Nuclear weapons testing
Nuclear weapons tests are experiments carried out to determine the performance, yield, and effects of nuclear weapons. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by different conditions, and how personnel, structures, and equipment are affected when subjected to nuclear explosions. However, nuclear testing has often been used as an indicator of scientific and military strength. Many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status through a nuclear test.
The first nuclear device was detonated as a test by the United States at the Trinity site in New Mexico on July 16, 1945, with a yield approximately equivalent to 20 kilotons of TNT. The first thermonuclear weapon technology test of an engineered device, codenamed Ivy Mike, was tested at the Enewetak Atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States. The largest nuclear weapon ever tested was the Tsar Bomba of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen, an estimated 50–58 megatons.
In 1963, three (UK, US, Soviet Union) of the then four nuclear states and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground nuclear testing. France continued atmospheric testing until 1974, and China continued until 1980. Neither has signed the treaty.[1]
Underground tests conducted by the Soviet Union continued until 1990, the United Kingdom until 1991, the United States until 1992, and both China and France until 1996. In signing the Comprehensive Nuclear-Test-Ban Treaty in 1996, these countries pledged to discontinue all nuclear testing; the treaty has not yet entered into force because of its failure to be ratified by eight countries. Non-signatories India and Pakistan last tested nuclear weapons in 1998. North Korea conducted nuclear tests in 2006, 2009, 2013, January 2016, September 2016 and 2017. The most recent confirmed nuclear test occurred in September 2017 in North Korea.
Separately from these designations, nuclear tests are also often categorized by the purpose of the test itself.
Aside from these technical considerations, tests have been conducted for political and training purposes, and can often serve multiple purposes.
The first atomic weapons test was conducted near Alamogordo, New Mexico, on July 16, 1945, during the Manhattan Project, and given the codename "Trinity". The test was originally to confirm that the implosion-type nuclear weapon design was feasible, and to give an idea of what the actual size and effects of a nuclear explosion would be before they were used in combat against Japan. While the test gave a good approximation of many of the explosion's effects, it did not give an appreciable understanding of nuclear fallout, which was not well understood by the project scientists until well after the atomic bombings of Hiroshima and Nagasaki.
The United States conducted six atomic tests before the Soviet Union developed their first atomic bomb (RDS-1) and tested it on August 29, 1949. Neither country had very many atomic weapons to spare at first, and so testing was relatively infrequent (when the U.S. used two weapons for Operation Crossroads in 1946, they were detonating over 20% of their current arsenal). However, by the 1950s the United States had established a dedicated test site on its own territory (Nevada Test Site) and was also using a site in the Marshall Islands (Pacific Proving Grounds) for extensive atomic and nuclear testing.
The early tests were used primarily to discern the military effects of atomic weapons (Crossroads had involved the effect of atomic weapons on a navy, and how they functioned underwater) and to test new weapon designs. During the 1950s, these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in Kazakhstan. During the later phases of the Cold War, though, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the 20th century.
Atomic and nuclear tests can involve many hazards. Some of these were illustrated in the U.S. Castle Bravo test in 1954. The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react. As a result, the explosion—with a yield of 15 Mt—was over twice what was predicted. Aside from this problem, the weapon also generated a large amount of radioactive nuclear fallout, more than had been anticipated, and a change in the weather pattern caused the fallout to spread in a direction not cleared in advance. The fallout plume spread high levels of radiation for over 100 miles (160 km), contaminating a number of populated islands in nearby atoll formations. Though they were soon evacuated, many of the islands' inhabitants suffered from radiation burns and later from other effects such as increased cancer rate and birth defects, as did the crew of the Japanese fishing boat Daigo Fukuryū Maru. One crewman died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying had made it into the Japanese food supply.
Castle Bravo was the worst U.S. nuclear accident, but many of its component problems—unpredictably large yields, changing weather patterns, unexpected fallout contamination of populations and the food supply—occurred during other atmospheric nuclear weapons tests by other countries as well. Concerns over worldwide fallout rates eventually led to the Partial Test Ban Treaty in 1963, which limited signatories to underground testing. Not all countries stopped atmospheric testing, but because the United States and the Soviet Union were responsible for roughly 86% of all nuclear tests, their compliance cut the overall level substantially. France continued atmospheric testing until 1974, and China until 1980.
