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The present SF management concept in Lithuania envisages that spent RBMK-1500 fuel will be stored in dry storage containers for 50 years, before being disposed of in a deep geological repository. However, the risk that a deep geological repository will not be constructed at the planned time should be taken into account, and the extension of SF storage over 50 years should be considered. This paper presents a comparison of gamma and neutron dose rate distributions and variations with planned and extended storage times for cast iron and metal–concrete containers loaded with RBMK-1500 SF. All calculations were performed using the SCALE computer codes system. The modeling results show that the overall shielding properties of the CONSTOR® RBMK-1500 container containing the same neutron and gamma sources are better than those of the CASTOR® RBMK-1500 container. During an extended storage period (from 50 to 300 years), the total dose rate would decrease considerably and the dose rate due to neutrons would become dominant for both containers. [ABSTRACT FROM AUTHOR]

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. • 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. [ABSTRACT FROM AUTHOR]