Analysis of Phenix natural convection test with the TRACE code

Experimental data from the Natural Convection (NC) test performed in the Phenix reactor prior to its final shutdown have been used to further validate the single-phase sodium flow modeling in TRACE. The experimental data for the benchmark have been shared by the CEA in the frame of a Coordinated Research Project (CRP), initiated by the IAEA Technical Working Group on Fast Reactors (TWG-FR). This paper presents a complete TRACE model of the Phenix primary circuit developed for the analysis. Steady-state calculations at nominal (350 MWth) and reduced (120 MWth) power are compared to the experimental data for the validation of the model. We presents results from the 'blind' comparison, i.e. the comparison of the test results with those computed prior to the communication of the experimental data, so-called 'pre-test' results. 'Post-test' results, calculated from a model improved on the basis of the discrepancies identified from the blind comparison, are also presented. The analysis highlights the need to accurately simulate the reactor structures, since these define the thermal inertia of the system during the first phase of the transient. Furthermore, it shows the limitations of computed 1D-results when applied to the simulation of highly-stratified temperature fields. Nevertheless, the simulated reactor behavior and temperatures are found to match very well with the experimental data after the first two hours and, in general, the TRACE blind predictions may be considered as having been quite satisfactory. (authors)