[en] The study of thermal-hydraulic performance of a fixed bed nuclear reactor (FBNR) core and the effect of the porosity was studied by the CFD method with 'SolidWorks' software. The representative sections of three different packed beds arrangements were analyzed: face-centered cubic (FCC), body-centered cubic (BCC), and a pseudo-random, with values of porosity of 0.28, 0.33 and 0.53 respectively. The minimum coolant flow required to avoid the phase change for each one of the configurations was determined. The results show that the heat transfer rate increases when the porosity value decreases, and consequently the minimum coolant flow in each configuration. The results of minimum coolant flow were: 728.51 kg/s for the FCC structure, 372.72 kg/s for the BCC, and 304.96 kg/s for the pseudo-random. Meanwhile, the heat transfer coefficients in each packed bed were 6480 W/m"2*K, 3718 W/m"2*K and 3042 W/m"2*K respectively. Finally the pressure drop was calculated, and the results were 0.588 MPa for FCC configuration, 0.033 MPa for BCC and 0.017 MPa for the pseudo-random one. This means that with a higher porosity, the fluid can circulate easier because there are fewer obstacles to cross, so there are fewer energy losses. (authors)

[en] The European Nuclear Young Generation Forum (ENYGF) is the event organised every 2 years within the European Nuclear Society - Young Generation Network (ENS-YGN) for European young professionals and students. It consists in 3 days of conferences (plenary sessions, workshops, panel sessions, technical and poster session), 1 day of technical tours and 1 day of cultural visits. ENYGF 2015 is dedicated to the dual aspect of the relationship between nuclear power and environment: the impact of nuclear activities on the environment and the contribution of nuclear energy to fight climate change. A great deal of this document is composed of the slides of the presentations