Near-surface disposal of concentrated NORM wastes

Naturally occurring radioactive material (NORM) in concentrated forms arises in nature and in industry where natural radioisotopes become mobile and then accumulate at particular sites. In industry this often occurs in an acidic environment where precipitates containing radionuclides plate out onto pipe walls, filters, tank linings, etc. As the radionuclides are selectively deposited, they build up and there is a multiplying effect in terms of the radioactivity concentration. Conditions often tend to favour the build-up of radium, particularly when barium is present and can cause the co-precipitation of radium compounds. As radium is highly radiotoxic, the handling and disposal of such material requires careful management. The state of Western Australia currently has the only low level waste repository in Australia, located at Mt Walton East. To date this repository has been used predominantly to dispose of packaged radioactive waste containing artificial radioisotopes, but there is an increasing demand for the repository to accept bulk concentrated NORM wastes from mining and related industries. Already steelwork from a dismantled phosphoric acid plant and other items contaminated with NORM have been disposed of. The Mt Walton East repository is now proposed as the disposal site for 6000 tonnes per annum of gangue residue from the processing of monazite. The residue contains thorium and a small amount of radium. This paper looks at the technical and related considerations of these disposal operations.