The overall objective of the NURESIM Multi-Physics subproject (NURESIM-MP) activities is to integrate the simulation tools developed within the NURESIM Core Physics subproject (NURESIM-CP), with the simulation tools developed within the NURESIM Thermal-Hydraulics subproject (NURESIM-TH), to complete the European software platform and enable coupled neutron-kinetics/thermal-hydraulics transient simulations of operational and design basis accident conditions for existing LWR's (PWR, BWR, VVER). The first NURESIM-MP developments are described and the first, proof-of-principle, applications to multi-physics and multi-scale problems using the European codes CRONOS2, FLICA4 and COBAYA3 are presented and discussed. Thus, a coupled N/TH application using the CEA codes CRONOS2 and FLICA4 was developed using the advanced multi-physics functionalities of the SALOME software, on which the architecture of the European platform will be based. The coupling application includes a mesh-to-mesh interpolation tool that was developed in order to allow coupling N and TH solvers using non identical three-dimensional meshing schemes. A generic Application Programming Interface was also developed to allow for a flexible manipulation and coupling of different solvers, which is a prerequisite for the development of complex multi-physics calculation routes. The first exercise applies a N/TH coupling of CRONOS2 and FLICA4 inside the SALOME-based platform for the analysis of a test case derived from the NEA-OECD PWR MSLB Benchmark. The second exercise applies the COBAYA3 core 3D fine-mesh multi-group neutron diffusion solver using a domain decomposition method, which allows for an efficient parallel implementation in memory distributed multi-processors.