Radioactive waste: Where to put it?

As the U.S. makes new plans for disposing of spent nuclear fuel and other high-level radioactive waste deep underground, geologists are key to identifying safe burial sites and techniques. Scientists at The Geological Society of America (GSA) meeting in Denver will describe the potential of shale formations; challenges of deep borehole disposal; and their progress in building a computer model to help improve understanding of the geologic processes that are important for safe disposal of high-level waste.

In the United States, about 70,000 metric tons of spent commercial nuclear fuel are located at more than 70 sites in 35 states. Shales and other clay-rich (argillaceous) rocks have never been seriously considered for holding America’s spent nuclear fuel, but it is different overseas. France, Switzerland, and Belgium are planning to put waste in tunnels mined out of shale formations, and Canada, Japan, and the United Kingdom are evaluating the idea.

At the GSA meeting, U.S. Geological Survey hydrogeology expert C.E. Neuzil of Reston, Virginia, will report that some shales are so impermeable that there is little risk of radioactivity from buried nuclear waste reaching ground or surface water.

“This is usually difficult to demonstrate,” Neuzil says, “but some shales have natural groundwater pressure anomalies that can be analyzed — as if they were permeability tests — on a very large scale.” This capability was shown recently at the Bruce Nuclear Site, explains Neuzil, a proposed low/intermediate waste repository 1,200 feet underground in Ontario, Canada. Argillaceous rocks have additional attractive qualities, Neuzil says: They are common, voluminous, and tend to be tectonically quiet — meaning no earthquakes to crack the walls of a fuel-rod burial chamber.

Another disposal option for nuclear waste is deep boreholes. The 2012 presidential Blue Ribbon Commission on America’s Nuclear Future recommended more research, and the U.S. Department of Energy is now developing an R&D plan. However, the U.S. Nuclear Waste Technical Review Board (NWTRB) has statutory responsibility for evaluating the technical validity of DOE’s nuclear waste activities, and is on the record with the position that deep boreholes present many technical challenges and studying them “should not delay higher priority research on a mined geologic repository.”

At next week’s GSA meeting, Review Board senior staff professional Bret W. Leslie and Stanford University geophysicist Mary Lou Zoback, an NWTRB member, will present the board’s assessment of:

  • the technical feasibility of drilling a borehole of the proposed depth (3 miles) and width (about 20 inches), which has never been done;

  • the exposure risk for workers, who would have to repackage waste currently stored in canisters that are wider than the width of the proposed boreholes;
  • the reliability of existing sealing technology; and
  • the large number of deep boreholes that would be required — nearly 700.

Whether nuclear waste winds up in tunnels, boreholes or both, the planning will be helped by new analytical tools. One is a new computer model that will evaluate the behavior of various forms of nuclear waste, and waste containers and barriers, if stored in various rocks. The model is being developed under the auspices of the Center for Nuclear Waste Regulatory Analyses (CNWRA), the NRC’s federally funded research and development center, and will be described at the GSA meeting by NRC performance analyst Jin-Ping Gwo.

Rio Grande rift: From tectonics to groundwater, north to south

This is the cover of GSA Special Paper 494: New Perspectives on Rio Grande Rift Basins: From Tectonics to Groundwater. -  Mark R. Hudson and V.J.S. (Tien) Grauch (editors)
This is the cover of GSA Special Paper 494: New Perspectives on Rio Grande Rift Basins: From Tectonics to Groundwater. – Mark R. Hudson and V.J.S. (Tien) Grauch (editors)

Extending from Colorado, USA, to the state of Chihuahua, Mexico, the Rio Grande rift divides the Colorado Plateau on the west from the interior of the North American craton on the east. The rift is named after the Rio Grande, the major river that flows through most of its extent, from southern Colorado, through New Mexico, and along the border between Texas, USA, and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas.

Individual valleys of the Rio Grande rift are easy to recognize to the north, but more difficult in the Basin and Range in southern New Mexico, west Texas, and northern Mexico. This new book from The Geological Society of America focuses on the Rio Grande rift’s upper crustal basins.

Editors Mark R. Hudson and V.J.S. (Tien) Grauch of the U.S. Geological Survey have organized the book geographically, with study areas progressing from north to south. Eighteen chapters cover a variety of topics, including sedimentation history, rift basin geometries and the influence of older structure on rift basin evolution, faulting and strain transfer within and among basins, relations of magmatism to rift tectonism, and basin hydrogeology.

What lies beneath the seafloor?

An international team of scientists report on the first observatory experiment to study the dynamic microbial life of an ever-changing environment inside Earth’s crust. University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science professor Keir Becker contributed the deep-sea technology required to make long-term scientific observations of life beneath the seafloor.

During the four-year subsurface experiment, the research team deployed the first in situ experimental microbial observatory systems below the flank of the Juan de Fuca Ridge, which is located off the coast of Washington (U.S.) and British Columbia (Canada).

Becker and UM Rosenstiel alumnus Andrew Fisher installed the sub-surface observatory technology known as CORK (Circulation Obviation Retrofit Kit), which seals the sub-surface borehole for undisturbed observations of the natural hydrogeological state and microbial ecosystem inside Earth’s crust.

“Similar to a cork in a wine bottle, our technology stops fluids from moving in and out of the drilling hole,” said Becker, a UM Rosenstiel School professor of marine geology and geophysics. “Ocean water is blocked from entering the hole and flushing out the natural system.”

These natural laboratories allow scientists to investigate the hydrogeology, geochemistry, and microbiology of ocean crust.

A large reservoir of seawater exists in Earth’s crust, which is thought to be the largest habitat on Earth. This seawater aquifer supports a dynamic microbial ecosystem that is known to eat hydrocarbons and natural gas, and may have the genetic potential to store carbon. Scientists are interested in better understanding the natural processes taking place below the seafloor, which also give rise to economically important ores along the seafloor and may play a role in earthquakes.

“The paper is important since it is the first in-situ experiment to study subsurface microbiology,” said Becker, a co-author of the paper.