It was intended at the time of acceptance of the technical design of Paks Nuclear Power Plant, that following a three-year decay in the cooling pond, the spent fuel assemblies would be taken back to the Soviet Union on free of charge basis. The spent fuel was to be reprocessed in the Soviet Union with all reprocessing residues remaining in the Soviet Union. This was a worldwide unique service from the Soviet partner to the owner of the power plant, since the commercial reprocessing contracts all around the world prescribed the return of the end-products (uranium, plutonium, low, intermediate and high level conditioned wastes) to the country of origin of the spent fuel.
Following the commissioning of the first unit of the nuclear power plant, the conditions of the reshipment were unilaterally amended by the Soviet Union. This included the extension of the required decay period to five years and the continually increasing price of the acceptance of the returned fuel.
In its efforts to meet the new requirements, Paks Nuclear Power Plant has doubled the capacities of the cooling ponds by decreasing the lattice pitch of the storage racks, and the reshipments were managed in the framework of private contracts. Between 1989 and 1998, 2331 spent fuel assemblies were shipped back to the Soviet Union (later to Russia).
In view of the problems with the reshipments, the experts of Paks Nuclear Power Plant examined the alternative options for the storage, re-processing and disposal of the spent nuclear fuel and decided to establish a modular dry vault storage facility. In September 1992 Paks Nuclear Power Plant contracted GEC Alsthom from the UK to construct the Spent Fuel Interim Storage Facility (SFISF). The advantage of this construction is that the spent fuel is cooled by natural convection produced by the stack and the modular design allows the extension of the facility as required.
The SFISF site is situated next to the Paks Nuclear Power Plant connected to its south part. It is located in Tolna County at a distance of 118 km south of Budapest, and 5 km south of Paks on an area between the Road 6 and river Danube.
The first three modules and the reception building of the facility, which is capable (in its planned 36 modules) to store the spent fuel at least for a period of 50 years, were ready by 1997. This was followed by the hand-over of a four-vault module in 2000 and of another one in 2003.The extension in westward direction was finished in 2007 with five modules. After that the facility has been extended eastwards, and in 2012 the 17-20 modules of the SFISF were completed. The capacity of these modules was increased from 450 to 527 assemblies, thus the total storage capacity of the 20 modules of the facility is 9308 spent fuel assemblies. The commissioning of the 21-24 modules now in construction is planned for 2017.