Fuel performance modelling of Cr-coated Zircaloy cladding under DBA/LOCA conditions

• TRANSURANUS and FRAPTRAN-TUmech have been extended to the simulation of Cr-coated Zircaloy. • The performance of coated and uncoated cladding has been assessed under two LOCA tests. • The independent modelling of coating and cladding is recommended. • The impact of the coating properties other than creep are negligible in terms of burst time. • The superior thermal creep resistance of coated cladding slightly delays the time of burst. Chromium coatings are being developed for advanced technology fuel (ATF) claddings, offering negligible corrosion during normal operation, improved resistance to high-temperature steam oxidation, and superior high-temperature strength, the latter two being of utmost relevance during design basis accidents (DBAs). Demonstrating the improved response of Cr-coated Zircaloy requires the development or extension of fuel performance codes to coating simulations. In this work, material models and correlations for Cr-coated Zircaloy cladding have been derived or obtained from the literature and implemented into TRANSURANUS and the FRAPTRAN-TUmech suite. These extended tools have been used to simulate two complementary LOCA tests: QUENCH-L1 rod 4 (out-of-pile bundle test on fresh Zircaloy cladding) and IFA-650.10 (in-pile single rod test on high-burnup Zircaloy-UO 2 fuel), enabling a gradual cross-verification of results between codes and a comparative performance analysis between coated and uncoated cladding. The results indicate negligible impact of coating properties other than creep on the burst time. While the superior high-temperature creep resistance of coated cladding slightly delays the burst time, additional burst data would be necessary to draw sound conclusions on the balloon size. Regarding the modelling approach, treating the coated cladding as a composite material through the definition of effective properties might result in worse performance relative to uncoated cladding, contradicting experimental observations. Therefore, the separate modelling of the coating and the cladding is recommended.