IAEA's safety review of Vinca's spent fuel repackaging operation

The RA research reactor, at the 'Vinca' Institute of Nuclear Sciences approximately 15 km South-East of downtown Belgrade, has been in extended shut down since 1984. In 2002 the Serbian Government decided to shut down the reactor permanently and to participate in the Global Threat Reduction Initiative (GTRI) Russian Research Reactor Fuel Return (RRRFR) programme to repatriate fresh and irradiated (spent) fuel back to the Russian Federation, the country of origin. The existing irradiated TVR-S Russian type fuel elements, with enrichments of 2% (metal uranium composition) and 80% (UO2-Al), were stored in special containers in the spent fuel storage basin in the reactor building or in stainless steel channel holders. A TVR-S element has a diameter of 40.4 mm, is 113 mm long and contains 7.2 grams 235U or 7.7 235U for respectively 2% or 80% enrichment. In total 4929 fuel elements are stored in 30 aluminium (Al) barrels and each barrel contains 30 Al-tubes with 5 or 6 fuel elements each. The other 3101 spent fuel elements are stored in 297 stainless steel channel holders (SSCH). Each SSCH contains one aluminium tube with maximum 12 fuel elements. Due to a poor water quality of the spent fuel storage basin, the aluminium cladding of a number of the spent fuel elements degraded, resulting in fission products leaking from the fuel elements into the storage containers and, in some cases, into the fuel storage pool. Environmental monitoring did not show evidence of any leakage to the environment. Repackaging of the fuel into special stainless steel (SS) canisters, which will be loaded in two different types of transport containers, is needed to ensure their safe transport. The relatively complex structure of the original containers, the degraded fuel elements, and the high contamination of the spent fuel basin water made the repackaging a rather complex operation. After repackaging of the fuel elements they have to be stored in the spent fuel storage basin at the site before they can be loaded into the transport containers. A new Serbian Law was issued on 12 May 2009 by which a new Agency for Ionizing Radiation and Nuclear Safety of the Republic of Serbia (Serbian Regulatory Authority: SRA) was established. The SRA replaced the Serbian Regulatory Commission (SRC) which was created in April 2005. The law required also that all nuclear liabilities and assets have to be transferred, from the Vinca Institute of Nuclear Sciences, to a new Public Company Nuclear Facilities of Serbia (PC NFS), including the responsibility for the research reactors, spent fuel and radioactive waste management at the Vinca Institute. The fresh TVR-S fuel elements, which were stored at the RA and RB reactor, were repatriated to Russia in August 2002, and are not discussed in this paper