Development and validation of Loss of Coolant Accident (LOCA) simulation capability in the ENIGMA fuel performance code for zirconium-based cladding materials

Loss-of-coolant accident (LOCA) modelling forms a pivotal element in the licensing of light water reactor technologies. Within this context, the National Nuclear Laboratory has further developed its ENIGMA fuel performance code to accurately simulate fuel behaviour during limiting design-basis accidents. The enhanced ENIGMA code now incorporates models for high-temperature cladding creep, cladding oxidation and hydriding at elevated temperatures, cladding phase change, and cladding failure. A detailed examination of existing LOCA-capable models relevant to industrial-standard fuel performance codes was conducted, which led to the introduction of an industrial state-of-the-art capability within ENIGMA for modelling uranium dioxide fuel in various zirconium alloy cladding materials. The efficacy of the enhanced ENIGMA code was validated using data from the IFA-650.10 LOCA experiment carried out as part of the OECD Halden Reactor Project. ENIGMA's predictions were compared with both the experimental data and predictions of other fuel performance codes from the International Atomic Energy Agency's Fuel Modelling in Accident Conditions (FUMAC) coordinated research project. The comparison generally showed good agreement, highlighting the effectiveness of the improved ENIGMA code.