Within the Croatian RD & D program for low- and intermediate-level waste and spent nuclear fuel disposal, research of the permeability and diffusion of tritium in bentonite was organized, as part of the research of the future engineering barriers for repositories. Pure sodium bentonite and a mixture of sodium bentonite with quartz sand were prepared. Compaction of materials was conducted with a modified Proctor test, and the apparatus was designed and made at the University of Zagreb.