Tritium penetration through concrete

Abstract

Concrete represents the primary barrier to migration in many proposed low-level waste storage facilities. While it may retard some dissolved ions to varying extent, it is not clear to what extent tritium movement through concrete would take place over extended periods. Experimental tests have been performed, with tritium as a tracer, on a series of concrete cylinders of a high slag aggregate composition to measure tritium mobility and to determine its dependence on concrete properties and environmental parameters. It was found that uncoated concrete absorbs water quite rapidly and once wetted, conducts tritium in water at a rate of about 8 × 10 −4 cm 3/cm 2 day. For thich specimens, over 10 cm in thickness, tritium movement is solely determined by porosity and hydraulic conductivity. Diffusion rates can be lowered by a surface finish, by using a smaller stone size in the aggregate and by vibratory compaction. Standing water may provide a hydrostatic head that results in some increase in flow rate, but it too is limited by the terminal value in hydraulic conductivity. Unless the concrete wall is coated or impregnated in some permanent fashion, it appears that little credit can be taken for the concrete walls as a retarding barrier for tritium-bearing liquids.