Validation of the modified ATHLET code with the natural convection test of the PHENIX reactor

• Modification of system code ATHLET for Sodium-cooled Fast Reactors application.
• Development of a properties package as well as a heat transfer package for sodium.
• Validation of the modified code with the PHENIX reactor ultimate natural convection test.

This paper presents the modification, validation and application of the system code ATHLET for Sodium-cooled Fast Reactors. The ATHLET code is developed by Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) in Germany for Light Water Reactors application. The code structure is modified that it can be easily extended to different fluids. For the present analysis of SFR, a sodium property package as well as heat transfer correlations for sodium are implemented into the code. To evaluate the feasibility of the modified code, the PHENIX reactor, a SFR operated by French Alternative Energies and Atomic Energy Commission (CEA) from 1973 to 2009, is modeled. Two different modeling approaches of the hot and cold plenum of the PHENIX reactor are adopted, i.e. the one-dimensional representation with standard pipes, and the pseudo-three-dimensional representation with parallel channels connected via cross connections. Both models are used for simulation of the natural convection ultimate test scenario of the PHENIX reactor, and the results are compared with the measured data. Improvement approach for the pseudo-three-dimensional modeling method is proposed and realized. The results reveal advantage as well as limitation of the current models, and good applicability of the modified ATHLET code to sodium-cooled reactor systems.