What is the Deep Isolation concept, in simple terms?
Deep Isolation will emplace nuclear waste in corrosion-resistant canisters (typically 9 to 13 inches in diameter and 14 feet long) deep into horizontal drillholes, in rock that has been stable for tens to hundreds of millions of years.
A Deep Isolation drillhole begins with a vertical “access” section that goes down from a few thousand feet to a few miles, depending on the geology. The drillhole then gradually curves, over a distance of typically 1000 feet, until the hole is near horizontal. (We give it a slight upward tilt for additional safety.) This (nearly) horizontal part we refer to as the “disposal” section.
Once the waste is in place, the vertical access section of the drillhole and the beginning of its horizontal disposal section are sealed using rock, bentonite and other materials.
Virtually all committees of scientists convened to study the disposition of nuclear waste have concluded that deep geologic burial (1000 feet or more) is the best disposal solution. Most previous approaches have assumed this requires large excavated tunnels for emplacement of the waste.
The key advantages of the Deep Isolation method are the depth of burial and the fact that the waste is stored in a suitable geologic formation far below the water table, in rock that is saturated with brine that has no commercial value and has been virtually stagnant for millions of years. In addition, the small diameter drillholes require less disturbance of the rock than a mined repository.
The horizontal drilling technology that will be used is highly developed and can be implemented at a relatively low cost. It can be modular, thus minimizing transportation concerns by allowing disposal at or near the generation site. Cost and safety are also improved by the fact that no person needs to go underground during construction.
The horizontal disposal section could be up to 2 miles long. With horizontal disposal sections this long, it would take 300 such horizontal drillholes to dispose of 80,000 tons of commercial spent nuclear fuel.