National Report of the Slovak Republic - Radiation and Nuclear Safety , September 1998

2.5.1 Description of Technology Used

THE ISFS represents a nuclear installation serving to temporarily and safely store spent nuclear fuel from WWER reactors prior to its further processing in a re-processing plant, or prior to its final disposal in a repository. It was commissioned in 1986 due to the termination of the contract on transport of spent fuel from WWER NPPs on the part of the Russian Federation.

The ISFS premise is a detached building with no structural links to other premises of the power plant area. The building is subdivided into the container and storage area. The storage area is comprised of 4 storage ponds, one of them being a stand-by pond. The storage ponds are connected to the transfer channel. The individual ponds can be separated from the transfer channel using hydro-valves. The transfer canals represent a continuation of the reception and reloading well which also can be separated by hydro-valves. Spent fuel is stored under water which also serves as shielding and removes the remaining thermal output.

The ISFS building has its own cooling and purification plant. The cooling plant is comprised of 3 heat exchangers, which can be either serially or parallel connected, and two ponds water pumps. The cooling plant is operated periodically according to the need to cool pond waters and to keep them within the required range of temperatures.

The purification plant keeps the quality of pond waters within the set range of parameters by mechanical filtering and ion exchange. It is being operated on a periodical basis.

ISFS receives spent fuel after approx. 3 years of cooling in the ponds at the reactor.

Spent nuclear fuel transport from NPP units uses C-30 type shipping container and special railroad cars. The C-30 type Shipping container is then moved from the transport railroad corridor to the reception well using a 130 t crane and special transfer beam. After special handling in the reception well, container de-sealing and lid removal, the cylindrical cask T-12 (T-13) with the spent fuel is moved, using a 16 t crane, to the respective position in the storage pond.

The overall storage capacity of ISFS is 5,040 pcs of fuel assemblies (approx. 600 t heavy metal), and is currently used to 88 %.

Originally, ISFS was designed for 10 years of storage of spent fuel which would then be transported to the USSR for re-processing. For a certain period of time, ISFS was also used to store spent fuel from NPP Dukovany, Czech Republic. The latter was then gradually transported back to NPP Dukovany within 1996-1997 as soon as the construction of a storage site was completed in the Czech Republic.

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