Accidental Releases

The legacy of nuclear testing and Chernobyl

Editorial revision 2026

Part of the radioactivity in the environment today is due to significant releases of radioactive material occurred in the past. These releases are somehow accidental, because they are not natural but anthropological. Some are deliberate: that is the releases in air of radioactive materials due to the tests of atomic and thermonuclear bombs of the fifties and sixties. Others, involuntary, are due to real accidents : the main accidents are the Chernobyl accident in 1986 and the Fukushima one in 2011.

During this half-century atmosphere of mutual deterrence that was the Cold War, nuclear weapon, a symbol of power, was the tool of this deterrence. The great powers proceeded to many tests of atomic bombs and H bombs. At the beginning of the Cold War, the tests were carried out in air, far from inhabited places in principle. The United States have conducted many tests in the Nevada desert, then on Pacific atolls. The most famous site was that of the Bikini atoll which had been emptied of its inhabitants. France has used for its first tests in 1959-60, the firing site of Reggane in the Sahara, English used the Australian desert, and Chinese the Gobi desert. These atmospheric tests stopped in 1981. Treaties now ban them.

Atmospheric tests released radioactive dust carried by winds that have spread across the globe. They have given rise to a population exposure and contamination of the food chain by some radioisotopes. However, given their radioactive period, most of them have completely disappeared. Remain essentially caesium-137 (period 30 years), strontium-90 (28.6 years) and, to a lesser degree, krypton-85 (a noble gas of period 10.7 years) and tritium (12.3 years period). Traces of americium-241 are still found in small but significant. This radioelement, which was not dispersed during the Chernobyl accident, is an indication of these tests done very far and long ago.

The underground nuclear tests have been cleaner, fission products being in principle confined underground. But there is a risk that by cracking and the action of water, some rise to the surface. France conducted its last underground test in 1995 on the atoll of Mururoa. Nuclear tests were still carried out in 1999 by India and Pakistan, and possibly more recently by North Korea.

A disaster such as the explosion at the Chernobyl nuclear power plant in 1986 released a significant amount of radioactive material (estimated activity released: 12 × 10¹⁸ Bq) near a major city. The nature of the Chernobyl fallout was similar to that of an atmospheric nuclear test.

Ukrainians and Belarusians were by far the most exposed populations. In the first few days after the accident, the most hazardous exposure was due to short-lived iodine isotopes, particularly iodine-131. After iodine-131 had decayed, the main long-term legacy was contamination from deposits of cesium-137.