Coyote Gulch

Friday, February 8, 2008

Energy policy: Nuclear

Here's another installment of their in-depth coverage of in-situ uranium mining in Texas from Fort Collins Now. From the article:

Most of the uranium in that area is gone now, after Uranium Resources Inc., where McCoig works, spent several years coaxing it out of ancient fluvial sand beds. But it will take a long time -- some opponents of URI say forever -- to clean up the groundwater with which they did it. A couple miles up Texas Highway 1118, a muddy field of newly drilled wells is starting work on the same aquifer, pumping oxygen into the groundwater to help bring out more uranium. The wells are pretty unsightly, especially given the mud that encases visitors' feet in three inches of sand-colored sludge. But after a while, the pipes that feed them will be buried under topsoil, and sorghum and cotton can once again grow. It will be harder to hear the wells' airy, gurgling sound, much like the sound of a dentist's tool used to dry out a patient's mouth, and it will be difficult to see the thick yellow cords that power the wells. In Northern Colorado, Powertech Uranium Corp. is a long way from drilling wells like these, which dot parts of Wyoming and South Texas. But once they're drilled, Powertech says its 20-year planned mining operation will barely be noticeable -- only 20 to 40 acres at a time will have well fields, and they will be re-covered with the same scrubby vegetation that grows in rural western Weld County. Many residents in Northern Colorado are opposed to Powertech's plans because the mining operation has to use groundwater from the Laramie-Fox Hills aquifer, the same aquifer that provides water to domestic and agricultural water wells in the region. But many residents don't know exactly what to expect, having never seen an in-situ uranium mine in person. With that in mind, Fort Collins Now visited Kingsville, Texas, home of URI, to see a uranium mining and milling operation...

McCoig, the senior engineer for URI, said some opponents have a "different interpretation" of some regulations, including ones that have changed since URI started mining. He and Craig Bartels, URI's vice president for in-situ mining, said the Earth's chemistry and geographical composition will help the mining companies restore the water to pre-mining conditions. "When we're done, you won't even know we were here," Bartels said. Powertech officials have taken that promise even farther, saying they may leave the aquifer better than when they found it because some dangerous materials will be removed...

About 35 million years ago, uranium-loaded volcanic ash, probably from tectonic activity in the Yellowstone National Park area, spewed into the air and settled over Wyoming and the Black Hills. Millions of years of geologic changes, including an ocean over most of the Great Plains, buried those deposits beneath Northern Colorado. The area that is now the north Front Range was a marine barrier island, evidenced by the varying layers of sand, which forms on a shoreline, and shale, which forms as organisms die, fall to the ocean floor and are compressed by heat and time. As the volcanic sediments were eroded away, oxygenated rainwater picked up the uranium on those sediments and carried it along.

In-situ mining duplicates this chemical process, by adding oxygen to the groundwater that flows around the uranium. The treated solution is called "lixiviant" and is essentially carbonated water. Powertech officials have even compared it to Perrier. In Kingsville, oxygen lasts about 12 days before it is consumed by the other materials in the rock. Powertech is still completing research to find out those numbers for Northern Colorado, but as in Texas, it will be a relatively short period before reducing agents in the rock bring the uranium back to a solid state. Those reducing agents include metals like iron, which likes oxygen, and microorganisms that use the oxygen for respiration. That might be one reason why uranium is so commonly found in coal or oil deposits, according to Mike Beshore, a Powertech geologist and the company's senior environmental coordinator. Those materials are formed from ancient carbon-based organisms compressed over eons; it's plausible that some of those critters consumed the oxygen the uranium rode in on. When the oxygen was used up in those chemical and organic reactions, the uranium came out of the water. It was left behind in the rock, and the uranium-free water kept on moving. In Northern Colorado, the water moves at a rate of roughly 12 feet per year, and Powertech consultants say it is moving northeast, toward Grover and ultimately Nebraska. The place in the rock where the uranium stopped is called a roll front, and it even looks like a roll in the rock, like a big "C" or a squiggly line of brighter color. It has been there for millions of years, embedded in the same tightly compacted sands that bear the Laramie-Fox Hills aquifer. Above and beneath the sands are even more tightly packed clays and, in Northern Colorado, that's the ancient marine shale. Powertech engineers say those layers will "confine" the aquifer so no uranium-bearing water will escape above or below the water table. What's more, the lixiviant that picks up the uranium will only take it so far before the carbonaceous material and other metals reduce the oxygen again, causing the uranium to precipitate out of the water...

Once Powertech or URI gets the uranium out of the ground, a lengthy, complicated process must take place before it can be used in a nuclear power plant -- or for any other reason. About 99.3 percent of all uranium is U-238, an isotope that means the metal has 238 neutrons. Nature wants entropy to decrease, making things more orderly and as stable as possible, so the atoms want to get rid of their extra neutrons. This is what makes uranium and other heavy metals radioactive. They need to kick off neutrons to decay into a more stable element. Uranium has 14 "daughter products" that are the progeny of this decay. Many of them are also radioactive, like radium and thorium; ultimately, uranium and its progeny decay into lead. It takes a long while for this to happen, and it can be measured in whats called half-life -- it dictates that in a given amount of time, half of the atoms in a given radionuclide will decay. The half-life of U-238 is 4.5 billion years, which makes it "barely radioactive" in the basic definition of the word. The other 0.7 percent of naturally occurring uranium, U-235, is an isotope with fewer neutrons, and it is much more radioactive -- its half-life is 760 million years. When uranium is taken from the ground and turned into yellowcake, an oxygenated, goldenrod-colored powdery form of uranium, it needs to be enriched so that more of it is made up of U-235. In the end, about 3 percent of the uranium is made into that isotope. Along the way, other potentially helpful radioactive metals are extracted from the enrichment process, like technetium-99 metastable, which is used in medical imaging. What's left can be made into uranium pellets, which are inserted into fuel rods, which go inside a nuclear reactor core. In a power plant, the core heats water that is turned into steam to power a turbine, which generates electricity. Nuclear power plants are far more efficient at making electricity than coal or gas power plants.

Read the whole article. More Coyote Gulch coverage here and here.
"2008 pres"
6:40:22 AM