Nuclear fission technologies have the potential to play a significant role in the energy mix of a net-zero and sustainable society. However, to achieve the sustainability goal two significant challenges remain: efficient and sustainable fuel usage and the minimization of long-term nuclear waste. Civil nuclear molten salt systems and technologies offer the opportunity to address both, delivering future reactors at scale for efficient and effective power production and nuclear waste burnup. Potentially, both objectives could be fulfilled in one reactor system, which could significantly improve sustainability indices. The key to this innovation is demand driven development of a significantly reduced fuel cycle with enhanced proliferation resistance which offers further potential for improvement. To achieve these goals, a transformative approach for salt clean-up during molten salt reactor operation is proposed, by concentrating on the detection and removal of key neutron poisoning elements which prevent the reactor from long-term operation. To enable this highly innovative development work, a novel analysis of the evolving elementary fuel composition, their concentrations, and their criticality influence is now provided in this work. This, combined with consideration of the oxidation states of each of these elements then provides the basis for the selection of these key poisons and the development of advanced separation processes and process monitoring. This work also discusses the importance of the effective integration of physics and chemistry when systems modelling in achieving these system development goals.

Molten salt reactors (MSRs), as one of the six main technologies of Gen IV, can meet the broad area of sustainability, economics, safety and reliability, proliferation resistance and physical protection goals. One of the main and first challenges in designing molten salt fast reactors (MSFRs) is the selection of an appropriate molten salt fuel system based on the envisaged applications and objectives. In this study’s series, a full-scope evaluation has been conducted about employing either chloride or fluoride salt fuels as the main competitors’ candidates for fuel salt in MSFR designs. Two distinguished projects, EVOL (CNRS, Grenoble-France), based on fluoride salt, and iMAGINE (The University of Liverpool, UK), based on chloride salts, were considered in order to achieve this goal as case studies. The first part of this series (part 1—this article) deals with the investigation of the thermophysical properties of the salt fuel system, criticality search and neutron-flux energy spectrum. An identical typical design of the MSFR core has been considered for a neutronic simulation by using MCNPX V2.7 based on the chemical composition of the fuel salt mentioned in both projects. The thermophysical evaluation has been conducted through literature research and theoretical methods based on the experimental values for the salt component properties. The results of the study are presented for thermophysical properties, including the melting point, vapour pressure/boiling point, specific heat capacity, thermal conductivity and density, in addition to neutronic simulation for the core critical dimension and neutron-flux spectrum of both the chloride- and fluoride-based salt fuel systems. In the discussion of the results, it is concluded that both the chloride and fluoride salt fuel systems have benefits that are seen on different comparative parameters. The delivered data will provide future decision makers with evidence for the salt choice for balancing their design objectives with the opportunities and expectations. Thus, a final selection of the most appropriate salt fuel system to be used in MSFRs will be postponed for more investigation in the final part of this article series, combining the data with different potential user profiles.

Nuclear technologies have the potential to play a major role in the transition to a global net-zero society. Their primary advantage is the capability to deliver controllable 24/7 energy on demand. However, as a prerequisite for successful worldwide application, significant innovation will be required to create the nuclear systems of the 21st century, the need of the hour. The pros (low harmful emissions, high reliability, low operational expenses, and high energy density) and cons (environmental damage, fuel waste disposal concerns, limited uranium reserves, and long construction time-frame) of nuclear are discussed and analysed at different levels—the societal and public recognition and concerns (accidents, weapons, mining, and waste) as well as the scientific/engineering and economic level—to assure a demand-driven development. Based on the analysis of the different challenges, a vision for the nuclear system of the 21st century is synthesised consisting of three pillars—unlimited nuclear energy, zero waste nuclear, and accident-free nuclear. These three combined visions are then transformed into dedicated and verifiable missions that are discussed, in detail, regarding challenges and opportunities. In the following, a stepwise approach to the development of such a highly innovative nuclear system is described. Essential steps to assure active risk reduction and the delivery of quick progress are derived as answers to the critique on the currently observed extensive construction time and cost overruns on new nuclear plants. The 4-step process consisting of basic studies, experimental zero power reactor, small-scale demonstrator, and industrial demonstrator is described. The four steps, including sub-steps, deliver the pathway to a successful implementation of such a ground-breaking new nuclear system. The potential sub-steps are discussed with the view not only of the scientific development challenges but also as an approach to reduce the regulatory challenges of a novel nuclear technology.

Nuclear technologies have the potential to play a unique role in delivering low carbon energy for a future net-zero society. However, for long-term success, nuclear technologies will need to deliver innovative solutions as proposed in iMAGINE. One of the key challenges for the envisaged highly integrated nuclear energy system is the need for a demand-driven salt clean-up system. The work described provides an insight into the interplay between a potential salt clean-up system and the reactor operation in a dynamic approach. The results provided will help to optimise the parameters for the salt clean-up process by delivering a dynamically calculated priority list, identifying the elements with great influence on reactor operation. The integrated model is used to investigate the ideal time for the initiation of the clean-up as well as the effect of different throughputs through the clean-up system on criticality as well as on the concentration of the elements in the reactor salt. Finally, a staggered approach is proposed with the idea to phase in the chemical clean-up processes step by step to keep the reactor critical. The results provide an essential step for the progress of iMAGINE as well as a basis for the interdisciplinary work required to bring iMAGINE into real operation.

Traditionally, there has been a gap between reactor operation and the consideration of nuclear waste in the final disposal. Fuel is produced, and fuel must be disposed. In the view of the reactor operator, fuel has to be cleaned in the reprocessing, and new solid fuel has to be produced in the view of the chemist. iMAGINE is designed to overcome this separation through a breakthrough development applying an optimized, integrative approach from cradle to grave of nuclear energy production as a first step to come as close as possible to the vision of zero waste nuclear power. It is described here for the first time in three steps: reactor, fuel cycle, and waste, providing the rationality behind each of the choices made to come to the overall solution to open the discussion and thinking process on what could be achieved by a very innovative approach to integrated nuclear energy production. The opportunities regarding the handling of the remaining waste are discussed with a view on the expectation of the final disposal community, the study “Nuclear waste from small modular reactors”, and the IAEA report “waste from innovative types of reactors and fuel cycles—a preliminary study”. The aim of this work is not to find answers to each of the raised points, but to identify potential approaches and promising ways to go, as well as to stimulate a discussion among experts. In the best case, this could lead to a change of track for nuclear power to become even more sustainable and an important, trusted technology to help solve the net-zero challenge.