Accident Tolerant Fuels (ATF) for present operating reactors

All light water reactors (LWRs) around the world today are using fuel systems comprised of uranium oxide (UO2) within a zirconium-based alloy cladding. Some reactors use uranium-plutonium oxide fuels, which are also known as mixed oxide (MOX) fuels. The oxide fuel-zircaloy system has been optimised over many decades and performs very well under normal operating conditions and anticipated transients. However, because of the highly exothermic, auto-cathalitic zirconium-steam reactions above 1200°C, which can occur under some low frequency accidents – when core cooling is temporarily lost and part of the core is uncovered – low probability accidents may lead to an excess generation of heat and hydrogen, resulting in undesirable core damage.
Although relatively small scale Accident Tolerant Fuel R&D programs were existing under the US -DOE guidance in 2009, the 2011 Great East Japan Earthquake and Tsunami, and the events that followed at the Fukushima Daiichi power plant, greatly expanded global interest in exploring fuels with enhanced performance during such rare events, with the ATF acronym as Accident Tolerant Fuel development programmes “exploding” in available funding, size and efforts in many research institutions and industry teams. The 2023 European Taxonomy requirements also explicitly demanded for nuclear reactors to be fueled with Accident Tolerant Fuels.
While there is broad consensus that a new fuel system alone is insufficient to mitigate accident consequences and full tolerance to severe accident conditions seems rather utopic, fuel in combination with other systems may provide some relief in responding to such rare events, while providing additional benefits during more frequent events and/or normal operations. The recent mindset therefore seems to evolve towards ATF as Advanced Technology Fuels with improving safety margins and improved thermo-mechanical performance.
Presentation material
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