Deep borehole disposal
Encyclopedia
Deep borehole disposal is the concept of disposing of high-level radioactive waste
from nuclear reactors in extremely deep borehole
s. Deep borehole disposal seeks to place the waste as much as five kilometers 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 man and the environment. In the diagram the solution domain is used for the purpose of computer modelling of heat flow around the borehole.
, like spent nuclear fuel
, would be sealed in strong steel
containers and lowered down the borehole, filling the bottom one or two kilometres of the hole. The rest of the borehole is then sealed with appropriate materials, including perhaps clay, cement, crushed rock backfill, and asphalt, to ensure a low-permeability barrier between the waste and the land surface. In some concepts, waste may be surrounded by cement
itious grout or a highly-compacted bentonite
buffer matrix to provide improved containment and to attenuate the impact of rock movements onto the canisters integrity. 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. Under both scenarios, chemically reducing conditions adjacent to the borehole will reduce the transport of most radionuclides.
The deep borehole concept can be applied to any amount of waste. For countries that do not rely on nuclear power plants, their entire inventory of high-level nuclear waste could perhaps be disposed of in a single borehole. Current estimates suggest that spent fuel generated from a single large nuclear power plant operating for multiple decades could be disposed of in fewer than ten boreholes. Borehole disposal programs could be terminated at any time with little loss of investment because each borehole is independent. The modular nature of borehole disposal would lend itself to regional, or on-site, disposal of nuclear waste. Another attraction of the deep borehole option is that holes might be drilled and waste emplaced using modifications of existing oil and gas drilling technologies.
Finally, the environmental impact is small. The waste handling facility at the wellhead
, plus a temporary security buffer zone, would require about one square kilometer. When the borehole is filled and sealed, the land can be returned to a pristine condition.
Radioactive waste
Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...
from nuclear reactors in extremely deep borehole
Borehole
A borehole is the generalized term for any narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation, environmental site...
s. Deep borehole disposal seeks to place the waste as much as five kilometers 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 man and the environment. In the diagram the solution domain is used for the purpose of computer modelling of heat flow around the borehole.
Illustration
 |
Details
The concept involves drilling a borehole about 5 km down into the Earth's crust. High level wasteHigh level waste
High level waste is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:* First and second cycle raffinate and other waste streams created by nuclear reprocessing....
, like spent nuclear fuel
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...
, would be sealed in strong steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
containers and lowered down the borehole, filling the bottom one or two kilometres of the hole. The rest of the borehole is then sealed with appropriate materials, including perhaps clay, cement, crushed rock backfill, and asphalt, to ensure a low-permeability barrier between the waste and the land surface. In some concepts, waste may be surrounded by cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
itious grout or a highly-compacted bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
buffer matrix to provide improved containment and to attenuate the impact of rock movements onto the canisters integrity. 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. Under both scenarios, chemically reducing conditions adjacent to the borehole will reduce the transport of most radionuclides.
The deep borehole concept can be applied to any amount of waste. For countries that do not rely on nuclear power plants, their entire inventory of high-level nuclear waste could perhaps be disposed of in a single borehole. Current estimates suggest that spent fuel generated from a single large nuclear power plant operating for multiple decades could be disposed of in fewer than ten boreholes. Borehole disposal programs could be terminated at any time with little loss of investment because each borehole is independent. The modular nature of borehole disposal would lend itself to regional, or on-site, disposal of nuclear waste. Another attraction of the deep borehole option is that holes might be drilled and waste emplaced using modifications of existing oil and gas drilling technologies.
Finally, the environmental impact is small. The waste handling facility at the wellhead
Wellhead
A wellhead is a general term used to describe the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment....
, plus a temporary security buffer zone, would require about one square kilometer. When the borehole is filled and sealed, the land can be returned to a pristine condition.
External links
- Journal of the Geological Society, Jan 2000 by Gibb, Fergus G F
- Nirex Report : A Review of the Deep Borehole Disposal Concept for Radioactive Waste
- Hoag/MIT Thesis - Canister Design for Deep Borehole Disposal of Nuclear waste
- Sandia National Labs' Performance Assessment of Deep Boreholes
- Sizer/MIT Thesis - Minor Actinide Waste Disposal in Deep Geological Boreholes
- 2010 NEI Deep Borehole Article
- 2010 Physics Today Deep Borehole Article
- March 2010 Driscoll Presentation at Sandia-MIT Borehole Workshop