[en] Because of its energetic, environmental, economical, social, safety, political, and even ideological aspects, the nuclear energy is a major society stake. It is a technical and complex topic as well which merits a democratic, well argued and transparent debate. This book supplies to the reader all the necessary information for a thorough analysis of this much disputed energy source without any bias: why France is one of the most nuclearized country in the world? Can we get out of nuclear energy? How and at what price? Wastes and safety: what can we expect (or not) from the next generations of reactors? Should we have a referendum? In this book, two researchers of the nuclear domain, an economist and a journalist invite us to consider the problem from all angles. (J.S.)

[en] Molten salt reactors seem to be an alternative candidate to the classical fourth generation reactors such as the European Fast Reactor. Indeed molten salt reactors have changed since the Molten Salt Breeder Reactor (US molten salt reactor prototype, moderated with graphite). They could be reactors without graphite moderator which neutron spectrum reaches fast spectrum. Those kinds of reactors have a batch reprocessing plant which allows improvement in terms of radiotoxicity. This report presents how we can simulate correctly molten salt reactor together with the salt reprocessing. Results are indicative results to prove that methods are self-sufficient to carry out a good study. The complete study would be done during the next three years of my thesis. (authors)

[en] Molten Salt Reactors (MSRs) are one of the systems retained by Generation IV as a candidate for the next generation of nuclear reactors. This type of reactor is particularly well adapted to the thorium fuel cycle (Th- ²³³U) which has the advantage of producing less minor actinides than the uranium-plutonium fuel cycle (²³⁸U- ²³⁹Pu). In the frame of a major re-evaluation of the MSR concept and concentrating on some major constraints such as feasibility, breeding capability and, above all, safety, we have considered a particular reactor configuration that we call the 'unique channel' configuration in which there is no moderator in the core, leading to a quasi fast neutron spectrum. This reactor is presented in the first section. MSRs benefit from several specific advantages which are listed in a second part of this work. Beyond these advantages of the MSR, the level of the deterministic safety in such a reactor has to be assessed precisely. In a third section, we first draw up a list of the reactivity margins in our reactor configuration. We then define and quantify the parameters characterizing the deterministic safety of any reactor: the fraction of delayed neutrons, and the system's feedback coefficients that are here negative. Finally, using a simple point-kinetic evaluation, we analyze how these safety parameters impact the system when the total reactivity margins are introduced in the MSR. The results of this last study are discussed, emphasizing the satisfactory behavior of the MSR and the excellent level of deterministic safety which can be achieved. This work is based on the coupling of a neutron transport code called MCNP with a materials evolution code. The former calculates the neutron flux and the reaction rates in all the cells while the latter solves the Bateman equations for the evolution of the materials composition within the cells. These calculations take into account the input parameters (power released, criticality level, chemistry, etc.), by adjusting the neutron flux or the materials composition of the core on a regular basis. Our calculations are based on a precise description of the geometry and consider several hundreds of nuclei with their interactions and radioactive decay; they allow a thorough interpretation of the results. All the data discussed in this paper result from the evolution of the reactor over 100 years. (authors)

[en] 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 the non-moderated TMSR based on a fast neutron spectrum are detailed in this paper: we aimed at designing an optimised TMSR with the simplest configuration. Using a simple kinetic-point model, we analyze the reactor's transient as the total reactivity margins are introduced in the core. We thus confirm, beyond the classical advantages of molten salt reactors, the satisfactory behaviour of the TMSR in terms of safety and the excellent level of stability which can be achieved in such reactors. (authors)

[en] If we are to combat climate change significantly, massive use of nuclear energy is essential. This requires upstream management of the risks associated with nuclear power and its acceptability to society. Nuclear generation will also have to be able to keep up with the load of a fleet that includes a large proportion of renewable energies. This article presents and discusses a new approach to meeting these challenges: liquid fuel reactors, or molten salt reactors, which are attracting growing interest. It describes the developments made in France with the CNRS MSFR (molten salt reactor with fast neutron spectrum) concept, which offers prospects for the incineration of transuranics and the management of intermittent energy sources. (authors)

