Validation of the coupled photon transport mode in Serpent 2.2 with the Baikal-1 skyshine benchmarks

This report summarizes validation of the coupled neutron-photon transport mode in the Serpent 2.2 Monte Carlo code using the Baikal-1 skyshine benchmarks distributed with the ICSBEP. In the Baikal-1 skyshine experiment the atmospheric scattering of neutrons and photons was studied. Dose rates and flux levels above the reactor and at ground level up to 1500 m from the reactor axis were measured. The goal of the experiment was to provide a detailed study of the spatial energy dependency of atmospherically scattered particles as basis for a radiation safety analysis validation database. In addition to reference measurements, MCNP5 results are provided as part of the benchmark description.



The benchmarks were calculated using a development version of Serpent 2.2.2. Excellent agreement is observed with
the MCNP5 results in the above core neutron dose rates and reasonably agreement in the photon dose rates.
However, neutron dose rates on the two upper measurements levels are in subpar agreement with the measurement
results. Photon dose rates agree well at all the elevations. On-site detector results for fast neutron flux as well as
neutron and photon dose rates are in good agreement with the measurement and MCNP5 result across the entire
spatial range. However, on-site results for thermal neutron flux agree poorly with the reference measurements
especially at increasing distance from the reactor axis. In all cases Serpent and MCNP are in good agreement.