Project PACER, carried out at Los Alamos National Laboratory (LANL) in the mid-1970s, explored the possibility of a fusion power system that would involve exploding small hydrogen bombs (fusion bombs)—or, as stated in a later proposal, fission bombs—inside an underground cavity. Its proponents claimed that the system is the only fusion power system that could be demonstrated to work using existing technology. It would also require a continuous supply of nuclear explosives and contemporary economics studies demonstrated that these could not be produced at a competitive price compared to conventional energy sources. Development The earliest references to the use of nuclear explosions for power generation date to a meeting called by Edward Teller in 1957. Among the many topics covered, the group considered power generation by exploding 1-megaton bombs in a diameter steam-filled cavity dug in granite. This led to the realization that the fissile material from the fission sections of the bombs, the "primaries", would accumulate in the chamber. Even at this early stage, physicist John Nuckolls became interested in designs of very small bombs, and ones with no fission primary at all. This work would later lead to his development of the inertial fusion energy concept. The initial PACER proposals were studied under the larger Project Plowshares efforts in the United States, which examined the use of nuclear explosions in place of chemical ones for construction. Examples included the possibility of using a large nuclear devices to create an artificial harbour for mooring ships in the north, or as a sort of nuclear fracking to improve natural gas yields. Another proposal would create an alternative to the Panama Canal in a single sequence of detonations, crossing a Central American nation. One of these tests, 1961's Project Gnome, also considered the generation of steam for possible extraction as a power source. LANL proposed PACER as an adjunct to these studies. Early examples considered diameter water-filled caverns created in salt domes at as much as deep. A series of 50-kiloton bombs would be dropped into the cavern and exploded to heat the water and create steam. The steam would then power a secondary cooling loop for power extraction using a steam turbine. Dropping about two bombs a day would cause the system to reach thermal equilibrium, allowing the continual extraction of about 2 GW of electrical power. There was also some consideration given to adding thorium or other material to