## 1 Introduction  
The development of nuclear fission waste reduction and management strategies has been of interest for several decades. The first strong development push was affected by two important international projects on partitioning and transmutation (P&T) of transuranium isotopes active in the late 1980s and early 1990s: the OMEGA (Options for Making Extra Gains from Actinides and fission products) programme in Japan and the CAPRA/CADRA programme in France. The former [1], the first major P&T project, arose from the Japan Atomic Energy Commission's October 1988 report entitled \"Long-Term Program for Research and Development on Nucleide Partitioning and Transmutation (P&T)\", which considered the conversion of High-Level Waste (HLW) into useful resources and the improvement of HLW disposal efficiency. As well as the OMEGA programme, this report plotted a course for technological development up to the year 2000. The French CAPRA/CADRA projects (CAPRA stands for Combustion Amelioree du Plutonium dans les Reacteurs Avances or increased plutonium consumption in advanced reactors, whilst CADRA stands for Consomomation d'Actinides et de Dechets dans les Reacteurs Avances or consumption of actinides and waste in advanced reactors) were then established in 1991 by French law; this mandated a combined 15-year research programme to investigate the technical options available to the nuclear fuel cycle in France [2] with the intention of investigating future options to apply fast reactors, originally foreseen for power production, to the burnup of excess plutonium, actinides and waste. Therefore, while the OMEGA project focused on partitioning, as well as on transmutation, the CAPRA/CADRA project was originally only dedicated to transmutation, with a major focus of this and related reactor studies being the reuse and incineration of Plutonium in the Superphenix prototype fast breeder reactor. Different aspects of the potential of fast reactor systems to be used for the burning of plutonium and minor actinides (MAs) (Np, Am, Cm) were considered in CAPRA and CADRA projects, with CAPRA mainly dealing with managing the plutonium stockpile and CADRA considering the burning (transmutation) of MAs and long-lived fission products [3]. As a consequence, waste management through P&T has mainly since been seen as a distinct task requiring a separate/special type of reactor system. More recently the potential for bringing fast reactors into operation both for widespread power production and waste management has been explored. This has very often used a so-called double strata approach [4; 5; 6] with sodium cooled fast reactors being proposed as the stratum (or tier) 1 system to produce energy from Plutonium and with a specific stratum/ tier 2 system, e.g., an accelerator driven system (ADS) or critical solid fuelled fast reactor [5], used to efficiently burn the remaining waste (low quality plutonium and minor actinides) [6]. Now, this same approach is being followed in the recently established Russian P&T programme, but in contrast to the European programmes the Russian effort plans to use a molten salt fast reactor as its tier 2 burner system [7; 8]. More generally, a question can now be posed: is it really necessary to have a two separated tiers approach, or would it not be possible and more conveniently go to a novel breakthrough technology, where both tiers are merged together which would in turn generate a market opportunity to deliver energy production and waste management in one integrated reactor system? Given today's vastly different energy landscape, compared to the 1990s when P&T was emerging, future energy technologies have to address the urgent challenges of net zero and sustainable energy research and development, the energy trilemma and the meeting of the UN sustainable development goals (SDGs).