Handling and behaviour of AVR fuel elements for interim storage

Between 1966 and 1984, nearly 290000 spherical fuel elements with several types of coated particles have been irradiated in the Juelich Experimental Power Plant (AVR). The spent fuel elements have been discharged from the reactor into small stainless steel canisters with a capacity of 50 pebbles each (AVR can). The AVR cans were received and racked in a pool facility of the hot cell laboratory and in the DIDO reactor with the aim for interim storage. After several years of storage in the pool, the small AVR cans were decanted in stainless steel storage canisters with a capacity of 950 fuel elements maximum (dry storage can). In addition an interim storage facility with 158 transport/storage casks (CASTOR-AVR), made of nodular cast iron, was installed. Each cask is suitable for the storage of two dry storage cans. Complementing the storage of AVR fuel, a measuring program was initiated to demonstrate the safety of dry storage of spent HTR fuel elements and to provide data for licensing commercial storage casks. It was found, that under interim storage conditions only the radioactive gaseous nuclides H-3, Kr-85 and C-14 (CO2) can be released, and as a consequence these are the principal nuclides measured in this programme. Additional gamma- and neutron dose rate measurements at the surface of the transport/storage casks were carried out. (Author)