Heavy Liquid Metal Cooled Reactors (HLMCRs) are among the most promising Generation IV concepts. In view of the growing interest towards these systems, HLMCR core design activities are currently being pursued worldwide. The core design of a fission reactor is a complex task that must take into account the intrinsically multi-physics nature of the system. Computational tools that are reliable while being fast running are required both in support of the core design phase and to assess the reactor behaviour during operational and off-normal transients. The specific features of HLMCRs, namely the fast neutron spectrum and the liquid metal coolant, determine a different behaviour with respect to commercial light water reactors, thus calling for the development of specific codes.