State-of-the-art review of the T/H system codes RELAP5 for HLM applications

Thermal-hydraulic code RELAP5, originally developed by INEEL under NRC contract for LWRs LOCA analysis, has been extensively validated and it is actually used worldwide as a best estimate code for LWRs transient analysis. This code was chosen in the early 2000s as the reference code for the thermal-hydraulics and accident analysis of Heavy Liquid Metal Fast Reactors within the frame of Italian research programs. Several original RELAP5 routines have been updated in order to implement suitable correlations generating the reference physical and thermodynamic properties for Lead and Lead-Bismuth Eutectic fluids. Similarly, some specific heat transfer correlations for liquid metals have been added. In almost twenty years, ENEA has conducted an extensive validation program to demonstrate the capability of the code to simulate the thermal-hydraulic behaviour of heavy liquid metal systems. This program was mainly conducted on the facilities of the Brasimone center (CHEOPE, CIRCE, NACIE), but also used data from international programs (MEGAPIE International Experiment and LACANES Benchmark OECD/ NEA). Furthermore, the participation of ENEA in the projects financed by the European Commission in several Euratom programs for the study and design of HLMcooled reactors (ELSY, SEARCH, MAXSIMA, LEADER, SESAME. MYRTE) has allowed to increase the confidence on the transient and accidental analyses conducted with RELAP5 also through the comparison with the results of other codes. RELAP5 is currently a reliable tool both as a support to reactor design (safety by design) and for accidental analyses.