Deep Borehole Disposal is the concept of disposing of high-level radioactive waste from nuclear reactors in extremely deep boreholes. Deep borehole disposal seeks to place the waste as much as five kilometers beneath the surface of the Earth and relies primarily on the immense natural geological barrier to do most of the work of confining the waste safely and permanently so that it should never pose a threat to the environment. In the diagram the solution domain is used for the purpose of computer modelling of heat flow around the borehole. [1]
Details
The concept involves drilling a borehole about 5 km down into the Earth's crust. High Level Waste, like spent nuclear fuel, is sealed in strong steel containers and pushed down the borehole, filling the bottom of the hole one or two km. The rest of the borehole is then filled with backfill, such as crushed granite and water or, in some scenarios, cementitious grout or a high-density support matrix to provide improved containment and to ensure the containers will never rupture under the enormous pressures. A high-temperature scenario involves very young hot waste in the containers which releases enough heat to create a melt zone around the borehole. As the waste decays and cools, the melt zone resolidifies, forming a solid granite sarcophagus around the containers, entombing the waste forever. [2]
The deep borehole concept can be applied to any amount of waste. Some countries may need only one borehole to dispose of all their waste. Other countries may need to embark on a multiple borehole program. The program can be terminated at any time with little loss of investment and those boreholes already drilled can still be used for waste disposal because each borehole is independent.
Finally, the environmental impact is small. The waste handling facility at the well head, plus a temporary security buffer zone, would require about one square kilometer. When the borehole is filled and sealed, the land is supposed to be returned to a pristine condition.
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