Implementation of Lead-Lithium as working fluid in RELAP5/Mod3.3

University of Pisa (UniPi) has been involved for years in the implementation of a dedicated version of RELAP5 STH code capable to simulate liquid metals cooled systems. The main Verification and Validation (V&V) activities were focused on Gen-IV fission reactors employing Lead and Lead Bismuth Eutectic (LBE) as coolants. This specific modelling background has brought UniPi to expand the code domain of application to Lead-Lithium Eutectic (LLE) given its extended application as breeding medium in future fusion reactors. The paper illustrates the implementation procedures of the thermo-physical properties of Lead-Lithium as working fluid in RELAP5/Mod.3.3. The last revised LLE properties were assigned to the code by inserting the transport properties (thermal conductivity, dynamic viscosity, and surface tension) directly in the FORTRAN source file, while the thermodynamic properties (density, isobaric specific heat, internal energy, etc.) were implemented in tabular form as an external file. Furthermore, the code capabilities to reproduce Lead-Lithium behavior were assessed for a reference configuration case. The numerical outcomes were compared with an analytical solution (epsilon-NTUmethod), providing a first fundamental step in the validation process towards more complex models simulating Lead-Lithium systems of interest for fusion reactor applications.