Beneath this innocuous plaque 25 miles from downtown Carlsbad lies the site of a second nuclear explosion in New Mexico. Unlike the Trinity Site, this explosion was underground and had a peaceful purpose. My own grandfather was employed for it's construction.
Initially delayed by a nuclear testing moratorium with the Soviet Union, Project Gnome was intended to:
Study the possibility of converting the heat produced by a nuclear explosion into steam for the production of electric power,
Explore the feasibility of recovering radioisotopes for scientific and industrial applications,
Use the high flux of neutrons produced by the detonation for a variety of measurements that would contribute to reactor development, and
Further develop the ability of the United States to detect underground and high-altitude nuclear detonations.
During 1957 underground nuclear tests, scientists learned that an underground detonation created large quantities of heat and radioisotopes that quickly become trapped in the molten rock and become unusable as the rock resolidifed. For this reason, it was decided that Gnome would be detonated in salt bedrock southeast of Carlsbad. The Geology of the site is similar to the present-day WIPP site.
The plan was to pipe water through the molten salt and use the generated steam to produce electricity. The hardened salt could then be dissolved in water to extract the radioisotopes. Gnome was considered important to show that nuclear weapons might be used in peaceful applications.
The nuclear device was placed 1,184 ft underground at the end of a tunnel that was supposed to be self-sealing upon detonation. It was detonated on December 10, 1961. The detonation was supposed to seal itself, the plan did not work. A few minutes after the explosion, smoke and steam began to rise from the shaft. Some radiation was released. The cavity created was almost 1,000,000 cubic feet (170 ft wide and 90 ft high) with a floor of melted rock and salt.
A new shaft was drilled near the first and on May 17, 1962, crews entered the Gnome Cavity. Even though almost six months had passed since the detonation, the temperature inside the cavity was still around 140 °F. Inside, they found stalactites made of melted salt. The intense radiation of the detonation colored the salt multiple shades of blue, green, and violet. The crews entered the cavern and crossed the rubble pile. The explosion had melted 2400 tons of salt and had caused the collapse of the sides and top of the chamber. This adding 28,000 tons of rubble that mixed with the molten salt and rapidly reduced its temperature. This was the reason for the failure of the test to be viable to produce electricity since they had initially recorded temperatures of only 200 °F without high pressure steam and only small pockets of molten salt at up to 1,450 °F.