[en] Full text: There is only one nuclear power plant in Lithuania - the Ignalina NPP (INPP). The INPP possesses two similar units of RBMK-1500 reactors. The INPP reactors were commissioned in December 1983 and August 1987 respectively. In 1992 decision was made to build an interim dry spent nuclear fuel storage facility at the INPP site. In the early November 1992 tender invitations were extended to nine companies, and finally, the proposal of the German company GNB was accepted to store the spent nuclear fuel outdoors in sealed metal CASTOR RBMK-1500 casks filled with helium. May 12, 1999 the first cask was loaded with the SNF and transported to the storage site. According to the licensing requirements the testing programme for five casks was performed, the report was prepared by operator and approved by VATESI. The license for the operation of the storage facility (from 15 February, 2000) was issued by VATESI February 11, 2000. The licence is issued for 5 years. In total twenty of such cast iron CASTOR RBMK-1500 casks were already loaded with SNF. Agreement for the delivery of 40 metal-concrete CONSTOR RBMK-1500 casks instead of CASTOR RBMK-1500 casks was signed with GNB. Now already about 20 of such casks are loaded with the SNF and delivered to the interim storage facility. The storage site for the 72 casks is the open type facility. To decrease the dose to the public and personal the concrete wall around the casks was built. The CASTOR RBMK-1500 and CONSTOR RBMK-1500 casks are designed for the long-term (up to 50 years) storage of 102 RBMK half-fuel assemblies, which are positioned in the special basket. The CASTOR RBMK-1500 cask body is made of ductile cast iron. The cask has two lids made of corrosion protected carbon steel. The first lid is provided with a double-barrier sealing system to secure leak tightness. The second lid (guard lid) minimises radiation exposures and ensures the weather and additional corrosion protection of the containment barriers. The body of CONSTOR RBMK-1500 is made of two welded metal cylinders. The space between them is filled with reinforced heavy concrete. The cask has three lids. The first one if fixed to the upper ring and there is a seal there. Two other lids are welded to the body of the cask. In this paper results on comparison of the main characteristics, such as maximum cladding and surface temperature, dose rate at the surface and at the some distance, and also criticality, for CASTOR and CONSTOR casks loaded with RBMK-1500 spent fuel is presented. Comparison was performed when the cask is just loaded with spent nuclear fuel, and after 50 years of storage (possibly going for disposal) for the same RBMK-1500 SNF: initial enrichment of the fuel - 2 %, burn-up - 20 GWd/MTU, cooling time - 5 years, and the same weather conditions. It was revealed that maximum cladding temperature is higher for CONSTOR RBMK-1500 cask but surface temperatures are similar for both casks. After 50 year storage in wintertime surface temperature can reach values bellow zero. Analysis of radiation characteristics showed that CONSTOR RBMK-1500 cask has better shielding characteristics than CASTOR RBMK-1500 cask. During 50 years of interim storage period the total dose rate is decreasing from 5 to 20 times in dependence on the location of the point detector and type of the cask. Criticality analysis of CASTOR RBMK-1500 and CONSTOR RBMK-1500 casks demonstrated the effects of the geometrical configuration of fissile material and its distance to the wall of the cask on the value of the effective neutron multiplication factor k_eff for different density of the water. They also demonstrated that effective neutron multiplication factor k_eff for an unfavorable operational and hypothetical accident condition is less then allowable value 0.95. (author)