Corrosion of Aluminium-Clad Spent Fuel at RA Research Reactor

Almost 95% of all spent fuel elements of the RA research reactor in the Vinca Institute of Nuclear Sciences, Belgrade, Serbia and Montenegro, are stored in 30 aluminium barrels and about 300 stainless steel channel-holders in the temporary spent fuel storage water pool. The first activities of sludge and water samples, taken from the pool, were measured in 1996-1997 and were followed by analysis of chemical composition of samples. Visual inspections of fuel elements in some stainless steel tubes and of the fuel channels stored in the reactor core have shown that some deposits cover aluminium cladding. Stains and surface discolouration are noted on many of the spent fuel elements that were examined visually during the core unloading and inspections carried out in 1979-1984. Some of the water samples, taken from pool, about a 150 stainless steel tubes and 16 barrels have shown very high 137Cs activity compared with low activity measured in pool water. It was concluded that aluminium cladding of the fuel elements was penetrated due to the corrosion process. A study on the influence of water corrosion processes in the RA reactor storage pool was started within the framework of the IAEA coordinated research project entitled Corrosion of Research Reactor Aluminium-Clad Spent Fuel in Water in 2002. The first test rack with various aluminium and stainless steel coupons, supplied by the IAEA, was immersed in the pool already in 1996. New racks were immersed in 2002 and 2003. The rack immersed in 1996 was taken out from the pool in 2002 and the rack immersed in 2002 was taken out in 2003. Results of the examination of these racks carried out according to the strategy and the protocol, proposed by the IAEA, are described in the paper. (author)