With the progress and the born of new economies with a willingness of fast growth, the global demand of energy has increased constantly. For these reasons, the world is currently experiencing an increasing need for development of sustainable, low-carbon energy sources as a core of the future energy supply. One of such sources is nuclear power. Starting to be a well-affirmed energy source, also nuclear power has to face innovation. In this scenario plays a key roe the Generation IV International Forum (GIF) initiative has identified six main designs that will constitute Generation IV reactors. One of these designs is Gas-Cooled Fast Reactors (GFR), of which ALLEGRO reactor should be the first prototype.