**Author details**

*Recent Advances in Numerical Simulations*

against either available or expected experimental data.

the calculation of inlet-plenum flow distribution.

ANL Argonne National Laboratory CEFR China Experimental Fast Reactor CFD Computational Fluid Dynamics CIAE China Institute of Atomic Energy CRP IAEA Coordinated Research Project

EBR-II Experimental Breeder Reactor II FFTBM Fast Fourier Transform Based Method

DOE (US) Department of Energy DHX Dump Heat Exchanger

The NINE's Simulation Models have been developed strictly complying with the Best Estimate principle - which namely requires avoiding the introduction of inaccuracies due to rough approximations and assumptions - thus trying to represent at best the problem under investigation without adopting any major simplification. Despite this approach requires relevant and continuous computational efforts, the obtained results show-up highly satisfactory and encouraging in a whole. Moreover, as far as the computation capacity is concerned, the NEMM model methodology developed by NINE confirmed its applicability also in the case of SFR simulations. The present chapter summarizes the activity carried-out, presents the results and discusses the main outcomes of the mentioned benchmark exercises, underlying the wide convergence among the computational tools, as well as detecting the main discrepancies and seeking for their common origin and trends, which should enable defining a mid-term vision for further development of the computer codes in the field of fast reactors and identifying new needs for their extended validation

Among others, the following items have been identified as meriting careful and particular attention in the future: the need for an accurate modelling of the mixing of coolant flows in the assembly, the estimation of the pressure drop and the flow distribution during the transients which could be significantly improved using suitable empiric correlations, the sodium mixing and the thermal stratification phenomena which play a crucial role during the transients, and are sensitive to the nodalization scheme adopted and cannot be accurately predicted by the current existing SYS-TH codes, the need for a correct and comprehensive simulation of the heat transfer between adjacent subassemblies, the suitability for improvement of

Moreover, the importance of the representativeness, exhaustiveness and comprehensiveness of data have been once more and even farther pointed-out, claiming the need for complementing and/or implementing the existing data base with the results of experimental programs, engineered to match some specific validation needs, thus addressing, and filling the main and more crucial knowledge gaps. Definition of such programs should rely upon accurate to avoid duplication and

The data and information presented in this chapter are part of two ongoing IAEA coordinated research project; the first one on "Benchmark Analysis of Fast Flux Test Facility (FFTF) Loss of Flow Without Scram Test – CRP-I32011", and the second one on "Neutronics Benchmark of CEFR Start-Up Tests – CRP-I31032".

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dispersions.

**Glossary**

**Acknowledgements**

Domenico De Luca1 \*, Simone Di Pasquale1 , Marco Cherubini1 , Alessandro Petruzzi1 and Gianni Bruna1,2

1 Nuclear and Industrial Engineering (NINE), Lucca, Italy

2 NucAdvisor, Courbevoie, France

\*Address all correspondence to: d.deluca@nineeng.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
