[en] Full text: At Paks NPP, Hungary, the C30 cask mainly used for the transport of the assemblies from the at-reactor wet service pool to the storage facility, so it primarily serves as an interface to the storage place. Occasionally, it is used for transport from a unit to an other one. Originally, the C30 cask was licensed to the following parameters: Max. number of assemblies 30; Total heat production < 15 kW; Average burnup of the cask load < 33 GWd/tU; Burnup of a single assembly < 40 GWd/tU; Initial enrichment < 3.7 %; Cooling time > 2.5 years. Due to the introduction of the new fuel assemblies, the higher burnup achieved by the old type fuel assemblies and to the need of the lower cooling time the NPP applied for the modification of the license which allow the extension of the parameter range described above. This study examine of the impact of this extension on the subcriticality, on the radiation shielding and on the radiolysis (hydrogen production in the water by the absorption of gamma radiation). The desired range of the parameters extends to 50 GWd/tU burnup of a single assembly and 0.5 years of cooling time for three type of fuel. These types of fuel the old type fuel assemblies (no enrichment zoning, max. enrichment is 3.6 %), the new Russian designed assemblies with enrichment zoning (average enrichment is 3.82 %) and the BNFL designed fuel with enrichment zoning and with gadolinium (average enrichment is 3.9 %) are examined. The main findings of this study can be summarized as follows. The subcriticality requirements are met by the C30 cask loaded with fuel assemblies listed above for normal and accidental condition as well with fresh fuel assumption. The results of the thermohydraulical analysis were utilized in the analysis. Based on the constraints from the heat physical analysis, we examined the influence of the extended parameters on the neutron and photon dose rates. The maximum acceptable number of loaded assemblies with extended parameters was investigated. Loading strategies are suggested for different values of burnup and cooling time to meet the radiation protection safety requirements. The hydrogen production from the water by gamma radiation was examined. The time limit for the explosion hydrogen concentration was determined by a high degree of conservatism. Proposals were made for the case of inadvertent conditions to avoid achieving this concentration. (author)