[en] In the 14 MeV neutron streaming experiment performed at the Frascati Neutron Generator (FNG) a mock-up of a module of a fusion reactor shielding system was irradiated. A void channel with a high aspect ratio (l/a>10) was penetrating through the shield and a cavity was placed at the end. Several nuclear quantities (activation reaction rates) were measured at different positions. In this work the experiment has been analysed using discrete ordinates (S_N) code DORT and the sensitivity/uncertainty code package SUSD3D. The uncertainty of the neutron flux at two measurement positions (A -- inside the cavity and B -- 87.6 cm in the shielding block) due to the iron cross-sections was found to be very low (e.g. the for the flux above 10 MeV between ∼0.2% and 3%). The uncertainty analysis is normally useful to explain the discrepancies between the calculated (C) and the measured (E) nuclear quantities, or at least to eliminate some possible sources for the discrepancy and to quantify uncertainty in design calculation. In this case the uncertainty due to the iron cross-sections seems to be too low to explain the discrepancy between C and E