[en] Recently the problem of the spent fuel treatment is very important because of the limited space for the waste storage in the NPP 'Kozloduy'. Now on the site 4008 casks from WWER-440 and 617 casks from WWER-100 reactors are stored. Assessments show a total amount of 9940 casks from WWER-440 and 3325 casks from WWER-1000 by the end of the reactors operation period, containing 204330413 kg Uranium. The results of the analyses show that after the reloading in 2001 the all on-site waste storage facilities will be full. A technical-economical comparison has been made among the e 4th methods: on-site long-term storage; transportation and processing in Russia; transportation and processing in Great Britain; transportation and processing in France. International experience show a trend of postponement of the spent fuel processing and the long-term storage. Dry storage with a passive cooling is recommended. The result of the economical comparison among the three possible variants for dry storage (casks, horizontal concrete modules, vault) show that 3th variant (vault) is most appropriate because of minimal specific cost of 25.02/kgU. This type of storage suites all safety standards and shows a number of technical advantages compared to the other methods