Molten Salt Reactor to close the fuel cycle: example of MSFR multi-recycling applications

International audienceOn 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