Developing a Full-Core MCNP6 and RELAP5 Model of the European Pressurized Reactor Using NWURCS

The European pressurized reactor (EPR) is classified as a Generation III+ reactor. It differs from a conventional pressurized water reactor in many aspects, one of which is the core design. This evolutionary reactor lends itself to new fuel designs, such as thorium-based fuels. To perform new design calculations, a base case model needs to be established because the detailed models that are currently available are either proprietary or regulated. This paper therefore presents such a model based on the Monte Carlo method. This method is a valuable component of reactor neutronic calculations because geometry and materials can be accurately modeled.

We modeled a full core of the EPR using MCNP6, in which the individual fuel pin geometry and material definitions were used together with radial and axial temperature characterization based on fuel assemblies considered as nodes. Data for both the neutronic and thermal-hydraulic models were mainly obtained from the U.S. EPR Final Safety Analysis Report (FSAR) [Rev. 5, AREVA (2013)].

The neutronic and some thermal-hydraulic results were compared with data from the EPR FSAR. The following core neutronic parameters compared well with the FSAR data: the boron worth, axial flux distribution, neutron flux spectrum, reactivity coefficients, and control rod worth. However, the delayed neutron fraction showed a somewhat larger difference compared to the FSAR. Given this verification with the FSAR, confidence in the MCNP6 EPR model was therefore established. The model that we have developed serves as the basis for the follow-on study of introducing thorium in the EPR core.