Evaluation of OpenMC calculations coupling with PHITS, FLUKA, and GEANT4 for ADS study

The Accelerator-Driven Subcritical system (ADS) is a subcritical reactor driven by the spallation neutrons generated in a spallation target under the bombardment of proton beam from an accelerator. To study ADS neutronics, the external spallation neutrons should be investigated carefully for coupling with a reactor core. This work focuses on the investigation into the OpenMC calculations by using different nuclear data libraries coupling with different high-energy Monte Carlo programs such as PHITS, FLUKA, and GEANT4 for ADS neutronics simulation. MCNPX direct calculations is performed as the baseline to compare to coupling-calculations. Firstly, the information of leaking neutrons from a spallation target are calculated with different codes and physical models to evaluate difference from the direct calculations to the coupling-calculations. Secondly, the neutronics characteristics of OECD-ADS model are calculated by using OpenMC calculations coupling with a surface-source from three high-energy codes to compare to MCNPX direct calculations. The neutronics parameters of mono-energy neutron for OECD-ADS evaluated from OpenMC and MCNPX with ENDF/B-VII.0 data library or only from OpenMC with different libraries are found to be in good agreement. The effect of high-energy neutrons is evaluated to be difference of around 25% in beam requirements by MCNPX direct calculations with INCL model and PHITS-OpenMC coupling-calculation with ENDF/B-VII.0 below 20 MeV. The differences in beam requirements between different coupling-calculations with the same library are compared. Moreover, the discrepancies in beam requirements from PHITS-OpenMC with JENDL-4.0/HE from 20 MeV to 200 MeV are around 15%. Finally, both neutron profiles and neutron spectra from coupling-calculations agree well with these from MCNPX direct calculations outside the coupling region of target.