The basic rationale behind the RBMK was the desire of the Soviet government to produce large nuclear power plants as inexpensively as possible. The RBMK met this goal well, but sacrificed safety in order to do so. One of the main attractions of the RBMK was that it was built out of modular components that could be produced by existing Soviet industry. At the time the first RBMK-1000 was being built at Leningrad in the late 1960s, the Soviet Union had extreme difficulty manufacturing the forgings needed for large pressurized water reactors. The RBMK could also operate using low-enriched uranium oxide fuel- 2.0-2.4% U-235. This served as another cost-saving measure. The 2.0% fuel generally has a burnup of around 30,000 Megawatt-days per metric ton of heavy metal.
So what becomes of spent RBMK fuel? According to End Points for Spent Nuclear Fuel and High-Level Radioactive Waste in Russia and the United States (2003):
Also see this article from the antinuclear group Bellona, which states that as of six years ago, the wet storage facility at the Leningrad AES contained fuel assemblies dating back to 1975, which were then on the verge of being moved into dry storage. Given that the LAES was the first RBMK reactor, going into service in 1973, this indicates that it was never standard practice to remove spent fuel from the plants- and thus, making it impossible for the spent fuel to be reprocessed into weapons material. So even though the RBMK design is a descendant of plutonium-production reactors, it is inaccurate to characterize it in this category itself.
More than 8,700 MTHM of RBMK SNF with total radioactivity of 3.1 billion curies are stored in cooling pools at the power plants and at separate wet-storage facilities onsite. At the Leningrad Nuclear Power Station, for example, fuel is stored for three to five years in the cooling pool adjacent to the reactor building, then is loaded into a cask full of water and moved to a storage building nearby on the site (NAS 1990). Approximately 3,000 fuel assemblies are breached, which complicates handling and storage.
Dry storage is expected to replace pool storage for all of the fuel in coming years. It is anticipated that the roughly 8-meter-long RBMK fuel assemblies will have to be cut in two to fit inside the dry storage casks. Russia does not currently ship any RBMK SNF, with the exception of transportation of half-assemblies for post-reactor tests in hot cells.
The decision on the long-term plan for RBMK fuel management has not been made yet. Several approaches are possible and are now under consideration. Although accumulation of RBMK SNF at the power plant site can lead to difficulties when the plant is to be decommissioned, this spent fuel is not seen as a proliferation or an immediate health hazard, so it is the committee’s judgment that leaving it in place is a reasonable allocation of scarce resources. Nevertheless, to prevent theft for possible use in a radiological weapon, this spent fuel must be protected at the sites.