In the last years, new interest in nuclear space propulsion has been shown by space agencies. NASA defines Nuclear Thermal Propulsion (NTP) as a key technology for long-range spaceflight. Many HEU (Highly Enriched Uranium), fast reactors design for space applications were proposed during and after NERVA and ROVER projects. HEU reactors have many advantages: they are usually more compact than LEU (Lowly Enriched Uranium) reactors, they show a longer operating lifetime and safety in accidental scenarios can be easily ensured. Their main drawback is the high content of fissile materials, which is a primary security concern. The present work investigates the possibility of a LEU reactor design with CERMET (Ceramic Metallic) fuel and its optimization.