The Molten Salt Reactor Experiment (MSRE) was a circulating fuel thermal reactor built and operated in the sixties. As the only Molten Salt Reactor (MSR) testing facility for which extensive experimental data are available, it can be considered as a reference for the development of modeling approaches for the studies related to the Gen-IV MSR. In this work, a geometric multi-scale approach has been adopted for the simulation of the MSRE plant. The data and the experimental results relative to the U-233 fuelled reactor are considered. The neutronic parameters have been determined using the Monte Carlo code Serpent. The reactor core is divided into three radial regions, each one described by a 3D channel in which Navier-Stokes and energy conservation equations plus delayed neutron precursors (DNP) balance equations are solved. Determination of the generated power is obtained employing a point kinetics like equation, fed with importance weighted values of temperatures and DNP concentrations. The remaining part of the plant, that includes the primary and secondary cooling circuits, is modeled by means of zero-dimensional components. The results attained with such modeling approach are compared with experimental data both in time and frequency domain, showing good agreement. The adopted approach, thanks to the punctual, coupled solution of the governing equations in the core, gives better insights into the thermal behavior of the graphite and its effects on MSR dynamics than commonly used correlation-based solvers.