MAX-phase coated claddings for light water reactor accident-tolerant fuels: corrosion stability, thermo-mechanical compatibility, irradiation effects, and deployment prospects

Following the Fukushima Daiichi accident, considerable effort has been directed toward accident-tolerant fuel claddings that can provide larger safety margins during normal operation, transients, and loss-of-coolant accidents. MAX phases, including Ti3SiC2, Ti2AlC, Cr2AlC, and Zr2AlC, have attracted interest for this purpose because they combine relatively high thermal conductivity, good mechanical strength, damage tolerance, and resistance to oxidation and irradiation. However, their behavior in light-water reactor environments is still not fully understood. In particular, questions remain regarding corrosion in reactor primary water, bonding and compatibility with zirconium alloys, irradiation-assisted degradation, and the feasibility of industrial-scale fabrication. This review discusses MAX-phase coatings and bulk MAX-phase cladding concepts for light water reactors, with particular attention paid to corrosion in a simulated primary coolant at 300–330 °C, where long-term performance strongly depends on the formation and stability of protective oxide scales. The reported degradation mechanisms and thermo-mechanical issues associated with coating zirconium substrates are examined. The performance of MAX phases is also compared with that of other candidate cladding materials in terms of oxidation kinetics, radiation resistance, fabrication routes, mechanical properties, and technological maturity. Multilayer coatings based on MAX phases combined with chromium or silicon layers are also discussed. Important open questions remain, particularly regarding hydrothermal degradation, radiation-damage evolution, and diffusion at the coating-substrate interface.