Granite may be used to encapsulate nuclear waste
Several years ago there was a report that a driller had struck oil in southwestern Minnesota. Minnesota’s state geologist responded simply, “Whose pipeline did they hit?” He knew that oil is rarely found in lands where basement rock is close to the surface, areas known in geology as shields. MInnesota is situated on the southern edge of the Canadian Shield.
Shields have relatively few layers of sedimentary rocks like shale from which came most of the earth’s oil and gas deposits. To our west, the basement rock dips down to form the Williston Basin which includes the western Dakotas, eastern Montana, and Saskatchewan. That basin’s deep sedimentary layers contain its large reservoir of fossil fuels.
As if to compensate for our lack of oil riches, nature provided Minnesota with substantial and useful mineral deposits, especially the world class iron ore reservoir on the Iron Range. Most of that ore is gone, having supplied the steel that framed many of America’s buildings and machines.
But in a band meandering from southwest to northeast, adjacent to the ancient Archean granite of Minnesota’s Iron Range, lie large deposits of the precious platinum group metals (PGMs) together with nickel, copper, gold, and silver. Many of these minerals contain sulfur compounds, and their exploitation is waiting more analysis of potential mining hazard to adjacent ground waters.
Minnesota is well endowed with another mineral, not precious, but widely used for buildings, bridges, paving, and countertops – granite, a tough impermeable combination of silicon and feldspar.
There is another potential use for granite, encapsulating nuclear waste. Thanks to some rigid and technically ignorant Nevada politicians, and our nation’s annual need to store thousands of tons of spent nuclear fuel, our granite could become a multi-billion dollar industry in northern Minnesota.
One-tenth of a cent per kilowatt hour (kwh) generated by our 104 nuclear power reactors is placed in a fund to provide geologic storage of the fuel waste generated by those reactors. This material is currently stored in water pools and in steel and concrete casks at our reactor sites, awaiting transfer to geologic storage..
The storage fund now exceeds $25 billion, a part of it already spent for the $10 billion-plus needed to build the long planned storage facility in Nevada’s Yucca Mountain Ridge. Now pressure from Nevada officials has caused President Obama to cancel the project and begin its dismantling.
Sandia National Laboratories was commissioned to study America’s geology for an alternate site. Sandia’s newly released report notes that granite’s properties as a chemically and physically stable rock, with low permeability, would “strongly inhibit” radiation from reaching the outside environment if waste canisters leaked. The National Academy of Sciences has also concluded that “geologic disposal remains the only scientifically and technically credible long-term solution available to meet safety needs”.
Three of the 12 promising U.S. granite sites identified in the Sandia report are in northern Minnesota. The Minnesota sites are especially effective because of low water content and our lack of seismic activity.
The other good site is in Vermont’s granite, but Vermont officials have already vetoed the idea, stating that “it should be placed in the middle of nowhere.”
The concerns in Nevada and Vermont are apparently the result of radiation fear.
The average U.S. resident receives approximately 300 annual millirems (mrems) of radiation from natural sources like radon, cosmic rays, airline flights, and eating foods like bananas and nuts which contain potassium. This radiation has occurred since humans have been on Earth, and it doesn’t hurt us, or humans would not exist. Persons who work in industries with higher radiation risk are allowed 5 rems/year, or 15 times the normal dose.
The individual-protection standard for geologic storage facilities sets an overall additional dose limit of 15 millirems per year for residents living in the vicinity of Yucca Mountain during and up to 10,000 years after the repository closes. 15 mrems is about equal to the dose received from two round trip domestic airline flights. After 10,000 years through the period of geologic stability (out to 1 million years) the individual-protection standard is set at 100 mrem/yr, a very safe level.
Opening a Yucca Mountain replacement facility in northern Minnesota is a multi billion dollar business opportunity with no significant risks to Minnesota’s people and environment. It’s an opportunity worth our consideration.
Rolf Westgard is a professional member of the Geological Society of America and the American Association of Petroleum Geologists. He teaches classes on energy subjects for the University of Minnesota Lifelong Learning program.