Why have a horizontal borehole? If you have a shale layer that is hundreds of meters thick, is it not much less risky and cheaper to put it into a vertical hole?

We believe a horizontal borehole repository has some safety features that are inherent in its design, reducing overall risks and providing enhanced long-term safety. Horizontal boreholes allow waste canisters to be installed end-to-end in a row. In the vertical scenario, stacking loads are considerable and need to be mitigated by installing numerous engineered supports or plugs every few canisters. In addition, in the horizontal concept, the waste disposal section is off-set from the vertical access hole. Moreover, driving forces needed for radionuclide transport along the horizontal borehole axis would be perpendicular to (i.e., not aligned with) the more critical vertical gradients. Finally, most shale formations have limited vertical thickness but are horizontally extensive.