[en] The thermal analysis was performed on two types German made CASTOR RBMK-1500 and CONSTOR RBMK-1500 casks for interim storage of spent fuel at Ignalina NPP. Numerical calculation code ALGOR (USA) was used. The calculations were performed for different cases of single cask or cask in storage when it is just loaded with spent fuel and after 50 years of storage, for summer and winter conditions. It was established that in all cases the maximum temperature of fuel cladding never exceed the maximum allowable temperature. It was obtained that from the thermal point of view the casks can be used for the interim storage of spent fuel pre-stored for at least 5 years in water pools. (author)