Deep borehole disposal (DBD) is the concept of disposing high-level radioactive waste from nuclear reactors in extremely deep boreholes instead of in more traditional deep geological repositories that are excavated like mines. Deep borehole disposal seeks to place the waste as much as beneath the surface of the Earth and relies primarily on the thickness of the natural geological barrier to safely isolate the waste from the biosphere for a very long period of time so that it should not pose a threat to humans and the environment. The concept was originally developed in the 1970s, but in 2014, a proposal for a first experimental borehole was proposed by a consortium headed by Sandia National Laboratories. The waste would be put into the lower mile of such a hole, within crystalline rock to isolate it from the environment. The upper two miles of the borehole would be filled with protective layers including asphalt, bentonite, concrete, and crushed rock that are expected to protect the environment during geologic time, and the hole would be lined with steel casing. A pair of proposed test boreholes in the United States were cancelled due to public opposition and lack of funding in 2016 and 2017. American deep borehole disposal tests Beginning in 2016, the U.S. Department of Energy funded an experimental borehole extending over deep, in Rugby, North Dakota. The plans for this five-year project in Rugby did not involve nuclear waste, and instead would have tested other aspects of the borehole concept. However, following protests in North Dakota, a site was proposed in Spink County, South Dakota. After protests in South Dakota prevented the project from moving forward, the Department of Energy scrapped the project. Due to public opposition to the first experimental borehole, in late 2016, the Department of Energy announced a second project which would have involved four sites: two in New Mexico, one in Texas, and one in South Dakota. The early stages of the project required gaining public support before the Department of Energy would have selected a final site for an experimental borehole. On 23 May 2017, the Department of Energy announced that funding priorities had changed and that the deep borehole project was de-funded. Illustration In the diagram, the solution domain is used for the purpose of computer modelling of heat flow around the borehole. Details Deep borehole disposal involves drilling a hole about down into the