FIFRELIN - TRIPOLI-4 coupling for Monte-Carlo simulations with a fission model. Application to shielding calculations

TRIPOLI-4 is a continuous-energy Monte Carlo transport code dedicated to shielding, reactor physics with or without depletion, criticality safety and nuclear instrumentation. FIFRELIN is a Monte Carlo code that simulates the de-excitation process of primary fission fragments leading to an estimation of prompt fission observables such as neutron/gamma/electron multiplicities and spectra in correlation with fission fragments. The TRIPOLI-4 Monte Carlo transport code and the FIFRELIN code have been coupled by means of external files so that neutron transport can take into account fission distributions (multiplicities and spectra) that are not averaged, as is the case when using evaluated nuclear data libraries. Spectral effects on responses in shielding configurations with fission sampling are then expected. In the present paper, the principle of this coupling is detailed and a comparison between TRIPOLI-4 fission distributions at the emission of fission neutrons is presented when using JEFF-3.1.1 evaluated data or FIFRELIN data generated either through a n/γ-uncoupled mode or through a n/γ-coupled mode. Finally, an application to a modified version of the ASPIS benchmark is performed and the impact of using FIFRELIN data on neutron transport is analyzed. Differences noticed on average reaction rates on the surfaces closest to the fission source are mainly due to the average prompt fission spectrum. Moreover, when working with the same average spectrum, a complementary analysis based on non-average reaction rates still shows significant differences that point out the real impact of using a fission model in neutron transport simulations