Benchmark of System Thermal-Hydraulic Codes for the Test Section of the Dip Cooler Instability Test Facility

The Dip Cooler Instability (DCI) Test Facility is designed to investigate the thermal-hydraulic behavior of two parallel bayonet tubes, and aims at supporting the characterization of the dip cooler Decay Heat Removal (DHR) system employed in newcleo's 30 MWe Amphora-Shaped Lead-cooled Fast Reactor (LFR-AS-30). Within the framework of newcleo's Verification and Validation (V&V) roadmap, this study presents a code-to-code benchmark based on the pre-test model developed with the system thermal-hydraulic codes AC2-ATHLET 3.4.1 and RELAP/SCDAPSIM/MOD4.1. Focusing on a subset of cases in the experimental test matrix, the numerical results are compared to assess the level of agreement between the codes. The comparison highlights significant differences mainly stemming from the determination of the heat transfer mode and from the interphase mass transfer model. Then, the comparison with the experiments reveals discrepancies caused by the deviation of the measured wall temperature from the setpoint, as well as by a possible underestimation of the effective thermal conductivity of the helium gap in the numerical models. This consideration is corroborated by a preliminary uncertainty quantification analysis performed with the ATHLET code. Future activities will focus on the post-test analyses performed with a more detailed model of the DCI Test Facility.