Generation of particle self-shielded neutron cross-sections for the Monte-Carlo code TRIPOLI-4

Self-shielding effects of micrometric particles randomly distributed in nuclear materials were the subject of extensive studies. These effects are known as a double-heterogeneity problem due to “microscopic” heterogeneities, involving the decrease of the neutron flux inside the particles, and “macroscopic” heterogeneities, affecting the neutron flux distribution over the entire volume containing those particles. The present study aims to take advantage of the capabilities of the GELINA facility (JRC-Geel, Belgium) in terms of non-destructive analysis of materials to validate experimentally any models developed to solve the double heterogeneity problem. In order to complement past experiments carried out at the GELINA facility, new transmission experiments were carried out on long cylindrical samples containing microspheres of Gd2O3 with diameters of 195 and 380 μm dispersed in UO2 pellets. The analysis of the experimental transmission spectra with the resonance shape analysis code REFIT and Monte-Carlo neutron transport code TRIPOLI-4® demonstrates that the particle self-shielding model proposed by Doub can reproduce the huge attenuation of the neutron absorption in the Gd resonances by reducing significantly the computational cost of Monte-Carlo simulations.