Geological disposal of HLW and spent nuclear fuel (SNF) in very deep boreholes is a concept whose time has come. The alternative – disposal in a mined, engineered repository is beset with difficulties not least of which are the constraints placed upon the engineered barriers by the high thermal loading. The deep borehole concept offers a potentially safer, faster and more cost-effective solution. Despite this, international interest has been slow to materialize, largely due to perceived problems with retrievability and uncertainty about the ability to drill accurate vertical holes with diameters greater than 0.5 m to a depth of 4-5 km. The closure of Yucca Mountain and the subsequent recommendations of the Blue Ribbon Commission have lead to a renewed interest in deep borehole disposal (DBD) and the US DoE has commissioned Sandia National Labs, working with industrial and academic partners (including the University of Sheffield), to undertake a program of R&D leading to a demonstration borehole being drilled somewhere in the continental USA by 2016.
In this paper, we focus on some of the key safety and engineering features of DBD including methods of sealing the boreholes, sealing and support matrices for the waste packages. Numerical modeling has, and continues to play, a significant role in expanding and validating the DBD concept. We report on progress in the use of modeling in the above contexts, paying particular attention to constraints on the engineering materials resulting from high heat loading.