeF3 (2 mol%), est dissous dans du LiF. Un alliage métallique Sb-Li contenant 5 ou 10 wt % de Lithium, est mis en contact de la phase saline à t = 0. Le taux de transfert est déduit des analyses ICP post mortem effectuées sur des échantillons prélevés dans le métal à pas de temps donnés. La cinétique du transfert est très rapide et dépend de l'agitation électromagnétique.

Molten salt reactors, in the configuration presented here and called Thorium Molten Salt Reactor (TMSR), are particularly well suited to fulfil the criteria chosen by the Generation IV forum, and may be operated in simplified and safe conditions in the Th/233U fuel cycle with fluoride salts. Amongst all MSR configurations in the thorium cycle, many studies have highlighted the configurations with no moderator in the core as simple and very promising. Since 233U does not exist on earth and is not being produced today, we aim at designing a critical MSR able to burn the Plutonium and the Minor Actinides produced in the current operating reactors, and consequently to convert this Plutonium into 233U. This leads to closing the current fuel cycle thanks to TMSRs started with transuranic elements on a Thorium base, i.e. started in the Th/Pu fuel cycle, similarly to fast neutron reactors operated in the U/Pu fuel cycle. We will detail optimizations of this transition between the reactors of second and third generations to the Thorium cycle. Such a transition is based on a fleet of TMSRs with no moderator in the core, including TMSRs started with Plutonium and TMSRs directly started with 233U. We developed parametric studies to optimize these TMSRs, amongst which the study presented here, based on one of the main TMSR parameters: the percentage of heavy nuclei in the fuel salt of the TMSR configuration, which modifies the moderation ratio of the reactor and thus influences both the initial fissile inventory and the spectrum of the reactor. We analyze the characteristics of each reactorconfiguration, in terms of deterministic safety parameters, fissile matter inventory, salt reprocessing, radiotoxicity and waste production, and finally deployment capacities.

International audience; Molten salt reactors, in the configuration presented here and called Thorium Molten Salt Reactor (TMSR), are particularly well suited to fulfil the criteria defined by the Generation IV forum, and may be operated in simplified and safe conditions in the Th/233U fuel cycle with fluoride salts. The characteristics of TMSRs based on a fast neutron spectrum are detailed in this paper, focusing on their excellent level of deterministic safety. We aimed at designing a critical TMSR able to burn the Plutonium and the Minor Actinides produced in the currently operating reactors, and consequently to convert this Plutonium into 233U. This leads to closing the current fuel cycle thanks to TMSRs started with transuranic elements on a Thorium base, i.e. started in the Th/Pu fuel cycle. We study the transition between the reactors of second and third generations to the Thorium cycle in a European frame.

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Les réacteurs à sels fondus semblent aujourd'hui présenter une alternative intéressante aux réacteurs de quatrième génération refroidis au sodium. En effet, les réacteurs à sels fondus ont beaucoup évolué depuis le M.S.B.R. (prototype américain de réacteur à sels fondus modéré au graphite et fonctionnant en spectre thermique). Le concept évolue aujourd'hui vers des réacteurs sans modérateur en coeur dont le spectre neutronique s'est considérablement durci par rapport au spectre thermique du M.S.B.R. Ces réacteurs possèdent une unité de retraitement couplée qui permet de purifier le sel et d'optimiser la gestion des déchets rejetés. On espère ainsi définir un retraitement efficace qui minimiserait la radiotoxicité de ce type de réacteur. Ce rapport explique comment on simule l'évolution des réacteurs à sels fondus et on calcule la radiotoxicité des déchets produits. Les résultats donnés ici ne sont qu'indicatifs et servent surtout à monter que les outils et méthodes développés pendant ce stage sont satisfaisants et permettront une étude beaucoup plus poussée lors de la thèse qui suit.

The tie lines delineating equilibria between different oxides of the Ca-Al-O system and liquid Ca-Al alloy has been determined at 1373 K. Equilibration of the alloy with two adjacent oxide phases in the CaO-Al2O3 pseudo-binary system was established in a closed cell made of iron. Equilibrium oxide phases were confirmed by x-ray analysis and alloy compositions were determined by chemical analysis. The compound 12CaO.7Al2O3 Ca12Al14O33 was found to be a stable phase in equilibrium with calcium alloys. The experimental diagram is consistent with that calculated from the free energies of formation of the oxide phases and activities in liquid Ca-Al alloys at 1373 K reported in the literature.