Can materials innovation prevent another Fukushima?

Konstantina Lambrinou of the University of Huddersfield explains why the accelerated development of advanced nuclear materials is the shortest path to safer nuclear energy

The Fukushima Daiichi event in March 2011 demonstrated the need for safer nuclear energy, thus becoming a major driving force for global investments in accident-tolerant fuels (ATFs). The Fukushima event was caused by material failure, i.e., the melting of zirconium-based alloy (zircaloy) fuel claddings during the loss-of-coolant accident following the 2011 Great East Japan Earthquake and tsunami. The root cause of this failure lies in the runaway oxidation reactions of zircaloys in steam, which is the state of the primary coolant (water) of light water reactors during accidents. These reactions are strongly exothermic, producing copious amounts of heat that can quickly raise temperature, resulting in core meltdown, hydrogen explosion and release of radioactive fission products beyond the site boundary, as observed during the 2011 Fukushima event.

Such events are undesirable due to their detrimental effects on society and environment in the nuclear power plant (NPP) vicinity; moreover, the potential severity of nuclear accidents, albeit rare, discourages the widespread use of nuclear energy, a carbon-free energy that can reduce the greenhouse gas emissions of other energy sources and assist humanity in combatting climatic change. As the cause of Fukushima-like events lies in the inherent weaknesses of standard zircaloys, the development of ATF cladding materials that can outperform zircaloys is of paramount importance. The expedited deployment of ATF claddings will not only make nuclear energy safer by buying valuable time needed to resume control of NPPs during accident scenarios but will secure additional economic benefits stemming from the higher achievable levels of fuel burnup and enrichment due to the slower in-reactor corrosion of ATF claddings, thus resulting in longer fuel cycles, lower fuel costs, and better use of nuclear fuel before discarding it in waste.

The HORIZON SCORPION project

The HORIZON SCORPION project is a collaboration of sixteen partners from the EU, the UK, the USA, Japan and Switzerland that focuses on the “revolutionary” SiC/SiC composite ATF cladding material concept. SiC/SiC composites (i.e., SiC fibre-reinforced SiC) exhibit refractoriness (high-temperature stability), pseudo-ductility (damage tolerance; Fig. 1) and a lack of accelerated oxidation during a loss-of-coolant accident.

Despite these advantages, all state-of-the-art SiC/SiC composite variants must still overcome shortcomings such as the inadequate SiC compatibility with water and steam (Figs. 2-3). SCORPION strives for a radical improvement in the performance of SiC/SiC composites via multiscale material tailoring, which entails material re-design on the nanoscale (e.g., grain boundary engineering; Fig. 3), mesoscale (e.g., fibre/matrix interface modification) and macroscale (e.g., coating development) vis-à-vis the ATF application. Such extreme materials tailoring is foreign for the conservative nuclear sector; however, it is requested by the mounting needs in reliable nuclear materials. Accelerated material development (AMD) requires the incessant communication of design, production and performance assessment but is arguably a short and cost-effective path to safer nuclear energy. AMD draws inspiration from different scientific disciplines and uses sophisticated test tools/approaches that can recreate the conditions of the targeted application (Fig. 3).

^{Fig. 1: (a) Damage evolution in tough SiC/SiC composites under tension. The failure of these composites is graceful due to the weak fibre/matrix interface deflecting cracks. (b) Brittle failure of a monolithic SiC fibre starts from a critical flaw, forming three areas of increasing roughness (A: mirror; B: mist; C: hackle). (c) Tough failure of SiC/SiC composites showing fibre pullout.}

^{Fig. 2: (a) Damaged surface of a SiC/SiC composite tube surface during transient steam oxidation test to 1845°C. (b) Bubble formation following the melting of the silica oxide scale at around 1720°C.}

^{Fig. 3: (a) Setup for combined proton irradiation/aqueous corrosion tests on CVD SiC coatings used to protect SiC/SiC composites. (b) Tested CVD SiC was preferentially attacked at GBs and SFs. (c) Judicious GB engineering of SiC to improve its performance in water under irradiation.}

Prof Dr Konstantina Lambrinou is Professor of Advanced Materials at the School of Computing and Engineering, University of Huddersfield, UK. Her main research interests revolve around the accelerated development of advanced nuclear materials, including ATFs. Prof Lambrinou is the coordinator of HORIZON SCORPION (Grant Agreement No 101059511) and H2020 IL TROVATORE (Grant Agreement No 740415), the European lead of I-NERI PERSEUS, and the technical lead of a Westinghouse GAIN programme on the Cr-coated ATF cladding.

Further information
https://projectscorpion.eu
[email protected]

^{Acknowledgments: HORIZON SCORPION has received funding from the Euratom Research and Training Programme 2021-2025 under Grant Agreement No 101059511.}