Thermal-hydraulic post-test analysis of the transition from forced to natural circulation in ICE test section

This report, carried out at the DIMNP of the University of Pisa, in collaboration with ENEA Brasimone Research Centre, illustrates the thermo-fluidynamic results of the analysis, performed by the RELAP5 system code, of an experimental test recently carried out at ENEA on CIRCE facility. In particular, the so-called Test D of the last experimental campaign performed with the ICE test section was considered. This test simulates an Unprotected Loss Of Flow (ULOF) accident transient of interest far the safety of HLM reactors. The aim of this test was to investigate the transition from forced to natural circulation in the primary system. The RELAP5/Mod3.3 code, modified in order to take into account the LBE fluid properties, was employed to reproduce the phenomena occurring during the test transient and to assess the capability and limits of the code by comparing the numerical results with experimental data.