• ENEA Brasimone
• generation IV
• HLM reactor
• LBE
• NACIE-UP
• wire-wrap bundle

In the context of the studies on GEN. IV/ADS nuclear systems, the correct evaluations of the temperature distribution in the fuel pin bundle is of central interest. In particular, the use of lead or lead-bismuth eutectic (LBE) as coolant for the new generation fast reactors is one of the most promising choices. Due to the high density and high conductivity of lead or LBE, a detailed analysis of the thermo-fluid dynamic behavior of the heavy liquid metal (HLM) inside the sub-channels of a fuel rod bundle is necessary in order to support the front-end engineering design (FEED) of GEN. IV/ADS prototypes and demonstrators. In this frame, the synergy between numerical analysis by CFD and data coming from large experimental facilities seems to be crucial to assess the feasibility of the components. At ENEA-Brasimone R.C., large experimental facilities exist to study HLM free, forced and mixed convection in loops and pools: e.g. NACIE-UP is a large scale LBE loop for mixed convection experiments. In the context of the SEARCH FP7 project, an experiment has to be performed in the NACIE-UP facility to assess the coolability of a 19-pin wire-wrapped electrical bundle (Fuel Pin Simulator, FPS), with heat flux up to 1 MW/m^2. The bundle is representative of the one adopted in the MYRRHA concept.
The present master thesis is devoted to the Computational Fluid Dynamic (CFD) analysis of Heavy Liquid Metal (HLM) cooled Fuel Bundles to be adopted in the Gen-IV nuclear reactors. The thesis was carried out in collaboration with the ENEA Brasimone research center, where large experimental facilities are operated to investigate HLM technology and thermal hydraulics. In particular liquid Lead or Lead-Bismuth Eutectic (LBE) is considered as working fluid.
A CFD analysis of fluid flow and heat transfer was carried out in the heavy liquid metal (LBE) cooled bundle test section of the NACIE-UP facility. The model includes the details of the wire-spacers as well as the entry region of the test section. A turbulence closure approach is adopted for all the simulations with ≈ 3.5∙10^7 nodes and a resolution of y+ = 1 - 4 at the wall in the range of interest.
A CFD code validation was carried out on experimental data by ORNL in a similar geometry cooled by sodium. Results showed a global coherence of the results and a correct description of the conjugate heat transfer effects. A good agreement was found between numerical and experimental data, although the RANS approach showed some limitations for the central sub-channel temperature distributions at high mass flow rates.
Results are compared with the up-to-date correlations on pressure loss and heat transfer and the experimental range is completely explored by CFD. The thermal structures of the test section are modelled and the role of conjugate heat transfer was assessed.
Several highlights emerged from the numerical study for the experimental campaign. In particular, the accuracy in the measurement of heat transfer between rods and fluid was evidenced as weak point of the experimental test matrix. As a consequence the test matrix was modified.
A CFD analysis of fluid flow and heat transfer was carried out in the heavy liquid metal (LBE) cooled bundle test section of the NACIE-UP facility. The model includes the details of the wire-spacers as well as the entry region of the test section. A turbulence closure approach is adopted for all the simulations with ≈ 3.5∙10^7 nodes and a resolution of y+ = 1 - 4 at the wall in the range of interest.
A CFD code validation was carried out on experimental data by ORNL in a similar geometry cooled by sodium. Results showed a global coherence of the results and a correct description of the conjugate heat transfer effects. A good agreement was found between numerical and experimental data, although the RANS approach showed some limitations for the central sub-channel temperature distributions at high mass flow rates.
Results are compared with the up-to-date correlations on pressure loss and heat transfer and the experimental range is completely explored by CFD. The thermal structures of the test section are modelled and the role of conjugate heat transfer was assessed.
Several highlights emerged from the numerical study for the experimental campaign. In particular, the accuracy in the measurement of heat transfer between rods and fluid was evidenced as weak point of the experimental test matrix. As a consequence the test matrix was modified.