Post-Test Analysis of SIRIO Facility Data by System Thermal-Hydraulic Codes for LFR Application

As part of the R&D activities supporting Generation IV innovative nuclear technologies, an experimental facility named SIRIO has been designed and constructed to test and validate a new concept of Decay Heat Removal system at a relevant scale for Gen-IV Lead-cooled Fast Reactor (LFR), in particular for the DEMO LFR ALFRED. This innovative system provides a safe long-term cooling condition of the reactor coolant system with no need of external action or energy supply, and claims capability to passively control the heat removed by the ultimate heat sink thanks to non-condensable gases. This new concept is attractive for LFRs because it can prevent the early freezing of lead, which is a concern after the proper intervention of the DHRs. In addition, for water cooled reactors, passive control of heat transfer capability reduces the thermal stresses on the materials, smoothing the fluid internal thermal gradients and the depressurization rate. In this work, SIRIO facility is described, along with the numerical model developed using the RELAP5/Mod3.3 thermal-hydraulic system code. Part of the efforts in the experimental campaign within the EU project PIACE aims at reproducing the conditions of ALFRED in Stage 2 configuration (i.e., loop and gas pressure set at 180 and 110 bar, respectively). The experimental outcomes are compared with those obtained with RELAP5 code to validate the numerical tool for LFRs applications and to assess the code capability in reproducing two-phase natural circulation conditions with noncondensable gases and the system response during accidental scenarios.