Since the development of nuclear bombs in the 1940s, suggestions have been made for possible civilian peaceful uses of these powerful explosives. The United States explored some of these possibilities in Operation Plowshare and the Soviet Union worked on them in their Nuclear Explosives for the National Economy program. The primary use was for large scale earth moving but there were other uses such as seismic exploration and sealing major leaks in gas fields that were considered. Despite the hostility between these two nations during the Cold War, there were several bilateral conferences where scientists from the two nations compare notes on their experiments. After over one hundred explosions were triggered during the tests, in the end, both of these projects were cancelled due to technical problems, environmental pollutions and public opposition. Since the Soviet ended its program in 1989, there have been no other serious explorations of peaceful use of nuclear explosions.
Another plan for peaceful use of nuclear explosions that never got beyond the study and planning stage called for the use of nuclear explosions to generate electricity. The idea had been around since 1957 when it was suggested that megaton fusion bombs be exploded in a cavity dug out of solid granite to heat steam. As part of Operation Plowshare, Los Alamos National Laboratories researched the concept under the name Project PACER during the 1970s. They considered the use of thermonuclear fusion bombs but later decided that atomic fission bombs would be a better choice.
The basic idea was create an underground chamber where nuclear devices could be exploded to heat steam for power generation. An early design called for a one thousand foot diameter dug five thousand feet underground in a salt dome. It would be filled with water. Fifty kiloton bombs would be dropped in at about the rate of two a day. The resulting steam would be run through a heat exchanger and the secondary steam would power a generator. Estimates were made that two gigawatt of energy could be generated in this way
A later design called for kiloton nuclear bombs to be detonated every forty five minutes. The heat of their explosion would be captured by molten salts running down the side of the chamber. The molten salts would enter a heat exchanger where the heat would be used to generate steam. The steam could then drive a turbine to create electricity.
After the cancellation of Operation Plowshare, additional studies and designs have been explored. One of these later designs was based on a steel cylinder one hundred feet in diameter and three hundred feet tall with walls that were four feet thick. The cylinder would be embedded in concrete in a hole in the ground. The cylinder would be half full of molten salts which would be continuously pumped to the top and allowed to flow down. In this rain of molten salt, a one kiloton fission bomb would be detonated every forty five minutes. A heat exchanger would generate steam from the molten salt to drive a turbine and generate electricity.
One of the problems with these bomb generator is that they would require a steady supply of small nuclear bombs which would make the economic feasibility of such a system less attractive. The cost of fueling a PACER style system was estimated in one study to be about ten times the cost of fueling a conventional light water reactor.