A tacit moratorium on testing was in effect from 1958 to 1961 and ended with a series of Soviet tests in late 1961, including the Tsar Bomba, the largest nuclear weapon ever tested. The United States responded in 1962 with Operation Dominic, involving dozens of tests, including the explosion of a missile launched from a submarine.
Almost all new nuclear powers have announced their possession of nuclear weapons with a nuclear test. The only acknowledged nuclear power that claims never to have conducted a test was South Africa (although see Vela incident), which has since dismantled all of its weapons. Israel is widely thought to possess a sizable nuclear arsenal, though it has never tested, unless they were involved in Vela. Experts disagree on whether states can have reliable nuclear arsenals—especially ones using advanced warhead designs, such as hydrogen bombs and miniaturized weapons—without testing, though all agree that it is very unlikely to develop significant nuclear innovations without testing. One other approach is to use supercomputers to conduct "virtual" testing, but codes need to be validated against test data.
There have been many attempts to limit the number and size of nuclear tests; the most far-reaching is the Comprehensive Test Ban Treaty of 1996, which has not, as of 2013, been ratified by eight of the "Annex 2 countries" required for it to take effect, including the United States. Nuclear testing has since become a controversial issue in the United States, with a number of politicians saying that future testing might be necessary to maintain the aging warheads from the Cold War. Because nuclear testing is seen as furthering nuclear arms development, many are opposed to future testing as an acceleration of the arms race.
In total nuclear test megatonnage, from 1945 to 1992, 520 atmospheric nuclear explosions (including eight underwater) were conducted with a total yield of 545 megatons,[21] with a peak occurring in 1961–1962, when 340 megatons were detonated in the atmosphere by the United States and Soviet Union,[22] while the estimated number of underground nuclear tests conducted in the period from 1957 to 1992 was 1,352 explosions with a total yield of 90 Mt.[21]
Yield[edit]
The yields of atomic bombs and thermonuclear are typically measured in different amounts. Thermonuclear bombs can be hundreds or thousands of times stronger than their atomic counterparts. Due to this, thermonuclear bombs' yields are usually expressed in megatons which is about the equivalent of 1,000,000 tons of TNT. In contrast, atomic bombs' yields are typically measured in kilotons, or about 1,000 tons of TNT.
In US context, it was decided during the Manhattan Project that yield measured in tons of TNT equivalent could be imprecise. This comes from the range of experimental values of the energy content of TNT, ranging from 900 to 1,100 calories per gram (3,800 to 4,600 kJ/g). There is also the issue of which ton to use, as short tons, long tons, and metric tonnes all have different values. It was therefore decided that one kiloton would be equivalent to 1.0×1012 calories (4.2×1012 kJ).[23]
United States: 1,054 tests by official count (involving at least 1,149 devices). 219 were atmospheric tests as defined by the CTBT. These tests include 904 at the Nevada Test Site, 106 at the Pacific Proving Grounds and other locations in the Pacific, 3 in the South Atlantic Ocean, and 17 other tests taking place in Amchitka Alaska, Colorado, Mississippi, New Mexico and Nevada outside the NNSS (see Nuclear weapons and the United States for details). 24 tests are classified as British tests held at the NTS. There were 35 Plowshare detonations and 7 Vela Uniform tests; 88 tests were safety experiments and 4 were transportation/storage tests.[24] Motion pictures were made of the explosions, later used to validate computer simulation predictions of explosions.[25] United States' table data.
Soviet Union: 715 tests (involving 969 devices) by official count, plus 13 unnumbered test failures.[26][27] Most were at their Southern Test Area at Semipalatinsk Test Site and the Northern Test Area at Novaya Zemlya. Others include rocket tests and peaceful-use explosions at various sites in Russia, Kazakhstan, Turkmenistan, Uzbekistan and Ukraine. Soviet Union's table data.
