URANIUM DISPOSAL CELLS were the subject of an exhibit opened at the CLUI Los Angeles in June 2012. The exhibit featured glowing LCD screens with black and white images of a selection of the engineered mounds, taken by the CLUI over the last year, and touchscreen maps that provided more images and information about these structures across the country.
Uranium disposal cells are unusual constructions because they are built to last far beyond the lives of most engineered structures, to isolate their radioactive contents from the environment for hundreds of years. They are generally low geometric mounds, sometimes as high as a hundred feet tall, covering a few acres or as much as a half mile, and composed of layers of engineered soil and gravels designed to shed rainwater and limit erosion, in order to take their contents, intact, away from the present and as far into the future as possible.
The contents are not considered high-level radioactive waste, like spent fuel from nuclear reactors. That material has yet to find a permanent home. What these cells contain is radioactive tailings from uranium processing sites, as well as the demolished buildings and apparatus from the mills themselves. The amount of radioactivity in these cells varies, but is generally considered harmful to people if exposure takes place over sustained periods. Most of the radiation comes from uranium 238, which has a half life of 4.47 billion years, nearly the age of the earth itself.
Sometimes the disposal cell is built at the site of a closed-down uranium mill, but in most cases the cell is constructed a few miles from the mill site, in a location that is more distant from communities and waterways, and the material is trucked to the site for burial.
Though anomalous and distinct in their form from their surroundings, the cells are meant to blend in geomorphologically, to integrate with the forces of drainage and erosion of the landscape. In arid environments, the outer shell is a layer of coarse riprap rock, golfball to softball sized stones a foot or two thick. Beneath this is a clayey soil layer, a few feet thick, which covers the radioactive material below. When rain falls, the water passes through the riprap, then flows over the top of the less permeable clay layer, and down the sides of the pile, where troughs and channels take it away from the structure. The riprap is a carapace, holding the clay beneath it in place, and it also reduces the collection of organic material on top of the mound and the development of soil that would lead to growth of plants whose roots could eventually penetrate the clay layer. The low angle of the sides of the mounds, less than the angle of repose, keep the rock in place, and the form of the mound intact.
In places with higher rainfall, the tops of the mounds are sometimes covered in soil, not riprap, and planted with grass. The soil and plants act as a sponge, soaking up the rain, and slowing down the runoff which would otherwise form channels, and eventually erode the clay barrier beneath. The soil and grass also reduce runoff by evaporating and transpiring moisture into the air. The shallow roots from the planted grass help keep the soil in place, while other plants that might sprout unintentionally, with potentially deeper roots, are extracted from the soil through regular maintenance of the pile.
The cells tend to be in arid regions in the southwest, as this is where the uranium was mined and milled: northwest New Mexico, western Colorado, and southeastern Utah, especially. But they were built elsewhere, too, as uranium mining and milling occurred in other states such as Texas, Washington, Oregon, and Wyoming. Uranium metal processing and engineering took place in dozens of states, including Massachusetts, New York, Pennsylvania, Missouri, West Virginia, and Ohio. In some cases factories involved in the process of milling uranium have been razed and transported across the country for disposal in arid land disposal cells. In other cases, the factory site was bulldozed into a mound, capped, and left for the future.
Many of the mills from the uranium boom years sat abandoned for decades, with the radioactive tailings and salvaged parts from the mill used as construction materials in the surrounding communities. In some places, the mounds of sandy-textured tailings were used to make concrete for sidewalks, patios, parking lots, houses, and even schools. These structures later had to be identified and torn down as part of the clean-up process, and the remains moved into these mounds.
Most of these piles were made by contractors for the Department of Energy in the late 1980s and early 1990s, when the government took over handling the wastes left by companies, in some cases bankrupted by the process, or otherwise no longer existing or accountable. The government was, after all, the reason these sites existed in the first place, since in the early years of the industry they were the only customer for uranium–using it to build atomic bombs.
Dozens of uranium mills were constructed in the 1940s and 1950s, dating back to the Manhattan Project, exclusively to supply the material for reactors used in weapons production, and in the weapons themselves. While the government-propelled uranium prospecting and mining boom ended in the 1960s, once supplies for atomic weapons were met, some of these sites continued to operate for the atomic power industry, which uses uranium as fuel in nuclear reactors. A number of these uranium mills continued to operate until the 1990s. Today there are only a couple of active uranium mines in the nation, and only one active commercial uranium mill.
Disposal cell construction started in the late 1980s, and it continues to this day. The original mill sites, as well as the disposal cells, are managed by the Department of Energy’s Legacy Management Office, which was created in 2003 to care for these sites indefinitely into the future.
The office also takes on responsibility for long-term monitoring for some other uranium and non-uranium related contaminated sites around the country, those that had the federal government as a customer, after they get closed and cleaned up by the companies that owned and operated them. The Legacy Management Office currently manages more than 100 sites, a list that is growing.