Wet and Semi-Dry Storage of Spent Nuclear Fuel at the Budapest Research Reactor

In the frame of the Russian Research Reactor Return Programme the spent nuclear fuel assemblies (SNFAs) of the Budapest Research Reactor (BRR) irradiated prior to 2005 were shipped back to the country of origin. Since the time of the reactor's first criticality in 1959 these SNFAs were stored in the At-reactor (AR) and Away from reactor (AFR) pools of the reactor. Fuel assemblies stored at the BRR site were noted as being in good condition following fuel characterization and observations performed prior to and during loading. The good condition of the SNFAs was due, amongst other things, to the well-controlled water quality in the storage pools, the periodic visual inspections, but mostly to the encapsulation of SNFAs that changed the temporary storage mode from wet to semi-dry. In accordance with the encapsulation technology and storage mode, the encapsulated fuel assemblies (packages) were kept in the same pool under water but the fuel was maintained in dry conditions, namely in an inert gas atmosphere. Therefore a safe, extended temporary storage was ensured until the assemblies were transported to their place of final disposal. The cladding of repacked fuel demonstrated that the applied encapsulation technology had slowed down or even stopped the corrosion effects of the cladding and thereby ensured safe extended storage conditions. This paper introduces the storage modes (practice of water chemistry and applied monitoring techniques) and gives a detailed description of the canning technology used. It also details experiences gained during the canning and the storage phases of the encapsulated fuel. The paper focuses less on the wet storage problems of SNF and more on the canning technology and the canning equipment itself, as well as on the repacking experiences gained during the transport container loading. Finally the paper draws some concluding remarks on lessons learned. (author)