What is the future for nuclear fission technology? A technical opinion from the Guest Editors of VSI NFT series and the Editor of the Journal Nuclear Engineering and Design

The Nuclear Fission Technology (NFT) series of Virtual Special Issues (VSIs) for the Journal Nuclear Engineering and Design (J NED) was proposed in 2023, including the request to potential authors of manuscript to address the following questions: o For how long will (water-cooling based) large size nuclear reactor survive? o Will water-technology based SMRs displace large reactors? o Will non-water-cooling technology SMRs and micro-reactors have an industrial deployment? o Will breeding technology, including thorium exploitation, have due relevance? o Will ‘nuclear infrastructure’ (fuel supply, financial framework, competence by regulators for new designs, waste management, etc.) remain or be sufficiently robust? Several dozen Guest Editors (GEs), i.e., the authors of the present document, managed the activity together with the Editor-in-Chief (EiC) of the journal. More than one thousand scientists contributed 470+ manuscripts, not evenly distributed among the geographical regions of the world and not necessarily addressing directly the bullet-questions, but certainly providing a view of current research being done. Key conclusions are as follows: (a) Large size reactors are necessary for a sustainable and safe exploitation of nuclear fission technology; (b) The burning of 233U (from thorium) and 239Pu (from uranium) is unavoidable, as well as recycling residual uranium currently part of waste; (c) Nuclear infrastructures in countries that currently use, or are entering the use of, fission energy for electricity production need a century planning; (d) The adoption of small reactors for commercial naval propulsion, hydrogen production and desalination is highly recommended.