US company demonstrates innovative waste disposal concept

Friday, 18 January 2019

The prototype canister, which held a steel rod to simulate the weight of radioactive waste, was lowered over 2000 feet (610 metres) into an existing drillhole using a wire cable, then pushed using an underground 'tractor' 400 feet into a horizontal storage section. The canister was released and the cable withdrawn. Several hours later, the tractor was placed back into the hole, where it latched onto and retrieved the canister, bringing it back to the surface.

The test, attended by over 40 observers including representatives from the US Department of Energy (DOE), nuclear, oil and gas industry professionals, investors, environmentalists and citizens, was the first time that Deep Isolation's prototype waste canister had been revealed in public.

Disposal in deep boreholes - narrow, vertical holes drilled deep into the earth's crust - has been considered as an option for the geological isolation of radioactive wastes since the 1950s. Deep borehole concepts have been developed in countries including Denmark, Sweden, Switzerland, and the USA but have not yet been implemented.

In 2016, a team led by Battelle Memorial Institute was selected by the DOE to drill a 16,000 feet test borehole into a crystalline basement rock formation in North Dakota as part of studies into the feasibility of using boreholes for nuclear waste disposal. The same year, the International Atomic Energy Agency announced the completion of 'proof of concept' tests for borehole disposal of small volumes of radioactive waste. However, the concept has generally been considered to be an expensive option for large volumes of wastes compared to a mined underground repository, and borehole disposal has not previously been considered to be retrievable.

Deep Isolation's patented technology leverages standard drilling technology using off-the-shelf tools and equipment that are common in the oil and gas drilling industry. The company last November carried out tests of its equipment, tools, and methods at a commercial testing facility for oil and gas drilling.

It envisages emplacing nuclear waste in corrosion-resistant canisters - typically 9-13 inches (22-33 centimetres) in diameter and 14 feet long - into drillholes in rock that has been stable for tens to hundreds of millions of years. The drillhole - which is lined with a steel casing - begins with a vertical access section which then gradually curves until it is nearly horizontal, with a slight upward tilt. This horizontal 'disposal section' would be up to two miles (3.2 kilometres) in length and lie anything from a few thousand feet to two miles beneath the surface, depending on geology.

Once the waste is in place, the vertical access section of the drillhole and the beginning of its horizontal disposal section would be sealed using rock, bentonite and other materials.

The key advantages of the 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, the company says. In addition, small diameter drillholes require less disturbance of the rock than a mined repository.

Deep Isolation Chief Technology Officer Richard Muller said the company was using existing drilling technology for an "unexpected and extremely important" new application.

"Right now, the US is holding 80,000 tons of highly radioactive nuclear waste. Something must be done with this, and every major scientific group that has studied the challenge concluded that putting it deep underground is the safest solution for the present and future generations," he said. "A drilled repository allows you to go deeper while disturbing less rock. It is both safer and less expensive than a mined repository."