Protected loss of flow accident simulation in circe-hero facility: experimental test and system code assessment

In the framework of the Generation IV ALFRED (Advanced Lead Fast Reactor European Demonstrator) design, a dedicated Test Section (TS) named HERO (Heavy liquid mEtal pRessurized water cOoled tubes) has been implemented in the large LBE (Lead-Bismuth Eutectic) pool integral effect CIRCE (CIRColazione Eutettico) facility at CR ENEA Brasimone. HERO is a mock-up (1:1 in length) of the ALFRED Steam Generator (SG), consisting of seven double wall bayonet tubes arranged in triangular pitch inside a hexagonal shell, with an active length of ~6 m. An integral test experiment has been designed and carried out in the framework of the HORIZON2020 SESAME (Simulations and Experiments for the Safety Assessment of MEtal cooled reactors) European project. The test consists in a Protected Loss of Flow Accident (PLOFA) occurring with the facility operated in nominal steady-state conditions for both primary side (LBE) and secondary side (high pressure water). In steady-state conditions, the LBE mass flow rate is promoted by the injection of argon simulating the behavior of the primary pump, while the thermal power is supplied with an electrically heated Fuel Pin Simulator (FPS). The transient is obtained reducing the FPS power according to a characteristic heat decay curve, while the loss of the primary pump is simulated by the reduction of the gas injection. The loss of the heat sink is simulated managing the HERO feedwater in the secondary loop. A simulation activity has been carried out with RELAP5-3D© v. 4.3.4 system thermal-hydraulic code. A numerical model of the primary loop and HERO SG have been set up and employed to reproduce the main phenomena involved in the system during the test. The present paper aims to present and to describe the experimental results achieved during the transient and to compare the code results with the experimental data.