Validation of Serpent 2 depletion calculations against experimental data from the Advanced Gas Reactor (AGR) irradiation campaign

This paper presents the first steps of the validation process for accurate multi-physics TRISO (Tri-structural isotropic) fuel performance models. These models can determine the fuel operational conditions for advanced pebble bed Fluoride-cooled and Gas-cooled, High-temperature reactor concepts. Specifically, an effort is being carried to validate the Monte Carlo particle transport code Serpent 2 using the experiments of the Advanced Gas Reactor (AGR) program which have been irradiated in the Advanced Test Reactor (ATR) at the Idaho National Laboratory (INL). For this project, detailed specifications were compiled for the AGR-2 experiment and a corresponding model was created using Serpent 2. AGR-2 contains both UCO and UO₂ TRISO fuel which was irradiated for 12 ATR power cycles. At this stage, the calculations were performed twice, first assuming a fresh ATR core, specific constant outer shim control cylinders (OSCC) locations and imposed power and second assuming a slightly depleted fresh fuel for ATR and using the ATR operational conditions of the AGR-2 irradiation cycles. The results of the detailed physics depletion calculations developed for the AGR-2 are compared to the MCNP simulations performed prior to the irradiation and the measured experimental data provided from INL respectively. Fast flux (E > 0.18 MeV) for the 147A cycle varied from 4.31 to 6.92 [10¹³ n/cm²/s] (E > 0.18 MeV) which differs from the experimentally measured values by 1.47% up to 12.19%. The Serpent 2 data are generally in good agreement with the AGR-2 reported values. (authors)