[en] Within the frame of development of sustainable nuclear programs, this report does not only deal with the development of nuclear systems, but with the general context in which such a development will occur. While describing and commenting her professional career in different nuclear research institutions and on various research programs, the author describes the assets and challenges of the electro-nuclear sector, and then focuses on the research structures and contexts for future possible nuclear concepts, and more particularly like melted salt reactors for which she highlights scientific and technical problems which are still to be solved. She describes French, European and world programs which were to start by 2009

[en] Highlights: • Neutronic calculations for fast spectrum molten salt reactor. • Evaluation of the fissile matter to be used in such reactor as initial fissile load. • Capabilities to transmute transuranic elements. • Deployment scenarios of the Thorium fuel cycle. • Waste management optimization with molten salt fast reactor. - Abstract: There is currently a renewed interest in molten salt reactors, due to recent conceptual developments on fast neutron spectrum molten salt reactors (MSFRs) using fluoride salts. It has been recognized as a long term alternative to solid-fueled fast neutron systems with a unique potential (large negative temperature and void coefficients, lower fissile inventory, no initial criticality reserve, simplified fuel cycle, wastes reduction etc.) and is thus one of the reference reactors of the Generation IV International Forum. In the MSFR, the liquid fuel processing is part of the reactor where a small side stream of the molten salt is processed for fission product removal and then returned to the reactor. Because of this characteristic, the MSFR can operate with widely varying fuel compositions, so that the MSFR concept may use as initial fissile load, ²³³U or enriched uranium or also the transuranic elements currently produced by light water reactors. This paper addresses the characteristics of these different launching modes of the MSFR and the Thorium fuel cycle, in terms of safety, proliferation, breeding, and deployment capacities of these reactor configurations. To illustrate the deployment capacities of the MSFR concept, a French nuclear deployment scenario is finally presented, demonstrating that launching the Thorium fuel cycle is easily feasible while closing the current fuel cycle and optimizing the long-term waste management via stockpile incineration in MSRs

[en] Highlights: • Neutronic ‘Transient Fission Matrix’ approach coupled to the CFD OpenFOAM code. • Fission Matrix interpolation model for fast spectrum homogeneous reactors. • Application for coupled calculations of the Molten Salt Fast Reactor. • Load following, over-cooling and reactivity insertion transient studies. • Validation of the reactor intrinsic stability for normal and accidental transients. - Abstract: In this paper we present transient studies of the Molten Salt Fast Reactor (MSFR). This generation IV reactor is characterized by a liquid fuel circulating in the core cavity, requiring specific simulation tools. An innovative neutronic approach called “Transient Fission Matrix” is used to perform spatial kinetic calculations with a reduced computational cost through a pre-calculation of the Monte Carlo spatial and temporal response of the system. Coupled to this neutronic approach, the Computational Fluid Dynamics code OpenFOAM is used to model the complex flow pattern in the core. An accurate interpolation model developed to take into account the thermal hydraulics feedback on the neutronics including reactivity and neutron flux variation is presented. Finally different transient studies of the reactor in normal and accidental operating conditions are detailed such as reactivity insertion and load following capacities. The results of these studies illustrate the excellent behavior of the MSFR during such transients.

[en] In the MSFR (Molten Salt Fast Reactor), the liquid fuel processing is part of the reactor where a small side stream of the molten salt is processed for fission product removal and then returned to the reactor. Because of this design characteristic, the MSFR can thus operate with a widely varying fuel composition. Our reactor's studies of the MSFR concept rely on numerical simulations making use of the MCNP neutron transport code coupled with a code for Bateman's equations computing the population of any nucleus inside any part of the reactor at any moment. The classical Bateman's equations have been modified by adding 2 terms representing the reprocessing capacities and an online addition. We have thus coupled neutronic and reprocessing simulation codes in a numerical tool used to calculate the extraction efficiencies of fission products, their location in the whole system and radioprotection issues. The very preliminary results show the potential of the neutronic-reprocessing coupling we have developed. We also show that these studies are limited by the uncertainties on the design and the knowledge of the chemical reprocessing processes. (A.C.)

