The Sedan Crater, located at the Nevada National Security Site, is a massive depression resulting from the “Sedan” test, a shallow underground nuclear detonation conducted on July 6, 1962. This event was part of the controversial “Operation Plowshare” program, which explored using nuclear explosives for large-scale engineering projects like creating canals and harbors. After over sixty years, the crater’s existence raises a fundamental question: does it still pose a radioactive threat? The answer lies in understanding the initial explosion, the subsequent decay of radioactive materials, and the careful management of the site.
The Creation of the Sedan Crater
The 1962 Sedan test involved detonating a 104-kiloton thermonuclear device buried at a relatively shallow depth of 635 feet beneath the Nevada desert floor to maximize the earth-moving effect. The force was immense.
The explosion displaced an estimated 12 million tons of soil and rock, creating a massive crater 1,280 feet wide and 320 feet deep. The detonation caused the ground directly above the device to lift into a dome nearly 300 feet high before it vented, releasing a massive cloud of radioactive steam and debris. This immediate venting produced widespread fallout.
The radioactive cloud contaminated a large swath of the United States, exposing more US residents to radiation than any other single nuclear test. This extensive fallout demonstrated the impracticality of using nuclear explosives for peaceful excavation, ultimately leading to the abandonment of the Operation Plowshare program.
Current Radioactivity Levels and Isotope Decay
The Sedan Crater remains radioactive, but current levels are dramatically lower than the hours and days immediately following the 1962 blast. The vast majority of the short-lived radionuclides, which accounted for the initial high radiation readings, have decayed away. The residual activity is primarily due to isotopes with much longer half-lives.
The primary long-term contaminants include Cesium-137, which has a physical half-life of about 30 years. Plutonium isotopes, such as Plutonium-239 (over 24,000 years) and Plutonium-240 (6,500 years), are also present in the soil and pose a risk mainly through ingestion or inhalation. Europium-152 (13.5-year half-life) also contributes to the residual gamma activity in the soil.
The residual contamination is concentrated in the fallout material mixed into the soil on the crater’s lip and floor. A short visit to the crater rim exposes a person to a minimal radiation dose, often comparable to the increase in cosmic radiation received during a cross-country commercial airplane flight. The incremental exposure from a single visit is a tiny fraction of the 620 millirem of radiation the average American is exposed to annually.
Safety Protocols and Public Access
Scientific data showing significantly reduced, yet still present, residual radiation dictates practical safety protocols for site management and public visitors. The Nevada National Security Site (NNSS) operates under strict guidelines to minimize potential exposure. The current exposure risk for a brief, supervised visit is considered negligible, provided visitors adhere to safety instructions.
Public access is strictly controlled and only permitted through guided tours organized by the NNSS. These tours limit the time visitors spend at the site, controlling the total radiation dose they receive. Visitors must remain on designated observation platforms and paved areas to prevent disturbing the soil where residual radionuclides are concentrated.
These measures ensure that the total exposure for a visitor is well within acceptable limits. Site management focuses on limiting exposure time and preventing the inhalation or ingestion of contaminated dust particles. The Sedan Crater is safely accessible today, but access is highly monitored due to the enduring, long-lived radioactive contamination in the soil.