Nuclear testing is conducted to document function, yield and effects of nuclear weapons during their development. When manufacturing a new nuclear weapon – or upgrading an existing one – it is important to know that everything works as planned, e.g. that it has the assumed yield. The warheads also have to be maximally secure, e.g. insensitive to fire and impossible to use unauthorised. At the same time, they have to be reliable, meaning they must function as intended if triggered in the right way.
During the 20th century, most states developing nuclear weapons have conducted nuclear tests. By testing, states have been able to find out how the weapons work, how they act in different environments, e.g. under water, and how different environments react to nuclear weapons. In addition, nuclear testing has been a means to show off scientific and military strength to the world. Nuclear tests have, in that sense, had an obvious political aspect – a number of states possessing nuclear weapons have announced their nuclear possession through nuclear testing.
More than 2000 nuclear tests have been conducted since the first American test, Trinity, in 1945. More than 500 tests have been done in the atmosphere, under water or in space. The rest have been tested underground. The US is responsible for around 1000 of these tests, the Soviet Union conducted about 700, France 180, China 35 and the UK about 30 tests. India has conducted six tests, Pakistan five and North Korea one nuclear test.
Atmospheric nuclear tests
Atmospheric testing has often been done by detonating nuclear devices from high towers, balloons, barges or islands, or by dropping nuclear bombs from aeroplanes. Occasionally, nuclear devices have been fired from rockets at a very high altitude.
During the 1950′s and 60′s, most nuclear testing was done in the atmosphere. Atmospheric testing is the easiest and cheapest method to conduct and evaluate. However, it involved relatively large amounts of radioactive particles that spread around the globe with the wind, fell and rained to the ground and created a radioactive coating that released radiation.
These environmental consequences got people worrying about the health effects of nuclear testing. Will I fall ill? Will my children and grand children be hurt? Can we farm the land and drink the water close to the test sites? Around the world, a strong opinion grew against nuclear testing in general and atmospheric testing in particular. Indian Prime Minister Nehru brought the world opinion to the UN in 1954, by proposing a world wide nuclear test ban.
Underwater nuclear tests
Underwater testing entails nuclear devices being detonated underwater, usually moored to a ship or a barge. These tests have usually been conducted to evaluate the effects of nuclear weapons against naval vessels, or to evaluate potential sea-based nuclear weapons like submarines or underwater torpedoes. Underwater tests close to the surface can disperse large amounts of radioactive water and steam, contaminating nearby ships or structures.
Underground nuclear tests
Underground testing refers to nuclear tests, which are conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War; other forms of nuclear testing were banned by the Partial Test Ban Treaty in 1963. When the explosion is fully contained, underground nuclear testing emits a negligible amount of fallout.
However, underground nuclear tests can “vent” to the surface, producing considerable amounts of radioactive debris. Underground testing can result in seismic activity depending on the yield of the nuclear device and the composition of the medium it is detonated in, and generally result in the creation of subsidence craters.
Even though the Comprehensive Test Ban Treaty, CTBT, has not yet entered into force, the states signing it have formally undertaken to follow the provisions of the treaty. Hence, no parties to the treaty have conducted any nuclear test since the signing of the treaty. The US, Russia, the UK and France have, to get away from this, conducted other forms of nuclear tests, i.e. Computer simulations, fusion experiments and so called subcritical testing. China, too, is suspected of having conducted at least one subcritical test.
A subcritical test implies testing of fissile materials that can be used for nuclear weapons in amounts that do not reach a critical mass. This means the nuclear reaction can not sustain itself, and the explosion fails. One way to conduct subcritical tests is by using smaller amounts of fissile materials, e.g. a kilo or so of weapon grade uranium or plutonium. The fissile material is compressed by conventional explosive material in a construction at least in some ways resembling the real nuclear weapon, the construction and material of which is to be tested.
The idea with subcritical testing is for nuclear weapon states to be able to continue the development and upgrading of nuclear weapons, while still abiding to the principles of the CTBT.
Last update: December 30, 2015