Comparison of System Thermal Hydraulic and CFD Analyses of NACIE-UP Asymmetric Test

Abstract

Liquid Metal Fast Reactors (LMFRs) are expected to play an important role in the future of nuclear energy as they offer higher fuel efficiency, high power density and excellent safety characteristics due to the optimal heat transfer performance of the metallic coolants.

The NACIE-UP loop facility, installed at ENEA Brasimone R.C. in Italy, is specifically designed to perform experimental campaigns for natural circulation testing; in particular to investigate the shift from forced to natural circulation in a test section with lead-bismuth eutectic (LBE). In 2017, ENEA conducted transient tests which provided an excellent opportunity to validate both integral values and local temperature distribution, allowing code validation by comparisons of reactor system codes and CFD simulations with experimental data.

In the framework of a benchmark organised by an IAEA Coordinated Research Project, NRG will perform multi-scale simulations of asymmetric transient tests by coupling the NRG’s system code SPECTRA to a commercial CFD code. To this end, this paper presents the comparison results obtained by SPECTRA and CFD for two steady-state conditions, ADP10 and ADP06. Both codes demonstrate reasonably good agreement in predicting the wall and bulk temperatures of the fuel pin simulator (FPS). The CFD model can predict the detailed temperature variations across three measurement planes in the FPS, especially evident in the non-uniform power distribution test, ADP06. The 3D effects introduced by the wires can be addressed accurately in the CFD regarding the pressure drop in the FPS. Comparative analyses between numerical and experimental results demonstrated a good agreement, providing positive feedback on the feasibility of coupled simulation to enable a smooth and stable coupling.