Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant, or WIPP, in New Mexico, US, is a deep geological repository licensed to store transuranic radioactive waste for 10,000 years. The storage rooms at the WIPP are 2,150 feet (660 m) underground in a salt formation of the Delaware Basin. The waste is from the research and production of United States nuclear weapons only. The plant started operation in 1999, and the project is estimated to cost $19 billion in total. It is the world's third such facility, after Germany's Morsleben radioactive waste repository and the Schacht Asse II salt mine.

WIPP is located approximately 26 miles (42 km) east of Carlsbad, in eastern Eddy County, in an area known as the southeastern New Mexico nuclear corridor, which also includes the National Enrichment Facility near Eunice, New Mexico, the Waste Control Specialists low-level waste disposal facility just over the state line near Andrews, Texas, and the International Isotopes, Incorporated facility to be built near Eunice.

Various mishaps at the plant in 2014 brought focus to the problem of what to do with the growing backlog of waste and whether or not WIPP would be a safe repository. The 2014 incidents involved a waste explosion and airborne release of radiological material that exposed 21 plant workers to small doses of radiation that were within safety limits.

In 1970, the United States Atomic Energy Commission, later merged into the Department of Energy (DOE), proposed a site in Lyons, Kansas for the isolation and storage of radioactive waste. Ultimately the Lyons site was deemed unusable due to local and regional opposition, and in particular the discovery of unmapped oil and gas wells located in the area. These wells were believed to potentially compromise the ability of the planned facility to contain nuclear waste. In 1973, as a result of these concerns, and because of positive interest from the southern New Mexico community, the DOE relocated the site of the proposed nuclear waste repository, now called the Waste Isolation Pilot Plant (WIPP), to the Delaware Basin salt beds located near Carlsbad, New Mexico.

The Delaware Basin is a sedimentary basin formed largely during the Permian Period approximately 250 million years ago. It is one of three sub-basins of the Permian Basin in West Texas and Southeastern New Mexico. It contains a 4,900–9,200 ft (1,500–2,800 m) thick column of sedimentary rock that includes some of the most oil- and gas-rich rocks in the United States. An ancient shallow sea repeatedly filled the basin and evaporated while the basin slowly subsided, leaving behind a nearly impermeable 3,300-foot-thick (1,000 m) layer of evaporites, primarily salt, in the Salado and Castile Formations, geologically similar to other basins created by evaporitic inland seas. Over time, the salt beds were covered by an additional 980 ft (300 m) of soil and rock. As drilling in the Salado Formation salt beds began in 1975, scientists discovered that at the edge of the basin there had been geological disturbances that had moved interbed layers into a nearly vertical position. In response, the site was moved toward the more stable center of the basin where the Salado Formation salt beds are the thickest and are perfectly horizontal.

Some observers suggested, early in the investigations, that the geological complexity of the basin was problematic, causing the hollowed-out caverns to be unstable. However, what is considered by some to be instability is considered by others to be a positive aspect of salt as a host rock. As early as 1957, the National Academy of Sciences recommended salt for radioactive waste disposal because at depth it would plastically deform, a motion called "salt creep" in the salt-mining industry. This would gradually fill in and seal any openings created by the mining, and in and around the waste.

Exact placement of the construction site in the Delaware Basin changed multiple times due to safety concerns. Brine deposits located below the salt deposits in the Delaware Basin posed a potential safety problem. The brine was first discovered when a 1975 drilling released a pressurized deposit of the liquid from below the repository level. Constructing the plant near one of these deposits could, under specific circumstances, compromise the facility’s safety. The brine could leak into the repository and either dissolve radioactivity or entrain particulate matter with radioactive waste to the surface. The contaminated brine would then need to be cleaned and properly disposed of. There is no drinking water near the site, so possible water pollution is not a concern. After deep drilling multiple times, a final site was selected. The site is located approximately 25 mi (40 km) east of Carlsbad.

Waste is placed in rooms 2,150 feet (660 m) underground that have been excavated within a 3,000-foot (910 m) thick salt formation (Salado and Castile Formations) where salt tectonics have been stable for more than 250 million years.^{[citation needed]} Because of plasticity effects, salt will flow to any cracks that develop, a major reason why the area was chosen as a host medium for the WIPP project.