Sometime this summer a nuclear-powered Soviet satellite will fall out of orbit and plunge through the atmosphere, potentially repeating the 1978 incident in which radioactive chunks were spewed across northwestern Canada. At that time the secretary of energy, James R. Schlesinger, said that it was "inappropriate to have nuclear reactors orbiting the Earth," and President Jimmy Carter called for banning them altogether. But nothing happened.
The history of nuclear reactors in orbit gives great cause for concern. Their safety record is not good. Between 1961 and 1977 the United States launched 23 such reactors. Four of them (17%) ran into problems, including one that disintegrated on launch, tripling the amount of plutonium-238 in the Earth's environment. While this country does not currently use nuclear power for its satellites, it is planning to orbit as many as 100 nuclear reactors as part of the Strategic Defense Initiative anti-missile program. According to Lt. Gen. James Abrahamson, director of the "Star Wars" project, without nuclear power "that's going to be a long, long light cord that goes down to the surface of the Earth."
For their part, the Soviets have launched 39 nuclear reactors on orbiting satellites since 1965, of which six (15%) have malfunctioned. Cosmos 1900 will be the third to reenter the Earth's atmosphere. (When Cosmos 1402 fell out of orbit in 1983, the Russians were able to eject its reactor from the satellite, and it burned up in the atmosphere with no detectable release of radiation. That option is apparently not available in the case of the satellite that is now about to reenter.)