[en] Starting from the Molten Salt Breeder Reactor project of Oak-Ridge, an innovative concept called Molten Salt Fast Reactor or MSFR based on a fast neutron spectrum has been proposed, resulting from extensive parametric studies in which various core arrangements, reprocessing performances and salt compositions were investigated to adapt the reactor in the framework of the deployment of a thorium based reactor fleet on a worldwide scale. In the MSFR, the liquid fuel processing is part of the reactor where a small side stream of the molten salt is processed for fission product removal and then returned to the reactor. Because of this characteristic, the MSFR can operate with widely varying fuel compositions. Thanks to this fuel composition flexibility, the MSFR concept may use as initial fissile load, ²³³U or uranium or also the transuranic elements currently produced by light water reactors. This paper addresses the characteristics of these different launching modes of the MSFR and the Thorium fuel cycle, in terms of safety, proliferation, breeding, and deployment capacities of these reactor configurations. To illustrate the deployment capacities of the MSFR concept, a French nuclear deployment scenario is finally presented, demonstrating that launching the Thorium fuel cycle is easily feasible while closing the current fuel cycle and optimizing the long-term waste management. (authors)

[en] Starting from the Molten Salt Breeder Reactor project of Oak-Ridge, we have performed parametric studies in terms of safety coefficients, reprocessing requirements and breeding capabilities. In the frame of this major re-evaluation of the molten salt reactor (MSR), we have developed a new concept called Molten Salt Fast Reactor or MSFR, based on the Thorium fuel cycle and a fast neutron spectrum. This concept has been selected for further studies by the MSR steering committee of the Generation IV International Forum in 2009. Our reactor's studies of the MSFR concept rely on numerical simulations making use of the MCNP neutron transport code coupled with a code for materials evolution which resolves the Bateman's equations giving the population of each nucleus inside each part of the reactor at each moment. Because of MSR's fundamental characteristics compared to classical solid-fuelled reactors, the classical Bateman equations have to be modified by adding two terms representing the reprocessing capacities and the fertile or fissile alimentation. We have thus coupled neutronic and reprocessing simulation codes in a numerical tool used to calculate the extraction efficiencies of fission products, their location in the whole system (reactor and reprocessing unit) and radioprotection issues. (authors)

[en] There is currently a renewed interest in molten salt reactors, due to recent conceptual developments on fast neutron spectrum molten salt reactors (MSFRs) using fluoride salts. This concept, operated in the Thorium fuel cycle, may be started either with ²³³U, enriched U and/or TRU elements as initial fissile load. It has been recognized as a long term alternative to solid fuelled fast neutron systems with a unique potential (such as large negative temperature and void coefficients, lower fissile inventory, no initial criticality reserve, simplified fuel cycle, wastes reduction…) and is thus one of the reference reactors of the Generation IV International Forum. This paper will focus on recommendations to define a demonstrator representing the key points of the reference MSFR power reactor (3000 MWth, fuel salt volume of 18 m³). The MSFR demonstrator is designed to assess the technological choices of this innovative system (fuel salt, structural materials, fuel heat exchangers…). It seems finally possible to slightly modify such a demonstrator which could then be a self-breeder modular reactor. (author)

[en] Molten salt reactors are liquid-fueled reactors so that they are flexible in terms of operation (load-following capabilities...) or design (core geometry, fuel composition, specific power level...) choices, but they are very different in terms of design and safety approach compared to solid-fueled reactors. Such reactors call for a new definition of their operating procedures. Dedicated studies are performed in the frame of the European SAMOFAR (Safety Assessment of Molten Salt Fast Reactors) project of Horizon 2020. This paper focuses on the behavior of the MSFR fuel circuit in interaction with the intermediate circuit. It is devoted to the start-up procedure of the MSFR, including the description of the proposed procedure, a presentation of the approach to criticality and the reactivity measurement during the filling of the core, and finally studies of accident scenarios (overcooling, reactivity insertion) at low power during the divergence step of the MSFR, highlighting the very good behavior of the reactor to such abnormal transients. (author)

[en] CNRS has focused R&D efforts on the development of a new reactor concept called the Molten Salt Fast Reactor (MSFR), characterized by a circulating liquid fuel and a fast neutron spectrum. This paper presents the new design proposed for the fuel circuit in the frame of the SAMOFAR European project and focuses on the design studies of the emergency draining system of the MSFR. These new designs result from physical and preliminary safety studies such as optimizing the use of the molten salt both as fuel and coolant, defining the operating procedures or 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. (author)

[en] CNRS has focused R&D efforts on the development of a new reactor concept called the Molten Salt Fast Reactor (MSFR), characterized by a circulating liquid fuel and a fast neutron spectrum. This paper presents the new design proposed for the fuel circuit in the frame of the SAMOFAR European project and focuses on the design studies of the emergency draining system of the MSFR. These new designs result from physical and preliminary safety studies such as optimizing the use of the molten salt both as fuel and coolant, defining the operating procedures or 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. (author)