United Kingdom: 45 tests, of which 12 were in Australian territory, including three at the Montebello Islands and nine in mainland South Australia at Maralinga and Emu Field,[28] 9 at Christmas Island (Kiritimati) in the Pacific Ocean, plus 24 in the United States at the Nevada Test Site as part of joint test series).[29] 43 safety tests (the Vixen series) are not included in that number, though safety experiments by other countries are. The United Kingdom's summary table.
France: 210 tests by official count (50 atmospheric, 160 underground[30]), four atomic atmospheric tests at C.S.E.M. near Reggane, 13 atomic underground tests at C.E.M.O. near In Ekker in the French Algerian Sahara, and nuclear atmospheric and underground tests at and around Fangataufa and Moruroa Atolls in French Polynesia. Four of the In Ekker tests are counted as peaceful use, as they were reported as part of the CET's APEX (Application pacifique des expérimentations nucléaires, “Peaceful Application of Nuclear Experiments”), and given alternate names. France's summary table.
China: 45 tests (23 atmospheric and 22 underground), at Lop Nur Nuclear Weapons Test Base, in Malan, Xinjiang[31] There are two additional unnumbered failed tests. China's summary table.
India: Six underground explosions (including the first one in 1974), at Pokhran. India's summary table.
Pakistan: Six underground explosions at Ras Koh Hills and the Chagai District.[32] Pakistan's summary table.
North Korea: North Korea is the only country in the world that still tests nuclear weapons, and their tests have caused escalating tensions between them and the United States. Their most recent nuclear test was on September 3, 2017. North Korea's summary table
The nuclear powers have conducted more than 2,000 nuclear test explosions (numbers are approximate, as some test results have been disputed):
There may also have been at least three alleged but unacknowledged nuclear explosions (see list of alleged nuclear tests) including the Vela incident.
From the first nuclear test in 1945 until tests by Pakistan in 1998, there was never a period of more than 22 months with no nuclear testing. June 1998 to October 2006 was the longest period since 1945 with no acknowledged nuclear tests.
A summary table of all the nuclear testing that has happened since 1945 is here: Worldwide nuclear testing counts and summary.
There are many existing anti-nuclear explosion treaties, notably the Partial Nuclear Test Ban Treaty and the Comprehensive Nuclear Test Ban Treaty. These treaties were proposed in response to growing international concerns about environmental damage among other risks. Nuclear testing involving humans also contributed to the formation of these treaties. Examples can be seen in the following articles:
The Partial Nuclear Test Ban treaty makes it illegal to detonate any nuclear explosion anywhere except underground, in order to reduce atmospheric fallout. Most countries have signed and ratified the Partial Nuclear Test Ban, which went into effect in October 1963. Of the nuclear states, France, China, and North Korea have never signed the Partial Nuclear Test Ban Treaty.[33]
The 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions everywhere, including underground. For that purpose, the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization is building an international monitoring system with 337 facilities located all over the globe. 85% of these facilities are already operational.[34] As of May 2012, the CTBT has been signed by 183 States, of which 157 have also ratified. However, for the Treaty to enter into force it needs to be ratified by 44 specific nuclear technology-holder countries. These "Annex 2 States" participated in the negotiations on the CTBT between 1994 and 1996 and possessed nuclear power or research reactors at that time. The ratification of eight Annex 2 states is still missing: China, Egypt, Iran, Israel and the United States have signed but not ratified the Treaty; India, North Korea and Pakistan have not signed it.[35]
The following is a list of the treaties applicable to nuclear testing:
Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. As public awareness and concern mounted over the possible health hazards associated with exposure to the nuclear fallout, various studies were done to assess the extent of the hazard. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that nuclear fallout might have led to approximately 11,000 excess deaths, most caused by thyroid cancer linked to exposure to iodine-131.[37]
The following list is of milestone nuclear explosions. In addition to the atomic bombings of Hiroshima and Nagasaki, the first nuclear test of a given weapon type for a country is included, as well as tests that were otherwise notable (such as the largest test ever). All yields (explosive power) are given in their estimated energy equivalents in kilotons of TNT (see TNT equivalent). Putative tests (like Vela incident) have not been included.