August 29 is the International Day Against Nuclear Tests. The day, declared by the United Nations in 2009, aims to raise awareness of the effects of nuclear weapons testing and to achieve a world without nuclear weapons.
On July 16, 1945, during World War II, the United States detonated the world’s first nuclear weapon, codenamed Trinity, over the New Mexico desert.
Less than a month later, the US dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki, killing more than 100,000 people instantly.
Thousands more died from their injuries, radiation sickness and cancer in the following years, bringing the total closer to 200,000, according to the US Department of Energy’s history of the Manhattan Project.
Nuclear warheads per country
Nine countries possessed an estimated 12,700 warheads as of early 2022, according to the Federation of American Scientists. Approximately 90 percent are owned by Russia (5,977 warheads) and the United States (5,428 warheads).
At their peak in 1986, the two rivals had nearly 65,000 nuclear warheads between them, making the nuclear arms race one of the most threatening events of the Cold War.
While Russia and the US have dismantled thousands of warheads, several countries are believed to be increasing their stockpiles, notably China.
The only country that has voluntarily given up nuclear weapons is South Africa. In 1989, the government suspended its nuclear weapons program and in 1990 began dismantling its six nuclear weapons. In 1991, South Africa joined the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) as a non-nuclear state.
Which countries have carried out nuclear tests?
According to the Arms Control Association, at least eight countries have conducted a total of 2,056 nuclear tests since 1945.
The US conducted half of all nuclear tests, with 1,030 tests between 1945 and 1992. In 1954, the US detonated its largest nuclear weapon, a 15-megaton bomb, on the surface of Bikini Atoll in the Marshall Islands, a test code-named Castle Bravo. The power of the nuclear test was miscalculated by scientists, and this led to radiation pollution that affected the inhabitants of the atolls. Nuclear debris from the explosion is estimated to have spread over 18,130 square kilometers (7,000 sq mi).
The Soviet Union conducted the second largest number of nuclear tests with 715 tests between 1949 and 1990. The USSR’s first nuclear test was on August 29, 1949. The test, codenamed RDS-1, was conducted at the Semipalatinsk test site in Kazakhstan. According to the CTBTO, the Soviet Union conducted 456 tests at the Semipalatinsk test site with devastating consequences for the local population such as genetic defects and high rates of cancer.
Kazakhstan closed the Semipalatinsk test site on August 29, 1991. Following this move, the United Nations established August 29 as the International Day Against Nuclear Tests in 2009.
France has conducted 210 nuclear tests, while the United Kingdom and China have conducted 45 each.
India has conducted three nuclear tests while Pakistan has conducted two.
North Korea is the latest nation to conduct a nuclear test. In 2017, its sixth and most powerful bomb was detonated at the Punggye-ri nuclear test site. The underground explosion caused an earthquake with a magnitude of 6.3 on the Richter scale.
The largest nuclear detonations
The largest nuclear explosion occurred in 1961, when the Soviet Union detonated the Tsar Bomba on Novaya Zemlya, north of the Arctic Circle. The power of the explosion was 50 megatons, 3300 times more powerful than the nuclear bomb dropped on Hiroshima.
Other major nuclear explosions by various nations include China’s largest detonation at Lop Nur in 1976, a test with a yield of four megatons.
The United Kingdom conducted a series of nuclear tests in the South Pacific between November 1957 and September 1958 as part of Operation Grapple. Grapple Y was the largest of the operation’s nuclear tests at three megatons.
A 1999 study by the British Nuclear Veterans Association found that the impact of the tests on 2,500 veterans who attended showed that more than 200 had skeletal abnormalities and 30 percent of the men died, mostly in their fifties. .
In 1968, France conducted a series of nuclear tests, codenamed Canopus, on Phangataufa Atoll in the South Pacific. The test had a yield of 2.6 megatons and was 200 times more powerful than the Hiroshima bomb.
Nuclear test sites
Nuclear weapons have been tested all over the world.
On February 13, 1960, France conducted its first nuclear test, codenamed Gerboise Bleue, over the Sahara desert in Algeria, which it occupied at the time.
Other nuclear test sites include a number in the United States in the states of Nevada, New Mexico, Colorado, and Mississippi.
Tests have been conducted in Australia, China, India, Kazakhstan, North Korea, Russia and Pakistan, as well as in French Polynesia, Kiritimati, the Marshall Islands, Prince Edward Island in the Indian Ocean and in the high seas of the eastern Pacific and southern Atlantic Ocean.
In 1979, the American Vela satellite detected an atmospheric nuclear explosion over Prince Edward Island in the Indian Ocean. Many believe it was an undeclared joint nuclear test carried out by South Africa and Israel.
What does a nuclear test involve?
Nuclear explosions are detonated either in the atmosphere or underground.
About a quarter of all nuclear tests have been detonated in the atmosphere, spreading radioactive materials into the air. To minimize the release of radioactive material, most nuclear tests are conducted underground.
Before conducting a nuclear test, a suitable test site must be found and prepared. A hole is drilled in the ground into which the nuclear device is placed.
The hole is covered with gravel, sand and other materials to prevent radioactive material from escaping. Radiation monitors are activated and aircraft circle the test site to track the device’s capabilities by reviewing weather and fallout patterns.
When the device is detonated, energy is released almost instantaneously, creating high temperatures and pressures that vaporize the nuclear device and the surrounding underground rock zone.
A cavity forms where the detonation occurred, and as the hot gases cool, pools of molten rock collect at the bottom of the cavity. After some time, the weight of the overburden causes the roof of the cavity to collapse and a chimney of gravel extends to the surface, forming a subsidence crater—a bowl-shaped depression up to 600 m (1,969 ft) in diameter and up to 60 m (197 ft) deep. .
After the test, the site remains secured – samples and data are retrieved later.
Exposure to different levels of radiation
Nuclear tests have immediate and long-term effects caused by radiation and radioactive waste. Increased rates of cancer have been associated with nuclear testing, with studies showing that thyroid cancer is linked to radionuclides.
After a nuclear test, large areas of land remain radioactive decades after the test.
The health effects of different levels of radiation range from nausea and vomiting to death within days.
Radiation exposure is measured in human x-ray equivalent (rem) – a unit of measurement of radiation applied to people as a result of exposure to one or more types of ionizing radiation.
The infographic below shows the effects of radiation on the human body.