Fuel rodlet power determination during the qualification experiment of the ISABELLE-1 power ramp test device of OSIRIS reactor using 3D NEPTUNE_CFD/SYRTHES simulations

In this work, an engineering study based on a NEPTUNE/SYRTHES coupled-code methodology is proposed to calculate the maximum linear heat rate (MLHR) of the fuel rodlet during the ETALISA-1 qualification experiment of the ISABELLE-1 Power Ramp Test Device (PRTD), operating at the Osiris reactor. The rodlet MLHR is determined from the thermal balance (TB) of the device's water loop, and the results are compared with the reference values used for the qualification of at the time: the TB calculated with REFLET code and the Nb-isotopic analysis measured during Post-Irradiation Examinations (PIEs). The methodology aims to support design optimization and improve the accuracy of power determination for ADELINE, the future PRTD of the Jules Horowitz Reactor. The two devices share indeed several key characteristics, including design, operating principles, and irradiation conditions. Therefore, validating the methodology on ISABELLE-1 is expected to provide valuable insights on the TB of ADELINE and in the power rodlet determination accuracy. The method proposed is based on the coupling of Computational Fluid Dynamics (CFD) and solid thermal transient simulations, respectively simulated using NEPTUNE_CFD 9.0 and SYRTHES 5.0 codes. The simulation strategy is developed to study the ETALISA-1 experimental conditions. The coupled-method results for rodlet power predictions showed good agreement with the PIE and REFLET results, within a 1σ uncertainty range. Additionally, the CFD approach provided insights into water behaviour within the device, enabling direct comparisons with some REFLET's past correction factors related to water dynamics without requiring additional predictive models or tools. Therefore, the study establishes a robust framework for its future applications on ADELINE. • Thermal-hydraulics and thermo-mechanical modelling of the ISABELLE-1 power ramp test device. • Development of coupled NEPTUNE_CFD and SYRTHES method for fuel irradiation studies in research reactors. • Model validation through ETALISA-1 experiment performed in the Osiris research reactor.