Solving partial differential equation numerically is nowadays a standard technique to study real problem application, both in industrial or research activities, where complex physics and/or geometry are involved. A lot of validated numerical discretization methods (Finite Elements,Finite Volumes, etc..) are available, along with dedicated softwares. Anyway, in most cases the problems analysed are actually very expensive by a computational point of view, that usually translates in very long time to get the solution. One perfect example of difficult resolution for strandard discretization methods is represented by the multiphyscs of Molten Salt Fast Reactors. One possible way to reduce computational costs are Reduced Order Modelling techniques.