Neutron streaming experiment at FNG: results and analysis

The experimental validation of the available codes and nuclear data to calc ulate correctly the effects of streaming paths in the shield of a fusion re actor was provided by a streaming experiment carried out at the 14 MeV Fras cati Neutron Generator (FNG). The experiment consisted in the irradiation o f a mock-up of the shielding blanket (stainless steel and water equivalent material, 1 m thick) and of the toroidal field coil. A void channel with hi gh aspect ratio and a cavity at the end of the channel were realised in the bulk shield. Some nuclear quantities were measured in the cavity at the en d of the channel and behind it up to the simulated superconducting magnet. The neutron flux was measured using the activation foil technique while the nuclear heating was measured using thermoluminescent detectors. The experi mental data were compared with the results of calculations performed by the Monte Carlo code MCNP-4B, using the Fusion Evaluated Nuclear Data Library (FENDL, version 1.0, 2.0) and the European Fusion File (EFF, Versions 3.0, 3.1). The comparison shows that all the used libraries reproduce the neutro n flux generally within +/- 20% total uncertainty both in the void penetrat ion and in the bulk shield behind it. The trend to underestimate the high e nergy flux (E > 8 MeV) with increasing penetration depth is found again as in previous bulk shield experiment, showing that the relevant transport cro ss sections at around 14 MeV need further investigation. The comparison bet ween experimental and calculated nuclear heating shows an agreement within +/- 30% for all tested nuclear data libraries and in all experimental posit ions. The comparison with the case of bulk shield without penetration is al so discussed. (C) 2000 Elsevier Science B.V. All rights reserved.