There are multiple nuclear codes used to simulate the transportation of particles in a nuclear reactor, as well as multiple nuclear data libraries. One of the most popular type of code used for simulation is the Monte Carlo code. It is necessary to know if changing from a code to another, or changing the data library, has an important influence on the physical quantities such as the flux or the deposited energy. Some benchmarks have already been done, but this study is focused on the geometry of an EPR heavy reflector. In this report, three Monte Carlo codes have been compared: MCNP, TRIPOLI, and SERPENT, using nuclear data libraries such as JEFF, and ENDF/B.