Safe-to-fail: Accident-tolerant fuel cladding

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Conventional water-cooled nuclear reactors, including the current fleet of CANDU reactors and the small modular reactor (SMR) planned for construction at the Darlington nuclear power plant site, use uranium oxide fuel that is clad in protective tubes of a zirconium-tin alloy called Zircaloy. However, during a severe loss-of-coolant accident (LOCA) in a reactor, the reaction of the Zircaloy with high-temperature steam can generate large volumes of hydrogen, a gas that is explosive when mixed with air. Such a scenario previously played out during the Fukushima-Daiichi reactor accident in 2011, resulting in multiple hydrogen explosions. A variety of "accident tolerant fuel" (ATF) concepts have been explored to help decrease or eliminate the risk of cladding-steam reactions leading to hydrogen explosions under severe LOCA conditions. Much of this research has focused on either applying a protective coating to the Zircaloy to decrease its reactivity with steam under severe LOCA conditions or replacing Zircaloy with a material that would not react so dangerously during an accident. Unfortunately, the current suite of coatings and replacements are not durable enough to withstand a LOCA without significant degradation. Since Canada is now preparing to build new SMRs, there is considerable value in building expertise in ATF cladding to match that of other leading countries, such as the USA, France, and China. This knowledge will be particularly valuable for government decision-making and regulatory oversight and licensing of SMR construction and operation. The European Parliament has recently mandated that all reactors implement ATFs approved by their respective country's regulators in order to qualify as "green energy" sources. Implementing such policy and regulatory decisions in Canada will require a robust domestic understanding of the various factors related to ATF cladding performance, established by studying existing ATF cladding concepts and developing novel Canadian solutions. This research program aims to develop novel ATF claddings and to perform fundamental studies on existing ATF cladding concepts meant to eliminate the potential for hydrogen explosions during a severe LOCA.