[en] Within the Generation-IV International Forum (GIF), research is performed on molten salt reactor (MSR) concepts. Two fast spectrum MSR are being studied, which are large power units with a homogeneous core: the two fluid 3000MWt MSFR in France, Euratom and Switzerland as well as the single fluid 2400 MWt MOSART in the Russian Federation. R&D studies are on-going in order to verify that fast spectrum MSR systems satisfy the goals of Generation-IV reactors in terms of sustainability, safety, waste management and non-proliferation. The IAEA defines proliferation resistance as a nuclear power system’s capacity to prevent the theft or undeclared production of nuclear material as well as difficulty in use of the technology in respect of procuring a nuclear weapon. GIF has proposed a methodology that should allow the analysis of proliferation resistance issues in systems under development. An initial application of this methodology to the MSFR and MOSART is presented here, including an analysis of both the reactor plant and the fuel processing units, these being located in-situ in these concepts. For this initial study, we have focused our attention on a portion of the methodology retained by GIF. This consists of defining a threat, then analyzing the system’s response by identifying: the system elements; the targets involved and the pathways for achieving the proliferant objectives. Counter measures are then proposed as obstacles on the pathways identified. Because the MSFR and MOSART are in the design phase, we have adopted a gradual approach to the issues, focusing on the seemingly most dangerous situations. This first study case concentrates on the threat represented by a State that wishes to acquire nuclear weapons, and plans to obtain nuclear material from a power plant site based on MSFR and MOSART reactor plants and subsequently process the nuclear material in a concealed installation. More specifically, this study focuses on the threat that fissile material be diverted in such a situation. The purpose of the paper is to work out design recommendations for the elements of the system. (author)

[en] The Molten Salt Fast Reactor (MSFR) with its liquid circulating fuel and its fast neutron spectrum calls for a new safety approach including technological neutral methodologies and analysis tools adapted to early design phases. In the frame of the Horizon2020 program SAMOFAR (Safety Assessment of the Molten Salt Fast Reactor) a safety approach suitable for Molten Salt Reactors is being developed and applied to the MSFR. After a description of the MSFR reference design, this paper focuses on the identification of the Postulated Initiating Events (PIEs), which is a core part of the global assessment methodology. To fulfil this task, the Functional Failure Mode and Effect Analysis (FFMEA) and the Master Logic Diagram (MLD) are selected and employed separately in order to be as exhaustive as possible in the identification of the initiating events of the system. Finally, an extract of the list of PIEs, selected as the most representative events resulting from the implementation of both methods, is presented to illustrate the methodology and some of the outcomes of the methods are compared in order to highlight symbioses and differences between the MLD and the FFMEA

[en] The contributions addressed the following issues: The ability of nuclear energy to limit global warming; The Astrid project; The Integral Fast Reactor; The fuel (UOX and MOX) cycle in the French fleet; The Molten Salt Fast reactor (MSFR); The steady salt reactor; SMRs, MSRs and SMMSRs (small reactors); Thorium or the Poulidor of the nuclear (the best finishes second); Description, comparison and trends of third-generation reactors; The constraints of network equilibrium and the limitation for the integration of renewable energies; Are nuclear and renewable energies complementary or substitute to one another

[en] Liquid-fuelled molten salt reactors (MSRs) may be different in terms of design, operation and safety issues compared to large water-cooled nuclear power plants (NPPs). This paper presents in a first part an analysis of the safety paradigm for such systems, based on the identification of safety-related innovations of such MSRs. The second part of the article is dedicated to an application to the Molten Salt Fast Reactor (MSFR) concept developed in France by CNRS to illustrate the safety principles application on a specific design representative of similar liquid-fuelled MSRs.

[en] As new space missions are planned, longer and more ambitious, the need for a controllable powerful energy becomes a priority. Though electric propulsion still suffers from its very low thrust, advanced designs like NASA's X3 or Ad Astra Rocket Company's VASIMR are filling the gap at the price of a great power supply need. Given this context, we began the study of a 1 MWe reactor for space application. Because of its inherent safety, as well as its high controllability allowing quick power changes, we choose the molten salt reactor technology. The presented work relates to the building of the core design based on the technology of molten salt reactors, already taking into account technological and safety constraints. Initial calculations motivated the choice of a thermal graphite-moderated reactor using a U²³⁵ highly enriched fluoride salt. A study of different configurations and the sensibility of the criticality to some variations of the design, as well as some identified constraints on the system, then oriented the work toward the proposed design. Once a design chosen, the reactivity reserve and the Doppler effect compensation have been studied. This last point is essential to ensure an autonomous start-up of the core, an easier design and the possibility to shut-down and restart the reactor several times as a solid salt means no density negative feedback. Otherwise, the core could not reach on its own its operating temperature without an additional and independent core heater system to melt the salt. Eventually lifespan issues through Monte-Carlo burn-up calculations on the proposed design have been investigated. (authors)