A number of countries, including Australia, Russia, South Africa and the USA, have practised and, in some cases, continue to practise, disposal of radioactive waste in boreholes or shafts of various sizes. In the case of the USA, this even extends to transuranic waste. In addition, the prospect of using very deep boreholes for disposal of spent fuel has continued to attract attention over a period of more than 30 years (e. g. Ref. 39). More recently, however, of boreholes have come to be seen as a potential solution for the long-term safety of disused sealed sources. In particular, the IAEA has developed the so-called BOSS system, 1 0 which aims to provide a safe, permanent solution for those many countries that use sealed sources but have no nuclear infrastructure that would enable them to be managed safely after use. A particular problem has arisen with radium sources that, until 30 or 40 years ago, were widely used in medical therapy. Because the half-life of radium-226 is 1600 years, the radioactivity of these sources has hardly diminished in the interim and they now constitute a dangerous waste and a potential security hazard.

The BOSS system provides double containment of disused sources in stainless steel, burial at more than 30 m depth and encasement in concrete. Under anaerobic conditions (commonly found at depth), the combination of stainless steel and concrete is capable of providing absolute physical containment for at least 200 000 years, which is more than sufficient to allow radium-226 sources to decay to below exemption level. The system is small scale and economical. Considering the deaths that have occurred from loss of control of disused sealed sources over the years, it has the potential to provide significant benefits in terms of public safety and security.