A solution for the nuclear waste problem is the key challenge for an extensive use of nuclear reactors as a major carbon free, sustainable, and applied highly reliable energy source. Partitioning and Transmutation (P&T) promises a solution for improved waste management. Current strategies rely on systems designed in the 60’s for the massive production of plutonium. We propose an innovative strategic development plan based on invention and innovation described with the concept of developments in s-curves identifying the current boundary conditions, and the evolvable objectives. This leads to the ultimate, universal vision for energy production characterized by minimal use of resources and production of waste, while being economically affordable and safe, secure and reliable in operation. This vision is transformed into a mission for a disruptive development of the future nuclear energy system operated by burning of existing spent nuclear fuel (SNF) without prior reprocessing. This highly innovative approach fulfils the sustainability goals and creates new options for P&T. A proof on the feasibility from neutronic point of view is given demonstrating sufficient breeding of fissile material from the inserted SNF. The system does neither require new resources nor produce additional waste, thus it provides a highly sustainable option for a future nuclear system fulfilling the requests of P&T as side effect. In addition, this nuclear system provides enhanced resistance against misuse of Pu and a significantly reduced fuel cycle. However, the new system requires a demand driven rethinking of the separation process to be efficient.

There is growing interest in the use of advanced reactor systems for powering industrial processes which could significantly help to reduce CO ${}_2$ emissions in the global energy system. However, there has been limited consideration into the role nuclear power would play in meeting current and future industry heat demand, especially with respect to the advantages and disadvantages nuclear power offers relative to other competing low-carbon technologies, such as Carbon Capture and Storage (CCS). In this study, the current market needs for high temperature heat are considered based on UK industry requirements and work carried out in other studies regarding how industrial demand could change in the future. How these heat demands could be met via different nuclear reactor systems is also presented. Using this information, it was found that the industrial heat demands for temperature in the range of 500 ${}^{\circ }$ C to 1000 ${}^{\circ }$ C are relatively low. Whilst High Temperature Gas-cooled Reactors (HTGRs), Very High Temperature Reactors (VHTRs), Gas-cooled Fast Reactors (GFRs) and Molten Salt Reactors (MSRs) have an advantage in terms of capability to achieve higher temperatures (>500 ${}^{\circ }$ C), their relative benefit over Liquid Metal-cooled Fast Reactors (LMFRs) and Light Water Reactors (LWRs) is actually smaller than previous studies indicate. This is because, as is shown here, major parts of the heat demand could be served by almost all reactor types. Alternative (non-nuclear) means to meet industrial heat demands and the indirect application of nuclear power, in particular via producing hydrogen, are also considered. As hydrogen is a relatively poor energy carrier, current trends indicate that the use of low-carbon derived hydrogen is likely to be limited to certain applications and there is a focus in this study on the emerging demands for hydrogen.

The current generation of nuclear reactors are evolutionary in design, mostly based on the technology originally designed to power submarines, and dominated by light water reactors. The aims of the Generation IV consortium are driven by sustainability, safety and reliability, economics, and proliferation resistance. The aims are extended here to encompass the ultimate and universal vision for strategic development of energy production, the “perpetuum mobile”—at least as close as possible. We propose to rethink nuclear reactor design with the mission to develop an innovative system which uses no fresh resources and produces no fresh waste during operation as well as generates power safe and reliably in economic way. The results of the innovative simulations presented here demonstrate that, from a theoretical perspective, it is feasible to fulfil the mission through the direct reuse of spent nuclear fuel from currently operating reactors as the fuel for a proposed new reactor. The produced waste is less burdensome than current spent nuclear fuel which is used as feed to the system. However, safety, reliability and operational economics will need to be demonstrated to create the basis for the long term success of nuclear reactors as a major carbon free, sustainable, and applied highly reliable energy source.

