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Abstract The grand challenge of “net-zero carbon” emission calls for technological breakthroughs in energy production. The traveling wave reactor (TWR) is designed to provide economical and safe nuclear power and solve imminent problems, including limited uranium resources and radiotoxicity burdens from back-end fuel reprocessing/disposal. However, qualification of fuels and materials for TWR remains challenging and it sets an “end of the road” mark on the route of R&D of this technology. In this article, a novel approach is proposed to maneuver reactor operations and utilize high-temperature transients to mitigate the challenges raised by envisioned TWR service environment. Annular U-50Zr fuel and oxidation dispersion strengthened (ODS) steels are proposed to be used instead of the current U-10Zr and HT-9 ferritic/martensitic steels. In addition, irradiation-accelerated transport of Mn and Cr to the cladding surface to form a protective oxide layer as a self-repairing mechanism was discovered and is believed capable of mitigating long-term corrosion. This work represents an attempt to disruptively overcome current technological limits in the TWR fuels. Impact statement After the Fukushima accident in 2011, the entire nuclear industry calls for a major technological breakthrough that addresses the following three fundamental issues: (1) Reducing spent nuclear fuel reprocessing demands, (2) reducing the probability of a severe accident, and (3) reducing the energy production cost per kilowatt-hour. An inherently safe and ultralong life fast neutron reactor fuel form can be such one stone that kills the three birds. In light of the recent development findings on U-50Zr fuels, we hereby propose a disruptive, conceptual metallic fuel design that can serve the following purposes at the same time: (1) Reaching ultrahigh burnup of above 40% FIMA, (2) possessing strong inherent safety features, and (3) extending current limits on fast neutron irradiation dose to be far beyond 200 dpa. We believe that this technology will be able to bring about revolutionary changes to the nuclear industry by significantly lowering the operational costs as well as improving the reactor system safety to a large extent. Graphical abstract

The performance of the droplets is vital of importance to the annular-mist flow and the heat transfer for the reflooding conditions. In this research, a two-fluid three-field model for the vertical upward flow is developed. The field equations of the vapor, continuous liquid phase and dispersed liquid droplet phase are established. The set of equations are solved by the semi-implicit difference algorithm based on the staggered grids. Wrutz's steam-water entrainment experiment is simulated to evaluate the performance of the selected closure relations. Becker's and Bennett's dryout and post-dryout heat transfer experiments are simulated to validated the interfacial and wall heat transfer models. Finally, the tubular reflooding experiments are simulated to study the effect of the droplets on the wall heat transfer for different injection conditions. The predicted results are compared to the experimental data and the predicted results by the additional two-fluid model. The results show that the predicted results by this two-fluid three-field model are more accurate than those by the additional two-fluid model.