Development of a waste-containing unit for use in shallow-land burial

The purpose of this investigation is to try to improve the safety of disposal of low- and medium-level radioactive waste in man-made constructions placed below ground but near the surface. A standard waste unit of hexagonal shape has been developed. Empty containers without lids are prefabricated from reinforced concrete. The waste is placed in the container - using remote control if necessary - and a lid is cast directly on top of the waste. The hexagonal shape was selected since it is suitable for an overpack container used for standard 210 L drums and since such units can be placed together with very little space between them. This space is supposed to be filled with bitumen or concrete after placing the unit in the repository. One option under investigation in the study is to make the units of a new type of concrete called Densit, which has a much higher compression strength than ordinary concrete. The diffusivity for dissolved ions in the material is low, and the electrical resistivity is high. The material will therefore act as an additional barrier against migration of radioisotopes from the waste. More important, from a safety point of view, is that the disposal system as a whole is supposed to prevent contact between waste and water for a very long time. Preliminary results from laboratory investigations of the properties of the new material are reported. (author)