The electricity market is undergoing significant change with the increasing deployment of Variable Renewable Energy Sources (VRES) and the adoption of policies to electrify transport, heating and industry, which will continue to increase demands on all conventional power plants including nuclear. The increase in VRES also puts additional emphasis on services such as inertia and frequency response that only conventional plants, including nuclear, are readily able to meet. This study discusses what factors limit the ability of nuclear power plants to provide flexible response and how the UK nuclear power plants might be affected by the changes in future demand profiles. The study focuses on what impact there will be on current Pressurised Water Reactor (PWR) plants, though it also considers Small Modular Pressurised Water Reactor plants which might offer benefits with respect to improved power manoeuvrability. The main finding is that the most important attribute is the minimum power level for long-term operation, followed by the speed at which the plants can be brought online (that is, both start-up rate and ramp rate during power operation). With respect to both of these attributes, new build future PWR plants could potentially achieve large and rapid power changes by dumping part of the steam directly into the condenser, bypassing the steam turbine. Discussions with plant operators highlighted that there is currently limited demand for flexible operation in the UK from nuclear plants when other power plants are readily available to partake in flexible operation. The lack of any requirement for nuclear plants to operate flexibly means that the UK lags behind France, for example, which has much more experience in nonstationary operation of nuclear power plants. The paper also draws attention to the fact that with increasing VRES, there will be fewer plants able to provide rotational inertia and therefore more emphasis on the role the remaining plants (which include nuclear) can play in maintaining grid stability.

The energy trilemma forms the key driver for the future of energy research. In nuclear technologies, molten salt reactors are an upcoming option which offers new approaches. However, the key would be closed fuel cycle operation which requires sufficient breeding for a self-sustained long term operation ideally based on spent fuel. To achieve these attractive goals two challenges have been identified: achieving of sufficient breeding and development of a demand driven salt clean up system. The aim is to follow up on previous work to create an initial approach to achieving sufficient breeding. Firstly, identification of a salt system with a high solubility for fertile material and sufficiently low melting point. Secondly, evaluation of the sensitivity of the breeding performance on the sort of fissile material, the fissile material loading, and the core dimension all based on a realistic salt system which provides the solubility for sufficient fertile material to achieve the required breeding in a homogeneous reactor without breeding blanket. Both points are essential to create an innovative solution to harvest the fruits of a closed fuel cycle without the penalty of the prohibitively huge investments. It is demonstrated that the identified and investigated NaCl-UCl based systems are feasible to deliver the requested in-core breeding within the given solubility limits of fertile material in the salt system using either uranium as start-up fissile component or plutonium. This result is enriched by the analysis of the achievable full power days per inserted mass of plutonium. These new insights support reactor optimization and lead to a first conclusion that systems with lower power density could be very attractive in the case of low fuel cost, like it would be given when operating on spent nuclear fuel.

The PUREX technology based on aqueous processes is currently the leading reprocessing technology in nuclear energy systems. It seems to be the most developed and established process for light water reactor fuel and the use of solid fuel. However, demand driven development of the nuclear system opens the way to liquid fuelled reactors, and disruptive technology development through the application of an integrated fuel cycle with a direct link to reactor operation. The possibilities of this new concept for innovative reprocessing technology development are analysed, the boundary conditions are discussed, and the economic as well as the neutron physical optimization parameters of the process are elucidated. Reactor physical knowledge of the influence of different elements on the neutron economy of the reactor is required. Using an innovative study approach, an element priority list for the salt clean-up is developed, which indicates that separation of Neodymium and Caesium is desirable, as they contribute almost 50% to the loss of criticality. Separating Zirconium and Samarium in addition from the fuel salt would remove nearly 80% of the loss of criticality due to fission products. The theoretical study is followed by a qualitative discussion of the different, demand driven optimization strategies which could satisfy the conflicting interests of sustainable reactor operation, efficient chemical processing for the salt clean-up, and the related economic as well as chemical engineering consequences. A new, innovative approach of balancing the throughput through salt processing based on a low number of separation process steps is developed. Next steps for the development of an economically viable salt clean-up process are identified.