This paper shows models developed and results obtained for neutronics simulations of the 3D core of C5G7-TD Benchmark using the Serpent code, and an approach for multi-physics coupling for Serpent/CTF codes was presented. Neutronic simulations included control rod movements and moderator density changes, showing good Serpent results when compared to other codes. Future efforts will include the multi-physics simulation of the transients included in Phase II of the Benchmark.