The concept of using deep borehole repositories for permanent isolation of radioactive materials has been proposed and investigated intermittently for decades (see Refs. 1-9 and Further Reading). The earliest proposals for deep borehole disposal considered direct disposal of liquid high-level wastes from reprocessing;1 subsequent analyses have considered disposal of solid wastes of various types, including glass HLW, spent nuclear fuel, and surplus weapons-grade plutonium. Although published analyses to date have concluded that the overall concept has the potential to offer excellent isolation, disposal programs worldwide have focused on mined repositories, in part because of the availability of proven mining technologies at the time that national policy decisions were made and in part because of concerns about the feasibility of retrieving waste from deep boreholes. Advances in drilling technologies over the last several decades suggest that the construction of deep boreholes should no longer be viewed as a greater technical challenge than deep mines and that retrieval, if required, should not be viewed a priori us unachievable. Retrieval of wastes is likely, however, to remain more difficult from deep boreholes than from some mined repositories, and if permanent disposal is not intended, deep boreholes may not be a preferred option.
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