Direct ultimate disposal of spent fuel elements. Preparatory tests for selection of a suitable packing method

The pneumatic packing method and the slinger stowing method have been tested under boundary conditions valid for an ultimate disposal site, and have been evaluated quality. Two test series have been made, accompanied by extensive sampling work and analyses of the soil-physical parameters. In-situ ground density measurements have been made with a gamma-gamma probe. Within a given period of observation (2-2 days), no compaction of the material in the roof area could be detected. In the test site packed by the pneumatic method, some wave-shaped cavities of only a few centimetres in depth have been observed at the roof, which are attributed to an unprecise alignment of the pneumatic pipe during packing. Apart from this, the material could be positioned and packed flushing to the roof, also with the slinger method. No cavities could be detected between the containers, or at the bottom sides. Dust suppression through addition of liquids during pneumatic packing is a standard technique and well feasible with the commercially available equipment. As regards the slinger stowing method, there is no established process available yet, but it seems possible to solve the dust problem by means of some technical design modifications at the throwing belt and, where the liquid could be added to the packing material flow so that the dust is sufficiently suppressed. (orig./HP)