A nuclear waste repository not only has the responsibility to contain radioactivity, but it has to do so for tens of thousands—even millions—of years. The design of such a facility needs to allow the repository to do its job with as little disturbance to the outside world as possible. The bunkers of these sites are an enormous undertaking.
This Valentine's Day, a puff of radioactive contamination escaped a salt mine that is now the Nuclear Waste Isolation Pilot Plant in New Mexico. A series of automatic triggers were quickly set into action to isolate the contaminated air, yet there's worry that a small wisp may have been released into the community. Officials say that "the quantities released are far below the levels at which the Environmental Protection Agency would recommend any action." Yet given that this took place while the repository was still operational, what's to say that such facilities will be able to withstand even a fraction of the radioactive half-life they have waiting for them?
Through the tunnels of the New Mexico mine. Image via New York Times.
The design of a typical nuclear repository follows a strict trajectory: The waste is taken to a series of underground storage chambers fortified with engineered barriers at least 300 meters below ground. The geologic environment of the site needs to be stable, and there must be no exposure to groundwater. Salt mines are a popular residence since salt is not only a "stable" mineral but also "plastic"; that is, it shifts a few inches every year, potentially sealing up the waste all by itself with this "salt creep." Other sites are set in minerals such as granite, clay, limestone, and ignimbrite. At the end of the day though, these facilities are essentially fancy holes in the ground; in their final moments, the canisters are bulldozed into a giant pile at the bottom of a pit.
Spent nuclear rods at the Hansford site in Washington are stored uncapped underwater, since the US has no large-scale high-level repository location. Image via Wikimedia Commons.
However, these cannot be just any canisters in any repository. Nuclear waste is classified on a scale from low-level to high-level, depending on how long its half-life is. Low-level waste consists of mainly water and used equipment, while high-level includes spent uranium fuel rods. Currently, repositories are only capable of handling low and medium levels of waste, and there are no facilities for the storage of high levels.
Image via Wikimedia Commons.
Waste Isolation Pilot Plant
This site is used for the disposal of low- to medium-level waste that comes from the production and research of nuclear weapons around the country. The repository at the old salt mine has been in operation for the past 15 years, burying waste into a now evaporated sea under the desert. Once a certain threshold has been reached, the plan is to collapse and seal the storage caverns with 13 layers of concrete and soil. Salt will naturally seep into the cracks of the mass. In 75 years, the waste will supposedly be totally isolated.
Seeing as there would still be a few (thousand) years before it would even reach it's half-life, the facility is also developing a graphic warning system with the help of linguists, anthropologists, materials scientists, science-fiction writers, and futurists. The plan is to eventually etch these designs into granite pillars that will be installed around the facility.
Yucca Mountains. Image via Wikimedia Commons.
The proposed design for the Yucca Mountain Repository. Image via Wikimedia Commons.
Yucca Mountain Nuclear Waster Repository, Nye County, Nevada, USA
Currently the US has no long-term storage site for high-level radioactive waste, so it is often just stored on site after use. Looking for a solution to this obvious problem, experts chose Yucca Mountain as a site for a future deep geological repository, as a large part of the formation consists of tuff—a natural barrier to radiation. However, in 2010, funding was pulled under the Obama administration and plans for this site were abandoned, claiming that this was due to political reasons, not technical. Concerns had been raised by many in Nevada, seeing as the formation was already riddled with fractures and that the state ranks fourth in seismic activity in the US.
Images via Speigel.
Schacht Asse II, Lower Saxony, Germany
This abandoned salt mine was used up until the '70s as a repository for low- and medium-level radioactive material, including toxic uranium, rhodium, and plutonium. More than 100,000 barrels are stored over 13 chambers in the deepest corners of the mine. In 2008 it was uncovered that radioactive water was leaking from the mine and started what was the largest environmental panic in postwar-Germany. There is talk of having to remove and relocate barrels to a new location.
Images via BFS.