Validation of SARAX code system using the SFR operational tests

•The extended validation works on SARAX code based on the hot state data of two sodium-cooled fast reactors have been done.•The isothermal temperature coefficient and burnup reactivity swing of JOYO reactor were analyzed and compared with experimental data.•The Phénix control rod withdrawal tests at end-of-life were simulated.•The computational assumptions, such as the approximation of constant microscopic cross-sections in depletion calculation, were discussed. This paper introduces extended validation works on SARAX code based on the hot state data of two SFRs, the JOYO and Phénix reactors. Compared with the previous validation based on the zero-power physical tests, these validation cases challenge the code because the calculation should consider more under the operational condition, including the fuel depletion, temperature effect and geometry expansion. Besides, more computational assumptions are discussed in this paper, which contains approximation of constant microscopic cross-sections, sensitivity to different depletion chain and so on. The isothermal temperature effect and burnup reactivity swing calculation were validated using the JOYO reactor and the control rod worth were validated based on the withdrawal tests in the Phénix final tests. The results show that SARAX code has good accuracy in simulating the SFR in the hot states. The neutronic parameters such as reactivity, control rod worth, and power distribution agreed well with the experimental data.