Verification and Validation of Depletion Calculations for TRISO Fuel Against Data from the Second Advanced Gas Reactor Irradiation Campaign

Verification and validation of the Monte Carlo particle transport code Serpent 2 depletion calculation capabilities in the context of tristructural isotropic (TRISO) particles was performed against available data from the second Advanced Gas Reactor irradiation campaign (AGR-2), which was irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory. The AGR-2 test train contained both uranium oxycarbide (UCO) and uranium dioxide (UO₂) TRISO particles, which were irradiated for 12 ATR power cycles over a period of 3.5 years. For this study, the AGR-2 test train was reconstructed in full detail using Serpent 2, and depletion calculations replicating the experimental irradiation conditions were performed. The fast neutron fluence and AGR-2 fuel burnup resulting from the depletion calculations for the 12 irradiation cycles are compared with the corresponding reported MCNP-computed data. The total AGR-2 fuel burnup accumulated by the end of the AGR-2 test train irradiation is also compared with available experimental data. The fission product inventory at the end of the AGR-2 irradiation obtained from the Serpent 2 depletion calculations is compared with the reported computational data. The Serpent 2 results for the fast neutron fluence (E_n > 0.18 MeV) differ on average by 5.10% from the MCNP-computed results. Similarly, the Serpent 2 model underpredicts the AGR-2 fuel burnup at the end of the irradiation by 5.13%, on average for all capsules, when compared with the MCNP-computed results and by 2.01% when compared with the experimental results. Last, the fission product inventory calculated by Serpent 2 is underpredicted by 5.27%, on average for all capsules, in comparison with the reference MCNP data. Serpent 2 is generally in satisfactory agreement with the AGR-2 reported values. These results provide confidence in the performance of Serpent 2 depletion calculations for TRISO fuel particles.