Pre-test analysis of accidental transients for ALFRED SGBT mock-up characterization

In the framework of the Horizon 2020 SESAME project (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors), the CIRCE pool facility has been refurbished by ENEA to host HERO test section (Heavy liquid mEtal pRessurized water cOoled tubes) with the aim to test an innovative concept of the steam generator bayonet tubes proposed for ALFRED (Advanced Lead Fast Reactor European Demonstrator) and to provide experimental data for code validation. HERO consists of a bundle of seven bayonet tubes characterized by an active length of six meters (1:1 with the ALFRED steam generator tube length). The main purposes of the research were to investigate the thermal hydraulic behavior of the innovative concept and provide a set of experimental data aiming at validating STH (System Thermal-Hydraulic) code. The calculations were carried out adopting RELAP5-3D©, updating the nodalization scheme validated with the experimental data of CIRCE-ICE campaign. The experiment consists of a transition from forced to natural circulation in a loss of flow accidental scenario; in order to identify the initial conditions of the experiment, several full power conditions were simulated. Starting from the reference steady state conditions, five transient tests were simulated to evaluate the effect of the reduction of the secondary mass flow rate (reduced from the nominal value to simulate the activation of the DHR system) and the effect of the heat losses compensation. According with the calculation, HERO test section offers excellent thermal-hydraulic behavior ensuring a sufficient natural circulation conditions to remove the decay heat in the short term