Evaluation of the shielding properties of a new increased capacity storage cask for RBMK-1500 used fuel

Highlights: • Modelling of the gamma and neutron dose rates on the surface of the CONSTOR® RBMK1500/M2 cask. • Comparison of modelling results with measurements performed during the "hot tests". • Calculation results depend on flux-to-dose-rate factors that were used in the calculations. • Background radiation impacts the measurement results. • Calculated and measured doses rates are less than defined designed safety criteria for the cask. This paper presents a numerical analysis of gamma and neutron dose rates for increased capacity CONSTOR® RBMK-1500/M2 casks. Up to 202 containers of this type will be stored in the newly build used fuel dry storage facility at the Ignalina NPP site in Lithuania. The dose rate analysis comprises the application of different modelling approaches for a CONSTOR® RBMK-1500/M2 cask loaded with used fuel, which properties (irradiation time, burnup, cooling time) are known and the comparison of the modelling results with available dose rate measurements for this specific cask. The dose rate measurements that have been used for the comparison were performed during the "hot tests" of this newly built dry storage facility in 2016. During these tests, several CONSTOR® RBMK-1500/M2 casks were loaded with used nuclear fuel of different types and characteristics and transported to dedicated storage places in the storage facility. The modelling of gamma and neutron dose rates and of the source term were performed using the SCALE 6 computer codes system with detailed geometrical representation of the cask and the fuel components. The comparison of the modelling results and measurements reveals that at some points of dose rate detection are in a good agreement. Also modelling results depend on assumptions, source definitions and other parameters that are applied in the numerical modelling.