This master thesis is about an improvement of a dynamic model of a supercritical CO2 loop for fusion nuclear applications. This improvement is divided in three subprojects: a molten salts cycle, a pressure control system and the coupling of the last two. Moreover, it was necessary to change the initial model in order to improve its performance and make it easier to use, these changes go from a visual change of the base case, to a new medium library, passing throw a change in PI controllers. This entire model is modelled using Modelica with a Dymola environment. Dymola is a complete environment for model creation, testing, simulation and post-processing. Inside the project all the issues related with the installation and setting up of this software are explained as also the libraries used from open source Modelica: ThermoPower, SolarTherm and ExternalMedia. Finally, when the new features have been implemented to the model, they have been compared with the base case in aspects as components’ power, efficiency, thermodynamic diagrams and key variables