Benchmarking the Three-Dimensional CAD-Based Discrete Ordinates Code "ATTILA" Using Integral Dose-Rate Experiments and Comparison to MCNP Results

The new feature of the ATTILA 3-D code to calculate dose rates in a given geometry was benchmarked using the dose rate experiments performed at the FNG 14.1 MeV source facility located at ENEA, Frascati, Italy. Two experimental campaigns were performed. Post irradiation measurements were undertaken using Geiger-Müller, TLD, and tissue-equivalent scintillators. Other measurements were also performed during irradiation. ATTILA results were compared to the experimental data and to the results of the MCNP Monte Carlo code published earlier. The calculations were performed through three consecutive steps using the same ATTILA code along with its built-in activation library, FORNAX. The ANSI/ANS6.1.1-77 and ICRP74 Ka flux-to--dose conversion factors were used. Good agreement with the experimental data and the MCNP results was obtained for times >7 d after irradiation in the 1^st campaign but large underestimation was found at shorter time steps. Both dose rates and integrated gamma fluxes are largely underestimated (∼20-40%) in the 2nd campaign.