The Soviet program started a few years after the U.S. efforts and explored many of the same concepts under their Nuclear Explosions for the National Economy program. The program was more extensive, eventually conducting 239 nuclear explosions. Some of these tests also released radioactivity, including a significant release of plutonium into the groundwater and the polluting of an area near the Volga River. A major part of the program in the 1970s and 80s was the use of very small bombs to produce shock waves as a seismic measuring tool, and as part of these experiments, two bombs were successfully used to seal blown-out oil wells. The program officially ended in 1988.